John Chew

Professor John Chew


Professor of Mechanical Engineering
+44 (0)1483 686284

Academic and research departments

Department of Mechanical Engineering Sciences.

Biography

Research interests

  • Fluid Dynamics, Heat Transfer and Aero-elasticity
  • Methods for and Application of Computational and Theoretical Fluid Dynamics and Heat Transfer.
  • Turbo-machinery internal flow systems and seals

Departmental duties

Professor of Mechanical Engineering

Editor of the Journal of Mechanical Engineering Science (Proc. IMechE Part C).

Technical Programme Chair for ASME Turbo Expo 2016.

Member of the Aerodynamics National Technical Committee.

Member of the Engineering and Physical Sciences Research Council College Peer Review College.

Current Research Programmes

  • Large Eddy Simulation (LES) methods for flow and heat transfer prediction in rotating disc cavities
  • Unsteady Simulation of Rim Sealing in Turbine Cavities
  • Pre-Swirl Systems for Cooling Air Delivery
  • Fluid-Solid Aero-Thermo-Mechanical Coupling for Industrial Flows
  • Brush Seal Modelling
  • Modelling Techniques for Buoyancy-affected Flow in Turbomachinery Disc Cavities
  • Thermal Contact Resistance

My publications

Publications

Chen LH, Wood PE, Jones TV, Chew JW (2000) Detailed experimental studies of flow in large scale brush seal model and a comparison with CFD predictions, JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER-TRANSACTIONS OF THE ASME 122 (4) pp. 672-679 ASME-AMER SOC MECHANICAL ENG
Chew J, Green T, Turner A (1994) Rim sealing of rotor-stator wheelspaces in the presence of external flow, Proceedings of the ASME Turbo Expo 1
Copyright © 1994 by ASME.Sealing of the cavity formed between a rotating disc and a stator with an asymmetric external flow is considered. In these circumstances circumferential pressure variations in the external flow and the pumping action of the disc may draw fluid into the cavity. Gas concentration measurements, showing this effect, have been obtained from a model experiment with a simple axial clearance seal. In the experiment, guide vanes, fitted upstream of the rim seal, generate an asymmetric external flow. The measurements are shown to be in reasonable agreement with three-dimensional computational fluid dynamics (CFD) calculations and are also compared with more elementary models. The CFD results give further insight into the effects of ingestion within the cavity.
Dadkhah S, Turner A, Chew J (1991) Performance of radial clearance rim seals in upstream and downstream rotor-stator wheelspaces, American Society of Mechanical Engineers (Paper)
A new experimental facility for the investigation of rim sealing is described and measurements are presented for two representative radial clearance seals with a nominally axisymmetric external flow. One radial seal has an upward rotor lip and is upstream of the rotor while the other has an upward stator lip and is downstream of the rotor. Measurements include surface pressures, tangential velocities in the core region of the disc cavity flow, and traverses of gas concentration in the cavity showing the distribution of mainstream ingestion. Tests were conducted at rotational Reynolds numbers up to 3 × 106 with nominal seal clearance to radius ratios in the range 0.002 to 0.01. For the radial seals a differential pressure criterion is found to overestimate the minimum sealing flow. Tangential velocity measurements in the wheelspace are in excellent agreement with other workers measurements and with theoretical predictions.
Chew J, Autef V, Hills N, Brunton I (2007) Turbine Stator-well flow modelling,
In axial gas turbines, hot air from the main annulus path
tends to be ingested into the turbine disc cavities. This leads to
overheating which will reduce the disc?s life time or lead to
serious damage. Often, to overcome this problem, some air is
extracted from the compressor to cool the rotor discs. This
also helps seal the rim seals and to protect the disc from the
hot annulus gas. However, this will deteriorate the overall
efficiency. A detailed knowledge of the flow interaction between
the main gas path and the disc cavities is necessary in
order to optimise thermal effectiveness against overall efficiency
due to losses of the cooling air from the main gas path.
The aim of this study is to provide better understanding of
the flow in a turbine stator-well, and evaluate the use of different
CFD methods for this complex, 3-dimensional unsteady
flow. This study presents CFD results for a 2-stage turbine.
The stator-well cavity for the second row of stationary vanes
is included in the calculation and results for both turbine performance
and stator-well sealing efficiency are presented.
Kassimatis PG, Bergeles GC, Jones TV, Chew JW (2000) Numerical investigation of the aerodynamics of the near-slot film cooling, INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS 32 (1) pp. 97-117 JOHN WILEY & SONS LTD
O'Mahoney T, Hills N, Chew J (2012) Sensitivity of les results from turbine rim seals to changes in grid resolution and sector size, Progress in Aerospace Sciences 52 pp. 48-55
Large-Eddy Simulations (LES) were carried out for a turbine rim seal and the sensitivity of the results to changes in grid resolution and the size of the computational domain are investigated. Ingestion of hot annulus gas into the rotor-stator cavity is compared between LES results and against experiments and Unsteady Reynolds-Averaged Navier-Stokes (URANS) calculations. The LES calculations show greater ingestion than the URANS calculation and show better agreement with experiments. Increased grid resolution shows a small improvement in ingestion predictions whereas increasing the sector model size has little effect on the results. The contrast between the different CFD models is most stark in the inner cavity, where the URANS shows almost no ingestion. Particular attention is also paid to the presence of low frequency oscillations in the disc cavity. URANS calculations show such low frequency oscillations at different frequencies than the LES. The oscillations also take a very long time to develop in the LES. The results show that the difficult problem of estimating ingestion through rim seals could be overcome by using LES but that the computational requirements were still restrictive. © 2011 Elsevier Ltd. All rights reserved.
Chew JW, Lapworth BL, Millener PJ (1995) Mathematical modeling of brush seals, International Journal of Heat and Fluid Flow 16 (6) pp. 493-500
A computational fluid dynamics (CFD)-based model of brush seals has been developed and tested against other workers' experimental data. In the model, the brush is treated as an axisymmetric, anisotropic porous region with nonlinear resistance coefficients. The resistance coefficients are chosen through calibration against measurements. The CFD model gives predictions of flow rate, pressure distribution, velocity field, and bending forces on the bristles. The bristle forces are used in a separate calculation to estimate bristle bending and reaction forces on the shaft and backing plate. Bending in both the axial direction and the orthogonal plane are considered. © 1995.
Chew J, DADKHAH S, TURNER A (1992) RIM SEALING OF ROTOR-STATOR WHEELSPACES IN THE ABSENCE OF EXTERNAL FLOW, JOURNAL OF TURBOMACHINERY-TRANSACTIONS OF THE ASME 114 (2) pp. 433-438 ASME-AMER SOC MECHANICAL ENG
Ganine V, Javiya U, Hills N, Chew J (2012) Coupled fluid-structure transient thermal analysis of a gas turbine internal air system with multiple cavities, Journal of Engineering for Gas Turbines and Power 134 (10)
This paper presents the transient aerothermal analysis of a gas turbine internal air system through an engine flight cycle featuring multiple fluid cavities that surround a HP turbine disk and the adjacent structures. Strongly coupled fluid-structure thermal interaction problems require significant computational effort to resolve nonlinearities on the interface for each time step. Simulation times may grow impractical if multiple fluid domains are included in the analysis. A new strategy is employed to decrease the cost of coupled aerothermal analysis. Significantly lower fluid domain solver invocation counts are demonstrated as opposed to the traditional coupling approach formulated on the estimates of heat transfer coefficient. Numerical results are presented using 2D finite element conduction model combined with 2D flow calculation in five separate cavities interconnected through the inlet and outlet boundaries. The coupled solutions are discussed and validated against a nominal stand-alone model. Relative performance of both coupling techniques is evaluated. © 2012 American Society of Mechanical Engineers.
Beard PF, Chew J, Gao F, Chana KS (2016) UNSTEADY FLOW PHENOMENA IN TURBINE RIM SEALS, Proceedings of ASME Turbo Expo 2016
While turbine rim sealing flows are an important aspect of turbomachinery design, affecting turbine aerodynamic performance and turbine disc temperatures, the present understanding and predictive capability for such flows is limited. The aim of the present study is to clarify the flow physics involved in rim sealing flows and to provide high quality experimental data for use in evaluation of CFD models. The seal considered is similar to a chute seal previously investigated by other workers, and the study focuses on the inherent unsteadiness of rim seal flows, rather than unsteadiness imposed by the rotating blades. Unsteady pressure measurements from radially and circumferentially distributed transducers are presented for flow in a rotor-stator disc cavity and the rim seal without imposed external flow. The test matrix covered ranges in rotational Reynolds number, Re?, and non-dimensional flow rate, , of 2.2 ?3.0x106 and 0 ? 3.5x103 respectively. Distinct frequencies are identified in the cavity flow and detailed analysis of the pressure data associates these with large scale flow structures rotating about the axis. This confirms the occurrence of such structures as predicted in previously published CFD studies and provides new data for detailed assessment of CFD models.
Chew JW, Birch NT (1987) COMPARISON BETWEEN NUMERICAL SOLUTIONS AND MEASUREMENTS FOR A HIGH-SPEED TURBINE BLADE., I Mech E Conference Publications (Institution of Mechanical Engineers) pp. 73-80
Detailed comparisons between finite difference solutions of the Reynolds averaged Navier-Stokes equations and other workers' measurements for a high speed low-pressure turbine blade are reported. Two turbulence models are considered: an algebraic model and a one equation model which includes a treatment of laminar-turbulent transition. The comparison with experimental data includes surface pressure distribution, transition and separation locations, velocity traverses, boundary layer parameters and total pressure loss. Accuracy of the numerical solution and adequacy of the turbulence models are investigated. The overall accuracy of the predictions is most severely limited by transition modelling.
Guardino C, Chew JW, Hills NJ (2002) Calculation of surface roughness effects on air-riding seals, American Society of Mechanical Engineers, International Gas Turbine Institute, Turbo Expo (Publication) IGTI 3 B pp. 795-803
The effects of surface roughness on air-riding seals are investigated here using the Rayleigh-pad as an example. Both incompressible and compressible flows are considered using both CFD analysis and analytical/numerical solutions of the Reynolds equation for various 2D or 3D roughness patterns on the stationary wall. A 'unit-based' approach for incompressible flows has also been employed and is shown to be computationally much less expensive than the full-geometry solution. Results are presented showing the effect of surface roughness on the net lift force. The effects of varying the Reynolds number are demonstrated, as well as comparative results for static stiffness.
Javiya U, Chew JW, Hills NJ, Zhou L, Wilson M, Lock GD (2011) CFD analysis of flow and heat transfer in a direct transfer preswirl system, Journal of Turbomachinery 134 (3)
Javiya U, Chew J, Hills N, Scanlon T (2011) A comparative study of cascade vanes and drilled nozzle designs for pre-swirl, Proceedings of the ASME Turbo Expo 5 (PARTS A AND B) pp. 913-920
Design of pre-swirl systems is important for the secondary air cooling system of gas turbine engines. In this paper, three pre-swirl nozzles, a cascade vane and two drilled nozzles are analysed and their performances are compared. The two drilled nozzles considered are a straight drilled nozzle and an aerodynamically designed nozzle. CFD analyses are presented for stand-alone and pre-swirl system 3D sector models at engine operating conditions near to engine maximum power condition rotational Reynolds number (ReÆ?) up to 4.6 ! 107. Nozzle performance is characterised by the nozzle discharge coefficient (CD), nozzle velocity coefficient (?·) and cooling air delivery temperature. Two commonly used eddy viscosity models are employed for the study, the standard º-µ and Spalart-Allmaras models with wall functions. Both models give very similar results for CD and · and are in reasonable agreement with available experimental data. Effects of nozzle or vane number and sealing flow have been analysed. The cascade vanes perform slightly better than the aerodynamically designed drilled nozzles but the final design choice will depend on other component and manufacturing costs. An elementary model is presented to separate temperature losses due to the nozzle, stator drag and sealing flow. Copyright © 2011 by Rolls-Royce plc.
Noor Mohamed S, Chew J, Hills N (2016) Flow and windage due to bolts on a rotating disc, Journal of Mechanical Engineering Science (Part C, Proc. IMechE) Sage
The cooling air in a rotating machine is subject to windage as it passes over the rotor surface, particularly for cases where non-axisymmetric features such as boltheads are encountered. The ability to accurately predict windage can help reduce the quantity of cooling air required, resulting in increased efficiency. Previous work has shown that steady CFD solutions can give reasonable predictions for the effects of bolts on disc moment for a rotor-stator cavity with throughflow but flow velocities and disc temperature are not well predicted. Large fluctuations in velocities have been observed experimentally in some cases. Time-dependent CFD simulations reported here bring to light the unsteady nature of the flow. Unsteady Reynolds averaged Navier-Stokes (URANS) calculations for 120 degree and 360 degree models of the rotor-stator cavity with 9 and 18 bolts were performed in order to better understand the flow physics. Although the rotor-stator cavity with bolts is geometrically steady in the rotating frame of reference, it was found that the bolts generate unsteadiness which creates time-dependent rotating flow features within the cavity. At low throughflow conditions, the unsteady flow significantly increases the average disc temperature.
Javiya U, Chew J, Hills N, Zhou L, Wilson M, Lock G (2010) CFD ANALYSIS OF FLOW AND HEAT TRANSFER IN A DIRECT TRANSFER PRE-SWIRL SYSTEM, PROCEEDINGS OF THE ASME TURBO EXPO 2010, VOL 4, PTS A AND B pp. 1167-1178 AMER SOC MECHANICAL ENGINEERS
Chew JW, Vaughan CM (1988) Numerical predictions for the flow induced by an enclosed rotating disc, Proceedings of the ASME Turbo Expo 1
Copyright © 1988 by ASME.Finite difference solutions are presented for turbulent flow in the cavity formed between a rotating and a stationary disc, with and without a net radial outflow of fluid. The mean flow is assumed steady and axisymmetric and a mixing length model of turbulence is used. Grid dependency of the solutions is shown to be acceptably small and results are compared with other workers' experimental data. Theoretical and measured disc moment coefficients are in good agreement, while theoretical and measured velocities are in reasonable agreement. It is concluded that the mixing-length model is sufficiently accurate for many engineering calculations of boundary layer dominated flows in rotating disc systems.
Kumar BGV, Chew JW, Hills NJ (2013) Rotating Flow and Heat Transfer in Cylindrical Cavities With Radial Inflow, JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER-TRANSACTIONS OF THE ASME 135 (3) ARTN 032502 ASME
Virr GP, Chew JW, Coupland J (1993) Application of computational fluid dynamics to turbine disc cavities, American Society of Mechanical Engineers (Paper)
A CFD code for the prediction of flow and heat transfer in rotating turbine disc cavities is described and its capabilities demonstrated through comparison with available experimental data. Application of the method to configurations typically found in aeroengine gas turbine is illustrated and discussed. The code employs boundary-fitted coordinates and uses the º-µ turbulence model with alternative near-wall treatments. The wall function approach and a one-equation near-wall model are compared and it is shown that there are particular limitations in the use of wall functions at low rotational Reynolds number.
Noor Mohamed S, Chew J, Hills N J (2016) EFFECT OF BOLTS ON FLOW AND HEAT TRANSFER IN A ROTOR-STATOR DISC, Proceedings of ASME Turbo Expo 2016
Previous studies have indicated some differences between steady CFD predictions of flow in a rotor-stator disc cavity with rotating bolts compared to measurements. Recently time-dependent CFD simulations have revealed the unsteadiness present in the flow and have given improved agreement with measurements. In this paper unsteady Reynolds averaged Navier-Stokes (URANS) 3600 model CFD calculations of a rotor-stator cavity with rotor bolts were performed in order to better understand the flow and heat transfer within a disc cavity previously studied experimentally by other workers. It is shown that the rotating bolts generate unsteadiness due to wake shedding which creates time-dependent flow patterns within the cavity. At low throughflow conditions, the unsteady flow significantly increases the average disc temperature. A systematic parametric study is presented giving insight into the influence of number of bolts, mass flow rate, cavity gap ratio and the bolts-to-shroud gap ratio on the time depended flow within the cavity.
Chew J, Green T, Turner A (1994) Rim sealing of rotor-stator wheelspaces in the presence of external flow, American Society of Mechanical Engineers (Paper) pp. 1-12
Sealing of the cavity formed between a rotating disc and a stator with an asymmetric external flow is considered. In these circumstances circumferential pressure variations in the external flow and the pumping action of the disc may draw fluid into the cavity. Gas concentration measurements, showing this effect, have been obtained from a model experiment with a simple axial clearance seal. In the experiment, guide vanes, fitted upstream of the rim seal, generate an asymmetric external flow. The measurements are shown to be in reasonable agreement with three-dimensional computational fluid dynamics (CFD) calculations and are also compared with more elementary models. The CFD results give further insight into the effects of ingestion within the cavity.
Pitz Diogo B., Chew John W., Marxen Olaf, Hills Nicholas J. (2017) Direct Numerical Simulation of Rotating Cavity Flows Using a Spectral Element-Fourier Method, Journal of Engineering for Gas Turbines and Power: Transactions of the ASME 139 (7) 072602 ASME
in a rotor/stator cavity without heat transfer and buoyant flow in a rotor/rotor cavity. The numerical tool used employs a spectral element discretisation in two dimensions and a Fourier expansion in the remaining direction, which is periodic and corresponds to the azimuthal coordinate in cylindrical coordinates. The spectral element approximation uses a Galerkin method to discretise the governing equations, but employs high-order polynomials within each element to obtain spectral accuracy. A second-order, semi-implicit, stiffly stable algorithm is used for the time discretisation. Numerical results obtained for the rotor/ stator cavity compare favourably with experimental results for Reynolds numbers up to Re1 = 106 in terms of velocities and Reynolds stresses. The buoyancy-driven flow is simulated using the Boussinesq approximation. Predictions are compared with previous computational and experimental results. Analysis of the present results shows close correspondence to natural convection in a gravitational field and consistency with experimentally observed flow structures in a water-filled rotating annulus. Predicted mean heat transfer levels are higher than the available measurements for an air-filled rotating annulus, but in agreement with correlations for natural convection under gravity.
Ganine V, Javiya U, Hills N, Chew J (2012) Coupled fluid-structure transient thermal analysis of a gas turbine internal air system with multiple cavities, Proceedings of the ASME Turbo Expo 4 (PARTS A AND B) pp. 2167-2177
This paper presents the transient aero-thermal analysis of a gas turbine internal air system through an engine flight cycle featuring multiple fluid cavities that surround a HP turbine disk and the adjacent structures. Strongly coupled fluid-structure thermal interaction problems require significant computational effort to resolve nonlinearities on the interface for each time step. Simulation times may grow impractical if multiple fluid domains are included in the analysis. A new strategy is employed to decrease the cost of coupled aero-thermal analysis. Significantly lower fluid domain solver invocation counts are demonstrated as opposed to the traditional coupling approach formulated on the estimates of heat transfer coefficient. Numerical results are presented using 2D FE conduction model combined with 2D flow calculation in five separate cavities interconnected through the inlet and outlet boundaries. The coupled solutions are discussed and validated against a nominal stand-alone model. Relative performance of both coupling techniques is evaluated. Copyright © 2012 by ASME.
Chew JW, Guardino C (2004) Simulation of flow and heat transfer in the tip region of a brush seal, INTERNATIONAL JOURNAL OF HEAT AND FLUID FLOW 25 (4) pp. 649-658 ELSEVIER SCIENCE INC
Koli B, Chew JW, Hills NJ, Scanlon T (2014) CFD INVESTIGATION OF A FLUIDIC DEVICE FOR MODULATION OF AERO-ENGINE COOLING AIR, PROCEEDINGS OF THE ASME TURBO EXPO: TURBINE TECHNICAL CONFERENCE AND EXPOSITION, 2014, VOL 5C AMER SOC MECHANICAL ENGINEERS
Guardino C, Chew J, Hills N (2004) Calculation of surface roughness effects on air-riding seals, JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER-TRANSACTIONS OF THE ASME 126 (1) pp. 75-82 ASME-AMER SOC MECHANICAL ENG
Smout PD, Chew JW, Childs PRN (2002) ICAS-GT: A European collaborative research programme on internal cooling air systems for gas turbines, American Society of Mechanical Engineers, International Gas Turbine Institute, Turbo Expo (Publication) IGTI 3 B pp. 907-914
The Internal Cooling Air Systems for Gas Turbines (ICAS-GT) research programme, sponsored by the European Commission, ran from January 1998 to December 2000, and was undertaken by a consortium of ten gas turbine manufacturing companies and four universities. Research was concentrated in five discrete but related areas of the air system including turbine rim seals, rotating cavity flow and heat transfer, and turbine pre-swirl system effectiveness. In each case, experiments were conducted to extend the database of pressure, temperature, flow and heat transfer measurements to engine representative non-dimensional conditions. The data was used to develop correlations, and to validate CFD and FE calculation methods, for internal fluid flow and heat transfer. This paper summarises the outcome of the project by presenting a sample of experimental results from each technical work package. Examples of the associated CFD calculations are included to illustrate the progress made in developing validated tools for predicting rotating cavity flow and heat transfer over an engine representative range of flow conditions.
Hutcheson PS, Chew JW, Thorpe RB, Young C, Regan NJ (2009) MODELLING OF LIQUID LEAKAGE SPRAYS IN CROSSFLOW, PROCEEDINGS OF THE ASME TURBO EXPO 2009, VOL 3, PTS A AND B pp. 1183-1195 AMER SOC MECHANICAL ENGINEERS
Gopal V, Whiting MJ, Chew JW, Mills S (2012) FINITE ELEMENT ANALYSIS AS A TOOL FOR CALCULATING THE THERMAL CONTACT CONDUCTANCE FOR A MACHINED SURFACE, PROCEEDINGS OF THE ASME SUMMER HEAT TRANSFER CONFERENCE, 2012, VOL 1 pp. 643-650 AMER SOC MECHANICAL ENGINEERS
Chew JW (2009) Developments in turbomachinery internal air systems, PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART C-JOURNAL OF MECHANICAL ENGINEERING SCIENCE 223 (1) pp. 189-193 PROFESSIONAL ENGINEERING PUBLISHING LTD
Verdicchio JA, Chew JW, Hills NJ (2001) Coupled fluid/solid heat transfer computation for turbine discs, Proceedings of the ASME Turbo Expo 3
This paper considers the coupling of a finite element thermal conduction solver with a steady, finite volume fluid flow solver. Two methods were considered for passing boundary conditions between the two codes - transfer of metal temperatures and either convective heat fluxes or heat transfer coefficients and air temperatures. These methods have been tested on two simple rotating cavity test cases and also on a more complex real engine example. Convergence rates of the two coupling methods were compared. Passing heat transfer coefficients and air temperatures was found to give the quickest convergence. The coupled method gave agreement with the analytic solution and a conjugate solution of the simple free disc problem. The predicted heat transfer results for the real engine example showed some encouraging agreement, although some modelling issues are identified. Copyright © 2001 by ASME.
CHEW JW (1985) COMPUTATION OF CONVECTIVE LAMINAR-FLOW IN ROTATING CAVITIES, JOURNAL OF FLUID MECHANICS 153 (APR) pp. 339-360 CAMBRIDGE UNIV PRESS
Turner MT, Chew JW, Long CA (1998) Experimental investigation and mathematical modeling of clearance brush seals, JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER-TRANSACTIONS OF THE ASME 120 (3) pp. 573-579 ASME-AMER SOC MECHANICAL ENG
Chen LH, Wood PE, Jones TV, Chew JW (1999) Detailed experimental studies of flow in large scale brush seal model and a comparison with CFD predictions, Proceedings of the ASME Turbo Expo 3
Copyright © 1999 by ASME All Rights Reserved.A five times scale model of an engine brush seal has been manufactured. The bristle stiffness and pressure were chosen to satisfy close similarity of the relevant non-dimensional parameters, and the choice of parameters is described. The comparison of flow characteristics for the model seal and an engine seal confirmed the non-dimensional similarity. Detailed pressure measurements were performed within the bristle pack by employing hollow bristles. This novel measurement allowed insight to be obtained into the operation of both clearance and interference seals. In particular, the measured pressure variation in the region of the bristle tips was significant The deflection of the bristles was determined by comparing the bristle tip pressures with the static pressures along the shaft. Hence the compaction of the pack in this region was found directly. A numerical modelling of brush seals employing anisotropic flow resistance has been developed. Predictions were compared with the measured pressure distributions within the pack. This enabled sensible selection of the pack resistance distribution to be made. Although uniform anisotropic resistance throughout the pack gave reasonable flow rate characteristics, the pressure distribution was not reproduced. A variation of resistance coefficient consistent with the observed compaction was required to give a solution comparable with the experiments.
Chew JW, Doherty JW, Gillan M, Hills NJ (2006) practical applications of automated design and optimisation techniques using CFD,
Application of design optimisation techniques using CFD to problems for turbomachinery internal air systems and motorsport will be described and discussed. Developments in these areas build on earlier work on turbomachinery blade and aircraft applications, and present new challenges. Specific examples include turbine cooling air pre-swirl nozzles, turbine rim sealing, and full track optimisation of a Champ Car. Focussing on these specific examples, issues such as choice of optimisation method, automation of mesh generation, geometry parameterisation, solution convergence, model accuracy and method robustness will be considered.
Sun Z, Chew JW, Hills NJ, Lewis L, Mabilat C (2010) COUPLED AERO-THERMO-MECHANICAL SIMULATION FOR A TURBINE DISC THROUGH A FULL TRANSIENT CYCLE, PROCEEDINGS OF THE ASME TURBO EXPO 2010, VOL 4, PTS A AND B pp. 1025-1036 AMER SOC MECHANICAL ENGINEERS
CHEW JW (1991) A THEORETICAL-STUDY OF INGRESS FOR SHROUDED ROTATING-DISK SYSTEMS WITH RADIAL OUTFLOW, JOURNAL OF TURBOMACHINERY-TRANSACTIONS OF THE ASME 113 (1) pp. 91-97 ASME-AMER SOC MECHANICAL ENG
Sun Z, Chew JW, Hills NJ, Barnes CJ, Valencia AG (2012) 3D coupled fluid-solid thermal simulation of a turbine disc through a transient cycle, Proceedings of the ASME Turbo Expo 4 (PARTS A AND B) pp. 1959-1969
Thermal analysis of a turbine disc through a transient test cycle is demonstrated using 3D computational fluid dynamics (CFD) modeling for the cooling flow and 3D finite element analysis (FEA) for the disc. The test case is a 3D angular sector of the high pressure (HP) turbine assembly of a civil jet engine and includes details of the coolant flow around the blade roots. Proprietary FEA and CFD solvers are used to simulate the metal and fluid domains, respectively. Coupling is achieved through an iterative loop with smooth exchange of information between the FEA and CFD simulations at each time step, ensuring consistency of temperature and heat flux on the coupled interfaces between the metal and fluid domains. The coupled simulation can be completed within a few weeks using a PC cluster with multiple parallel CFD executions. The FEA/CFD coupled result agrees well with corresponding rig test data and the baseline 3D and 2D FEA solutions, which have been calibrated using test data. Provision of upstream boundary conditions and modeling of rapid transients are identified as areas of uncertainty. Averaging of CFD solutions and relaxation is used to overcome difficulties caused by CFD oscillations associated with flow unsteadiness. The present work supports the continued use and development of the FEA/CFD coupling method for industrial applications. Copyright © 2012 by ASME.
Chew JW (1985) Prediction of flow in a rotating cavity with radial outflow using a mixing length turbulence model, Proc. Lam. and Turb. Flow Conference pp. 318-329 Pineridge Press
May D, Chew JW, Scanlon TJ (2013) Prediction of Deswirled Radial Inflow in Rotating Cavities With Hysteresis, JOURNAL OF TURBOMACHINERY-TRANSACTIONS OF THE ASME 135 (4) ARTN 041025 ASME
Lott PT, Hills NJ, Chew JW, Scanlon T, Shahpar S (2009) HIGH PRESSURE TURBINE STAGE ENDWALL PROFILE OPTIMISATION FOR PERFORMANCE AND RIM SEAL EFFECTIVENESS, PROCEEDINGS OF ASME TURBO EXPO 2009, VOL 7, PTS A AND B pp. 1075-1087 AMER SOC MECHANICAL ENGINEERS
Chen LH, Wood PE, Jones TV, Chew JW (1999) An iterative CFD and mechanical brush seal model and comparison with experimental results, JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER-TRANSACTIONS OF THE ASME 121 (4) pp. 656-662 ASME-AMER SOC MECHANICAL ENG
Lewis L, Chew J, Woodley I, Colbourne J, Pond K (2015) The application of computational fluid dynamics and small-scale physical models to assess the effects of operational practices on the risk to public health within large indoor swimming pools, JOURNAL OF WATER AND HEALTH 13 (4) pp. 939-952 IWA PUBLISHING
Chew JW, Marshall JG, Vahdati M, Imregun M (1998) Part-speed flutter analysis of a wide-chord fan blade, UNSTEADY AERODYNAMICS AND AEROELASTICITY OF TURBOMACHINES pp. 707-724 SPRINGER
Hills N, Chew J, Turner A (2001) Computational and mathematical modelling of turbine rim seal ingestion, Proceedings of the ASME Turbo Expo 3
Understanding and modelling of main annulus gas ingestion through turbine rim seals is considered and advanced in this paper. Unsteady 3-dimensional computational fluid dynamics (CFD) calculations and results from a more elementary model are presented and compared with experimental data previously published by Hills et al (1997). The most complete CFD model presented includes both stator and rotor in the main annulus and the inter-disc cavity. The k-µ model of turbulence with standard wall function approximations is assumed in the model which was constructed in a commercial CFD code employing a pressure correction solution algorithm. It is shown that considerable care is needed to ensure convergence of the CFD model to a periodic solution. Compared to previous models, results from the CFD model show encouraging agreement with pressure and gas concentration measurements. The annulus gas ingestion is shown to result from a combination of the stationary and rotating circumferential pressure asymmetries in the annulus. Inertial effects associated with the circumferential velocity component of the flow have an important effect on the degree of ingestion. The elementary model used is an extension of earlier models based on orifice theory applied locally around the rim seal circumference. The new model includes a term accounting for inertial effects. Some good qualitative and fair quantitative agreement with data is shown. Copyright © 2001 by ASME.
Guardino C, Chew JW (2005) Numerical simulation of three-dimensional bristle bending in brush seals, JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER-TRANSACTIONS OF THE ASME 127 (3) pp. 583-591 ASME-AMER SOC MECHANICAL ENG
Javiya U, Chew J, Hills N, Dullenkopf K, Scanlon T (2012) Evaluation of CFD and coupled fluid-solid modelling for a direct transfer pre-swirl system, Proceedings of the ASME Turbo Expo 4 (PARTS A AND B) pp. 2179-2190
The prediction of the pre-swirl cooling air delivery and disc metal temperature are important for the cooling system performance and the rotor disc thermal stresses and life assessment. In this paper, standalone 3D steady and unsteady CFD, and coupled FE-CFD calculations are presented for prediction of these temperatures. CFD results are compared with previous measurements from a direct transfer pre-swirl test rig. The predicted cooling air temperatures agree well with the measurement, but the nozzle discharge coefficients are under predicted. Results from the coupled FE-CFD analyses are compared directly with thermocouple temperature measurements and with heat transfer coefficients on the rotor disc previously obtained from a rotor disc heat conduction solution. Considering the modelling limitations, the coupled approach predicted the solid metal temperatures well. Heat transfer coefficients on the rotor disc from CFD show some effect of the temperature variations on the heat transfer coefficients. Reasonable agreement is obtained with values deduced from the previous heat conduction solution. Copyright © 2012 by ASME.
Farthing PR, Chew JW, Owen JM (1989) Use of De-swirl nozzles to reduce the pressure drop in a rotating cavity with a radial inflow, American Society of Mechanical Engineers (Paper)
A combined theoretical and experimental study is described in which de-swirl nozzles were used to reduce the radial pressure drop in a rotating cavity with a radial inflow of air. The nozzles, which were attached to the outer part of the cavity, were angled such that the angular speed of the air at inlet could be in the opposite direction to that of the cavity. Solutions of the momentum-integral equations were used to predict the resulting radial distributions of pressure throughout the cavity. Flow visualization was used to confirm the flow structure, and transducers attached to one of the rotating disks in the cavity were used to measure the radial pressure distributions. The measured pressures are in good agreement with the predicted values, and the pressure drop across the cavity can be significantly less than that associated with solid-body rotation.
Chew J (2009) USE OF CFD FOR THERMAL COUPLING IN AEROENGINE
INTERNAL AIR SYSTEMS APPLICATIONS,
Fluid Machinery and Fluid Mechanics 2009 pp. 399-404 Springer Berlin Heidelberg
With the rapid progress of computational fluid dynamics (CFD) and computer technology, CFD has been increasingly used
for aero-engine component temperature predictions. This paper presents a review of the latest progress in this aspect with
emphasis on internal air system applications. The thermal coupling methods discussed include the traditional finite element
analysis (FEA), the conjugate heat transfer, FEA/CFD coupling procedure and other thermal coupling techniques. Special
attention is made to identify the merits and disadvantages between the various methodologies. Discussion is further extended
on the steady and transient thermal coupling applications.
Hills NJ, Chew JW, Turner AB (2002) Computational and mathematical modeling of turbine rim seal ingestion, Journal of Turbomachinery 124 (2) pp. 306-315
Understanding and modeling of main annulus gas ingestion through turbine rim seals is considered and advanced in this paper. Unsteady three-dimensional computational fluid dynamics (CFD) calculations and results from a more elementary model are presented and compared with experimental data previously published by Hills et al. (1997). The most complete (CFD) model presented includes both stator and rotor in the main annulus and the interdisk cavity. The k-µ model of turbulence with standard wall function approximations is assumed in the model which was constructed in a commercial CFD code employing a pressure correction solution algorithm. It is shown that considerable care is needed to ensure convergence of the CFD model to a periodic solution. Compared to previous models, results from the CFD model show encouraging agreement with pressure and gas concentration measurements. The annulus gas ingestion is shown to result from a combination of the stationary and rotating circumferential pressure asymmetries in the annulus. Inertial effects associated with the circumferential velocity component of the flow have an important effect on the degree of ingestion. The elementary model used is an extension of earlier models based on orifice theory applied locally around the rim seal circumference. The new model includes a term accounting for inertial effects. Some good qualitative and fair quantitative agreement with data is shown.
Chew JW, Hills NJ (2009) Computational fluid dynamics and virtual aeroengine modelling, PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART C-JOURNAL OF MECHANICAL ENGINEERING SCIENCE 223 (12) pp. 2821-2834 PROFESSIONAL ENGINEERING PUBLISHING LTD
Chew JW (1996) Analysis of the oil film on the inside surface of an aero-engine bearing chamber housing, ASME paper 96-GT-300
Knowledge of the flow and heat transfer in bearing chambers is important in the design of engine oil systems. In this paper a simplified model of the oil film on the housing of a bearing chamber is presented and results compared with other workers' measurements. An integral approach is used and the analysis includes the effects of surface friction, heat transfer, gravity and swirl of the oil at inlet. Two-dimensionality is assumed with variations in the axial direction being neglected. The model is expected to apply at high rotational speeds where "rimming" dominates with oil flowing round the drum in a continuous film. A similar rimming flow regime occurs in a rotating, horizontal drum partially filled with liquid and the present model is also tested against data for this problem.

Some good qualitative and quantitative agreement with measurements has been found, but significant discrepancies and uncertainties remain. Overall the results of this first attempt to analyse the bearing chamber flow are considered very encouraging.

CHEW JW (1993) A MOMENTUM-INTEGRAL SOLUTION FOR FLOW IN A ROTATING CIRCULAR DUCT, INTERNATIONAL JOURNAL OF HEAT AND FLUID FLOW 14 (3) pp. 240-245 BUTTERWORTH-HEINEMANN
Gopal V, Whiting MJ, Chew JW, Mills S (2013) Thermal contact conductance and its dependence on load cycling, International Journal of Heat and Mass Transfer 66 pp. 444-450
Heat transfer between contacting surfaces is an important factor in the thermal behaviour of engineering components in turbomachinery and various other areas of technology. Thermal contact conductance (TCC) is a parameter that quantifies this heat flow. Any theoretical prediction of TCC should take into account the effects, if any, introduced by repeated loading and unloading. This study aims to add to the limited volume of work available on this topic in the literature. In particular, the focus of this investigation is machined surfaces that typify the mating surfaces in some turbomachinery applications. Experimental work investigating the effect of loading and unloading history for numerous cycles is presented. An instrumented split tube with in line washers, loaded and unloaded under carefully controlled conditions, was used to measure the TCC of washers made of nickel alloy PE16 and 316 stainless steel. The study also examines the load cycle effect on TCC for a variety of interface surface geometries and pressures that are relevant to turbomachinery applications. The results show that load cycling, beyond the first cycle, has a minimal effect on TCC, in disagreement with other studies in the literature. This observation is seen for variety of surface topographies and maximum contact pressures. © 2013 Elsevier Ltd. All rights reserved.
CHEW JW (1988) THE EFFECT OF HUB RADIUS ON THE FLOW DUE TO A ROTATING-DISK, JOURNAL OF TURBOMACHINERY-TRANSACTIONS OF THE ASME 110 (3) pp. 417-418 ASME-AMER SOC MECHANICAL ENG
Chew J, Robins A (2010) Guest Editorial: Special section on engineering in a changing climate, PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART C-JOURNAL OF MECHANICAL ENGINEERING SCIENCE 224 (3) pp. I-II
CHEW JW (1984) PREDICTION OF FLOW IN ROTATING-DISK SYSTEMS USING THE K-EPSILON-TURBULENCE MODEL, MECHANICAL ENGINEERING 106 (8) pp. 82-82 ASME-AMER SOC MECHANICAL ENG
Wang Z, Ireland PT, Kohler ST, Chew JW (1998) Heat transfer measurements to a gas turbine cooling passage with inclined ribs, JOURNAL OF TURBOMACHINERY-TRANSACTIONS OF THE ASME 120 (1) pp. 63-69 ASME-AMER SOC MECHANICAL ENG
DADKHAH S, TURNER A, Chew J (1992) PERFORMANCE OF RADIAL CLEARANCE RIM SEALS IN UPSTREAM AND DOWNSTREAM ROTOR-STATOR WHEELSPACES, JOURNAL OF TURBOMACHINERY-TRANSACTIONS OF THE ASME 114 (2) pp. 439-445 ASME-AMER SOC MECHANICAL ENG
Hutcheson PS, Chew JW, Thorpe RB, Young C (2008) ASSESSMENT OF MODELS FOR LIQUID JET BREAKUP, PROCEEDINGS OF THE ASME TURBO EXPO 2008, VOL 4, PTS A AND B pp. 1517-1529 AMER SOC MECHANICAL ENGINEERS
Chew J (2011) Editorial, Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 225 (11) pp. 2479-2480
Chew J, Robins A (2010) Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science: Guest Editorial, Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 224 (3)
Chew JW, Hogg SI (1997) Porosity modeling of brush seals, JOURNAL OF TRIBOLOGY-TRANSACTIONS OF THE ASME 119 (4) pp. 769-775 ASME-AMER SOC MECHANICAL ENG
Javiya U, Chew J, Hills N, Dullenkopf K, Scanlon T (2013) Evaluation of computational fluid dynamics and coupled fluid-solid modeling for a direct transfer preswirl system, Journal of Engineering for Gas Turbines and Power 135 (5)
The prediction of the preswirl cooling air delivery and disk metal temperature are important for the cooling system performance and the rotor disk thermal stresses and life assessment. In this paper, standalone 3D steady and unsteady computation fluid dynamics (CFD), and coupled FE-CFD calculations are presented for prediction of these temperatures. CFD results are compared with previous measurements from a direct transfer preswirl test rig. The predicted cooling air temperatures agree well with the measurement, but the nozzle discharge coefficients are under predicted. Results from the coupled FE-CFD analyses are compared directly with thermocouple temperature measurements and with heat transfer coefficients on the rotor disk previously obtained from a rotor disk heat conduction solution. Considering the modeling limitations, the coupled approach predicted the solid metal temperatures well. Heat transfer coefficients on the rotor disk from CFD show some effect of the temperature variations on the heat transfer coefficients. Reasonable agreement is obtained with values deduced from the previous heat conduction solution. © 2013 by ASME.
MAY NE, CHEW JW, JAMES PW (1994) CALCULATION OF TURBULENT-FLOW FOR AN ENCLOSED ROTATING CONE, JOURNAL OF TURBOMACHINERY-TRANSACTIONS OF THE ASME 116 (3) pp. 548-554 ASME-AMER SOC MECHANICAL ENG
Lelli D, Chew JW, Cooper P (2006) Combined three-dimensional fluid dynamics and mechanical modeling of brush seals, JOURNAL OF TURBOMACHINERY-TRANSACTIONS OF THE ASME 128 (1) pp. 188-195 ASME-AMER SOC MECHANICAL ENG
Lapworth BL, Chew JW (1990) Numerical study of the influence of disc geometry on the flow and heat transfer in a rotating cavity, American Society of Mechanical Engineers (Paper)
Numerical solutions of the Reynolds-averaged Navier-Stokes equations have been used to model the influence of cobs and a bolt cover on the flow and heat transfer in a rotating cavity with an imposed radial outflow of air. Axisymmetric turbulent flow is assumed using a mixing length turbulence model. Calculations for the non-plane discs are compared with plane disc calculations and also with the available experimental data. The calculated flow structures show good agreement with the experimentally observed trends. For the cobbed and plane discs, Nusselt numbers are calculated for a combination of flow rates and rotational speeds; these show some discrepancies with the experiments, although the calculations exhibit the more consistent trend.
Chew JW, Farthing PR, Owen JM, Stratford B (1989) Use of fins to reduce the pressure drop in a rotating cavity with a radial inflow, Journal of Turbomachinery 111 (3) pp. 349-356
A combined theoretical and experimental study of radial inflow through a rotating cavity is reported. It is shown that radial fins attached to one of the disks are effective in reducing the pressure drop across the cavity. The mathematical model is an extension of earlier plane-disk momentum-integral methods, the fins are treated as rectangular rib elements and a rough-disk model is derived. Numerical solutions of the integral equations are given. An approximation linear solution is also derived. Experiments were conducted when both disks were plane and when one of the disks was fitted with 60 radial fins. Flow visualization revealed the flow structure in the cavity and confirmed some of the assumptions used in the theoretical model.
Chew JW, Hills NJ, Turner AB, Khalatov S, Scanlon T (2003) Measurement and analysis of flow in a pre-swirled cooling air delivery system, American Society of Mechanical Engineers, International Gas Turbine Institute, Turbo Expo (Publication) IGTI 5 B pp. 913-920
Measurements and analysis for a pre-swirl cooling air delivery system are reported here. The experimental rig used is representative of aero-engine conditions, having 18 pre-swirl nozzles, 72 receiver holes, capable of speeds up to 11 000 rpm, and giving differences between total temperature upstream of the pre-swirl nozzles and relative total temperature measured in the receiver holes of up to 26K. Pressure and temperature measurements are reported. An elementary model is developed for calculation of the cooling air delivery temperature. This accounts for the pre-swirl nozzle velocity coefficient, moments on the stationary and rotating surfaces in the pre-swirl chamber, and flows through the inner and outer seals to the chamber. The model is shown to correlate the measurements well for a range of disc speeds and pre-swirl velocity to disc speed ratios.
Chew JW (1989) A theoretical study of ingress for shrouded rotating disc systems with radial outflow, Proceedings of the ASME Turbo Expo 1
Copyright © 1989 by ASME.Sealing of the cavity formed between a stationary disc and a rotating disc under axisymmetric conditions is considered. A mathematical model of the flow in the cavity based on momentum integral methods is described and this is coupled to a simple model of the seal for the case when no ingress occurs. Predictions of the minimum imposed flow required to prevent ingress are obtained and shown to be in reasonable agreement with the data of Bayley and Owen (1970), Owen and Phadke (1982), Phadke (1982), and Phadke and Owen (1982, 1983, 1988). With an empirical constant in the model chosen to match this data predictions for the minimum sealing flow are shown to be in good agreement with Graber et al's (1987) measurements. The analysis of Phadke's data also indicates the measurements for small seal clearances must be viewed with caution due to errors in setting the seal clearance. These errors are estimated to be twice the minimum clearance considered. Seal behaviour when ingress occurs is also considered and estimates of the amount of ingress are made from the available data.
Chew JW (1987) COMPUTATION OF FLOW AND HEAT TRANSFER IN ROTATING DISC SYSTEMS., 2nd ASME-JSME Thermal Engineering Conference 3 pp. 361-367
Boudet J, Autef VND, Chew JW, Hills NJ, Gentilhomme O (2005) Numerical simulation of rim seal flows in axial turbines, AERONAUTICAL JOURNAL 109 (1098) pp. 373-383 ROYAL AERONAUTICAL SOC
Chew JW, Vahdati M, Imregun M (1998) Predicted influence of intake acoustics upon part-speed fan flutter, American Society of Mechanical Engineers (Paper) (GT)
While it is known that the occurrence of flutter is dominated by aerodynamics, it also depends on such parameters as inlet distortion and acoustics, aerodynamic and mechanical mistuning, and structural damping. It is shown in this paper that recent developments in predictive methods are showing considerable promise and leading to an improved understanding of the controlling parameters. A non-linear coupled structural-fluid approach is described and applied at engine representative conditions. This involves 3D unsteady CFD calculations of the fan and intake flows. Particular emphasis is placed on the influence of intake acoustics. Earlier work on flutter prediction has focused on either the fan assembly without a proper representation of the intake, or the calculation of the acoustic properties of the intake without properly representing the interaction with the fan. The present study includes a combined fan plus intake calculation, the latter being represented via an axisymmetric approximation. With an initial prescribed velocity disturbance of the blades in a 2 nodal diameter mode, the calculations showed a strong response in a 4 nodal diameter mode. Considerable acoustic activity within the duct was also noted. This result was compared with CFD calculations for the full 3D intake geometry. It was concluded that a realistic representation of intake acoustics is required for a full description of the problem.
May D, Chew JW (2014) A MODEL FOR THE TRANSIENT BEHAVIOR OF VORTEX AMPLIFIERS, PROCEEDINGS OF THE ASME TURBO EXPO: TURBINE TECHNICAL CONFERENCE AND EXPOSITION, 2014, VOL 5C AMER SOC MECHANICAL ENGINEERS
Chew JW, Hamby RJ, Marshall JG, Vahdati M (1999) Part speed flutter of transonic fans, RTO meeting proceedings 8, RTO-MP-8 AC/323(AVT)TP/9 pp. 26-1-26-10 NATO
Until recently only rudimentary methods have been available to assess designs for susceptibility to part speed flutter, but progress is now being made with more advanced CFD-based models. Earlier work has shown that coupled structural-fluid, non-linear methods may usefully be applied to this problem, but have also indicated that more computationally efficient linear methods have a role. One such linear approach is described in this paper and demonstrated on two research fans, representative of civil and military engines. Calculations are consistent with experimental observations in that the civil fan was found susceptible to flutter while the military fan was not. The results confirm the utility of the linear approach and give further insight into the physics of this type of flutter.
Woodland S, Crocombe AD, Chew JW, Mills SJ (2011) A New Method for Measuring Thermal Contact Conductance-Experimental Technique and Results, JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER-TRANSACTIONS OF THE ASME 133 (7) ARTN 071601 ASME-AMER SOC MECHANICAL ENG
Chew J, Dadkhah S, Turner A (1991) Rim sealing of rotor-stator wheelspaces in the absence of external flow, American Society of Mechanical Engineers (Paper)
Sealing of the cavity formed between a rotating disc and a stator in the absence of a forced external flow is considered. In this circumstances the pumping action of the rotating disc may draw fluid into the cavity through the rim seal. Minimum cavity throughflow rates required to prevent such ingress are estimated experimentally and from a mathematical model. The results are compared with other worker's measurements. Measurements for three different types of rim seal are reported for a range of seal clearances and for rotational Reynolds numbers up to 3 × 106. The mathematical model is found to correlate the experimental data reasonably well.
CHEW JW (1984) DEVELOPMENT OF A COMPUTER-PROGRAM FOR THE PREDICTION OF FLOW IN A ROTATING CAVITY, INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS 4 (7) pp. 667-683 JOHN WILEY & SONS LTD
Pitz DB, Chew JW (2015) Numerical simulation of natural convection in a differentially heated tall enclosure using a spectral element method,
Natural convection in differentially heated enclosures is a benchmark problem used to investigate the physics of buoyant flows and to validate numerical methods. Such configurations are also of interest in engineering applications such as cooling of electronic components and air flow around buildings. In this work a spectral element method is used to carry out direct numerical simulations of natural convection in a tall enclosure of aspect ratio 4 with isothermal vertical walls and adiabatic horizontal walls. Spectral element methods combine the flexibility of classical finite element methods with the high accuracy and efficiency of single-domain spectral methods. The flow is solved in a three-dimensional
domain with periodic boundary conditions imposed in the third direction. The numerical results are compared with solutions available in the literature and with numerical results obtained using a commercial software that employs a low-order finite volume method. Good agreement with previous work is obtained for the value of the Rayleigh number investigated, Ra = 2E9, which is greater than the critical value of Ra where transition to an unsteady, chaotic state is known to occur. The results are presented in terms of the time-averaged flow structure, Reynolds stresses and modal energies. Although the time-averaged velocity and temperature fields obtained with a commercial finite volume code are in general good agreement with the results obtained with the spectral element code, it does not give accurate predictions of second-order statistics.
FARTHING PR, CHEW JW, OWEN JM (1991) THE USE OF DESWIRL NOZZLES TO REDUCE THE PRESSURE-DROP IN A ROTATING CAVITY WITH A RADIAL INFLOW, JOURNAL OF TURBOMACHINERY-TRANSACTIONS OF THE ASME 113 (1) pp. 106-114 ASME-AMER SOC MECHANICAL ENG
LAPWORTH BL, CHEW JW (1992) A NUMERICAL STUDY OF THE INFLUENCE OF DISK GEOMETRY ON THE FLOW AND HEAT-TRANSFER IN A ROTATING CAVITY, JOURNAL OF TURBOMACHINERY-TRANSACTIONS OF THE ASME 114 (1) pp. 256-263 ASME-AMER SOC MECHANICAL ENG
Javiya U, Chew J, Hills N, Scanlon T (2015) Coupled FE-CFD Thermal Analysis for a Cooled Turbine DisK, PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART C-JOURNAL OF MECHANICAL ENGINEERING SCIENCE Sage
This paper presents transient aero-thermal analysis for a gas turbine disk and the surrounding air flows through a transient slam acceleration/deceleration ?square cycle? engine test, and compares predictions with engine measurements. The transient solid-fluid interaction calculations were performed with an innovative coupled finite element (FE) and computational fluid dynamics (CFD) approach. The computer model includes an aero-engine high pressure turbine (HPT) disk, adjacent structure, and the surrounding internal air system cavities. The model was validated through comparison with the engine temperature measurements and is also compared with industry standard standalone FE modelling. Numerical calculations using a 2D FE model with axisymmetric and 3D CFD solutions are presented and compared. Strong coupling between CFD solutions for different air system cavities and the FE solid model led to some numerical difficulties. These were addressed through improvement to the coupling algorithm. Overall performance of the coupled approach is very encouraging giving temperature predictions as good as a traditional model that had been calibrated against engine measurements.
Farthing PR, Chew JW, Owen JM (1989) The use of de-swirl nozzles to reduce the pressure drop in a rotating cavity with a radial inflow, Proceedings of the ASME Turbo Expo 1
Copyright © 1989 by ASME.A combined theoretical and experimental study is described in which de-swirl nozzles were used to reduce the radial pressure drop in a rotating cavity with a radial inflow of air. The nozzles, which were attached to the outer part of the cavity, were angled such that the angular speed of the air at inlet could be in the opposite direction to that of the cavity. Solutions of the momentum-integral equations were used to predict the resulting radial distributions of pressure throughout the cavity. Flow visualization was used to confirm the flow structure, and transducers attached to one of the rotating discs in the cavity were used to measure the radial pressure distributions. Results are presented for 'swirl fractions' (that is, the ratio of the angular speed of the air leaving the nozzles to that of the cavity) in the range -0.4 to + 0.9, and for 0.01 w | ReÆ-0-8w and ReÆ are the nondimensional flow rate and rotational Reynolds number, respectively. The measured pressures are in good agreement with the predicted values, and the pressure drop across the cavity can be significantly less than that associated with solid-body rotation. The flow rate produced by the pressure drop across the cavity is not unique: there are up to three possible values of flow rate for any given value of pressure drop.
Chew JW, Ciampoli F, Hills NJ, Scanlon T (2005) Pre-swirled cooling air delivery system performance, Proceedings of the ASME Turbo Expo 2005, Vol 3 Pts A and B pp. 1129-1137 AMER SOC MECHANICAL ENGINEERS
Boudet J, Hills NJ, Chew JW (2006) Numerical simulation of the flow interaction between turbine main annulus and disc cavities, Proceedings of the ASME Turbo Expo 6 PART A pp. 553-562
This paper presents numerical simulations of the unsteady flow interactions between the main annulus and the disc cavity for an axial turbine. The simulations show the influence of the main annulus asymmetries (vane wakes, blade potential effect), and the appearance of rim seal flow instabilities. The generation of secondary frequencies due to non-linear interactions is observed, and the possibility of further low frequency effects and resonance is noted. The computations are compared to experimental results, looking at tracer gas concentration and mass-flows. Results are further analysed to investigate the influence of the rim seal flow on the blading aerodynamics. The flow that is ejected through the rim seal influences the unsteady flow impinging the blades. The influence of this rim-seal flow is even observed downstream of the blades, where it distorts the radial profile of stagnation temperature. Copyright © 2006 by ASME.
Kilfoil ASR, Chew JW (2009) Modelling of buoyancy-affected flow in co-rotating disc cavities, Proceedings of the ASME Turbo Expo 3 pp. 1113-1122
Research in rotational buoyancy-driven flow has shown that the flow within the compressor inter-disc cavities is highly three-dimensional and time dependent. Two approaches in the numerical modelling of the flow have been considered. One is to use 3D, unsteady CFD to model a single inter-disc cavity with axial throughflow. This is very computationally expensive. A second approach, adopted here, is to break down the complex flow process into separate physical mechanisms and introduce approximate but computationally efficient models for these processes. The aim is to produce a method that can be incorporated into current design practice. Two underlying flow mechanisms may be identified for this complex flow; the first associated with the flow within the inter-disc cavities and the second associated with the axial throughflow under the compressor disc bores. Using CFD, the modelling of these two underlying flow mechanisms has been combined and a steady axisymmetric modelling method has been developed. The technique has been applied to both a research compressor rig and to an actual gas turbine HP compressor rotor, and results have been compared to measured data.
Chew JW, Hills NJ, Hornsby C, Young C (2003) Recent developments in application of CFD to turbomachinery internal air systems, Proc. 5th European Turbomachinery Conference
Advances in the development and application of computational fluid dynamics (CFD) to gas turbine internal air systems are discussed in this paper. It is shown that the combination of parallel computation, using powerful PC clusters, with relatively robust and flexible CFD solvers is now having considerable impact in industry. At the same time research studies demonstrate that capability continues to expand. Examples are given of 3D, steady and unsteady industrial applications, with discussions of computing times on PC clusters using both ethernet and myrinet network connections. Integration of CFD into the design process is also considered. Research studies, centring on model validation and methods improvement are also illustrated and discussed, with inclusion of very recent work using a 32 processor cluster with fast myrinet networking.
Ciampoli F, Chew JW, Shahpar S, Willocq E (2007) Automatic optimization of preswirl nozzle design, JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER-TRANSACTIONS OF THE ASME 129 (2) pp. 387-393 ASME-AMER SOC MECHANICAL ENG
Volkov KN, Hills NJ, Chew JW (2008) SIMULATION OF TURBULENT FLOWS IN TURBINE BLADE PASSAGES AND DISC CAVITIES, PROCEEDINGS OF THE ASME TURBO EXPO 2008, VOL 4, PTS A AND B pp. 1543-1554 AMER SOC MECHANICAL ENGINEERS
May D, Chew JW (2010) RESPONSE OF A DISK CAVITY FLOW TO GAS TURBINE ENGINE TRANSIENTS, PROCEEDINGS OF THE ASME TURBO EXPO 2010, VOL 4, PTS A AND B pp. 1113-1122 AMER SOC MECHANICAL ENGINEERS
Lewis L, Chew J, Woodley I, Colbourne J, Pond K (2015) Modifications for water management guidance based on an assessment of swimming pool water consumption of an operational facility in the UK, WATER SCIENCE AND TECHNOLOGY-WATER SUPPLY 15 (5) pp. 965-973 IWA PUBLISHING
Gentilhomme O, Hills N, Turner A, Chew J (2002) Measurement and analysis of ingestion through a turbine rim seal, American Society of Mechanical Engineers, International Gas Turbine Institute, Turbo Expo (Publication) IGTI 3 B pp. 925-934
Experimental measurements from a new single stage turbine are presented. The turbine has 26 vanes and 59 rotating blades with a design point stage expansion ratio of 2.5 and vane exit Mach number of 0.96. A variable sealing flow is supplied to the disc cavity upstream of the rotor and then enters the annulus through a simple axial clearance seal situated on the hub between the stator and rotor. Measurements at the annulus hub wall just downstream of the vanes show the degree of circumferential pressure variation. Further pressure measurements in the disc cavity indicate the strength of the swirling flow in the cavity, and show the effects of mainstream gas ingestion at low sealing flows. Ingestion is further quantified through seeding of the sealing air with nitrous oxide or carbon dioxide and measurement of gas concentrations in the cavity. Interpretation of the measurements is aided by steady and unsteady computational fluid dynamics solutions, and comparison with an elementary model of ingestion.
Vinod Kumar B, Chew J, Hills NJ (2012) Rotating flow and heat transfer in cylindrical cavities with radial inflow, Proceedings of the ASME Turbo Expo 4 (PARTS) pp. 2047-2060
Design and optimization of an efficient internal air system of a gas turbine requires thorough understanding of the flow and heat transfer in rotating disc cavities. The present study is devoted to numerical modelling of flow and heat transfer in a cylindrical cavity with radial inflow and comparison with the available experimental data. The simulations are carried out with axi-symmetric and 3-D sector models for various inlet swirl and rotational Reynolds numbers upto 2.1×106. The pressure coefficients and Nusselt numbers are compared with the available experimental data and integral method solutions. Two popular eddy viscosity models, the Spalart-Allmaras and the k-e , and a Reynolds stress model have been used . For cases with particularly strong vortex behaviour the eddy viscosity models show some shortcomings with the Spalart-Allmaras model giving slightly better results than the k-e model. Use of the Reynolds stress model improved the agreement with measurements for such cases. The integral method results are also found to agree well with the measurements. Copyright © 2012 by ASME.
Chew JW, Snell RJ (1988) Prediction of the pressure distribution for radial inflow between co-rotating discs, Proceedings of the ASME Turbo Expo 1
Copyright © 1988 by ASME.The problem of radial inflow between two plane co-rotating discs with the angular velocity of the fluid at inlet equal to that of the discs is considered. An integral solution technique for turbulent flow, based on that of von Karman (1921), is described. Solutions are shown to be in good agreement with most of the available experimental data. For incompressible flow the pressure drop coefficient is a function of just two non-dimensional parameters; the radius ratio for the cavity and a throughflow parameter. For air flows compressibility can be important and an additional non-dimensional parameter is needed. Results for a wide range of conditions are presented graphically. These show the sensitivity of the pressure coefficient to the governing parameters and provide a quick method for estimating the pressure drop.
Young C, Chew JW (2005) Evaluation of the volume of fluid modelling approach for simulation of oil/air system flows, Proceedings of the ASME Turbo Expo 2005, Vol 3 Pts A and B pp. 1249-1257 AMER SOC MECHANICAL ENGINEERS
Woodland S, Crocombe AD, Chew JW, Mills SJ (2008) A NEW METHOD FOR MEASURING THERMAL CONTACT CONDUCTANCE EXPERIMENTAL TECHNIQUE AND RESULTS, PROCEEDINGS OF THE ASME TURBO EXPO 2008, VOL 4, PTS A AND B pp. 627-634 AMER SOC MECHANICAL ENGINEERS
Chew J, Pitz DB, Marxen O, Hills N (2016) DIRECT NUMERICAL SIMULATION OF ROTATING CAVITY FLOWS USING A SPECTRAL ELEMENT-FOURIER METHOD, Proceedings of ASME Turbo Expo 2016: ASME
A high-order numerical method is employed to investigate flow in a rotor/stator cavity without heat transfer and buoyant flow in a rotor/rotor cavity. The numerical tool used employs a spectral element discretisation in two dimensions and a Fourier expansion in the remaining direction, which is periodic and corresponds to the azimuthal coordinate in cylindrical coordinates. The spectral element approximation uses a Galerkin method to discretise the governing equations, similarly to a finite element method, but employs high-order polynomials within each element to obtain spectral accuracy. A second-order, semi-implicit, stiffly stable algorithm is used for the time discretisation, and no subgrid modelling is included in the governing equations. Numerical results obtained for the rotor/stator cavity compare favourably with experimental results for Reynolds numbers up to Re1 = 106 in terms of velocities and Reynolds stresses. For the buoyancy-driven flow, the energy equation is coupled to the momentum equations via the Boussinesq approximation, which has been implemented in the code considering two different formulations. Numerical predictions of the Nusselt number obtained using the traditional Boussinesq approximation are considerably higher than available experimental data. Much better agreement is obtained when the extended Boussinesq approximation is em-ployed. It is concluded that the numerical method employed has considerable potential for further investigations of rotating cavity flows.
Ciampoli F, Chew JW, Shahpar S, Willocq E (2006) Automatic optimisation of pre-swirl nozzle design, Proceedings of the ASME Turbo Expo 2006, Vol 3, Pts A and B pp. 1345-1353 AMER SOC MECHANICAL ENGINEERS
CHEW JW (1985) EFFECT OF FRICTIONAL HEATING AND COMPRESSIVE WORK IN ROTATING AXISYMMETRICAL FLOW, JOURNAL OF HEAT TRANSFER-TRANSACTIONS OF THE ASME 107 (4) pp. 984-986 ASME-AMER SOC MECHANICAL ENG
Amirante D, Sun Z, Chew J, Hills N J, Atkins NR (2016) MODELING OF COMPRESSOR DRUM CAVITIES WITH RADIAL INFLOW, Proceedings of ASME Turbo Expo 2016
Reynolds-Averaged Navier-Stokes (RANS) computations have been conducted to investigate the ?ow and heat trans-fer between two co-rotating discs with an axial through?ow of cooling air and a radial bleed introduced from the shroud. The computational ?uid dynamics (CFD) models have been cou-pled with a thermal model of the test rig, and the predicted metal temperature compared with the thermocouple data. CFD solutions are shown to vary from a buoyancy driven regime to a forced convection regime, depending on the radial in?ow rate prescribed at the shroud. At a high radial in?ow rate, the computations show an excellent agreement with the measured temperatures through a transient rig condition. At a low radial in?ow rate, the cavity ?ow is destabilized by the thermal strati?cation. Good qualitative agreement with the measurements is shown, although a signi?cant over-prediction of disc temperatures is observed. This is associated with under prediction of the penetration of the axial through?ow into the cavity. The mismatch could be the result of strong sensitivity to the prescribed inlet conditions, in addition to possible shortcomings in the turbulence modeling.
Lelli D, Chew JW, Cooper P (2005) Combined 3D fluid dynamics and mechanical modelling of brush seals, Proceedings of the ASME Turbo Expo 2005, Vol 3 Pts A and B pp. 1207-1216 AMER SOC MECHANICAL ENGINEERS
Hanby RF, Silvester DJ, Chew JW (1996) A comparison of coupled and segregated iterative solution techniques for incompressible swirling flow, INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS 22 (5) pp. 353-373 JOHN WILEY & SONS LTD
Chew JW (1990) Prediction of rotating disc flow andheat transfer in gas turbine engines, Proc. 3rd Int. Symp. Transport Phenomena and Dynamics of Rotating Machinery pp. 145-160 Hemisphere
Motivated by the need to improve design techniques for aeroengines considerable effort has been put intodeveloping predictive techniques for rotating disc flow and heat transfer. Some notable advances have been made recently and these are reviewed here. The theoretical techniques employed include analytical solutions for laminar flow, momentum-integral methods for turbulent flow and finite difference solutions of the Reynolds-averaged Navier-stokes equations. Each of these methods is discussed and and predictive capability is illustrated through comparisons with experimental data.
VIRR GP, CHEW JW, COUPLAND J (1994) APPLICATION OF COMPUTATIONAL FLUID-DYNAMICS TO TURBINE DISK CAVITIES, JOURNAL OF TURBOMACHINERY-TRANSACTIONS OF THE ASME 116 (4) pp. 701-708 ASME-AMER SOC MECHANICAL ENG
Guardino C, Chew JW (2004) Numerical simulation of 3D bristle bending in brush seals, Proceedings of the ASME Turbo Expo 2004 4 pp. 277-288
This paper presents a new method for predicting the 3D bending behaviour of bristles in brush seals. The model builds upon and addresses shortcomings in an earlier 2D bending model. The work was motivated by the need to develop a general 3D solid mechanical model which can ultimately be incorporated into CFD models of flow and heat transfer through brush seals. The iterative method considered here, which is based upon linear beam-bending theory, allows relatively large numbers of bristles to be considered with arbitrary imposed aerodynamic forces. Bristle-to-bristle contacts and deflections are considered, as well as shaft and backing ring contacts. The method also allows arbitrary initial bristle packs and lay-angles to be considered, as well as periodic conditions so that the model represents a sector of a brush seal. Other physically important features such as the so-called '3D-splay' and 'inclined prop' effects are also taken into account. The method described here has been incorporated into a new computer code called 'SUBSIS' (Surrey University Brush Seal Iterative Simulator). Example results from this code are presented which show the bending behaviour of initially hexagonally packed brush seals under model imposed pressure loads acting on the bristle tips. The effects of rotor incursions into the bristle pack, increase of the pressure load, and changes in the lay-angle and Young's modulus are also shown. The results illustrate the expected bending behaviour observed in real brush seals. Procedures for coupling SUBSIS with CFD models are also currently under investigation.
Chew JW, Taylor IJ, Bonsell JJ (1996) CFD developments for turbine blade heat transfer, THIRD INTERNATIONAL CONFERENCE ON COMPUTERS IN RECIPROCATING ENGINES AND GAS TURBINES 1996 (1) pp. 51-64 MECHANICAL ENGINEERING PUBL
Swimming pools provide an excellent facility for exercise and leisure but are also prone to contamination from microbial pathogens. The study modelled a 50-m x 20-m swimming pool using both a small scale physical model and computational fluid dynamics to investigate how water and pathogens move around a pool in order to identify potential risk spots.
Our study revealed a number of lessons for pool operators, designers and policy makers: disinfection reaches the majority of a full scale pool in approximately 16 minutes operating at the maximum permissible inlet velocity of 0.5m/s. This suggests that where a pool is designed to have 15 paired inlets it is capable of distributing disinfectant throughout the water body within an acceptable time frame.
However, the study also showed that the exchange rate of water is not uniform across the pool tank and that there is potential for areas of the pool tank to retain contaminated water for significant periods of time. ?Dead spots? exist at either end of the pool where pathogens could remain. This is particularly significant if there is a faecal release into the pool by bathers infected with Cryptosporidium parvum, increasing the potential for waterborne disease transmission.
May D, Chew JW, Scanlon TJ (2012) Prediction of de-swirled radial inflow in rotating cavities with hysteresis, Proceedings of the ASME Turbo Expo 4 (PARTS A AND B) pp. 2037-2046
De-swirl nozzles are sometimes used in turbomachinery to reduce the pressure drop when air is drawn radially inwards through a rotating cavity. However, this can lead to non-unique steady state solutions with operating conditions achieved depending on how the steady point is approached. In the present study, a transient, 1D model of flow in a rotating cavity has been created. The model allows the vortex profile to change with through flow rate, and links this to estimates of disk windage, tangential velocity and, consequently, the vortex pressure gradient. The model was applied to the simulation of de-swirl nozzle fed, rotating cavities with radial inflow. The steady vortex flow characteristics (non-dimensional flow versus pressure ratio) predicted by the model were validated for 2 distinct cases. For a smooth rectangular cavity the flow characteristic was predicted using the model's default parameters. For an engine-representative case with nonaxisymmetric geometric features, the flow characteristic of the cavity was reproduced with some alignment of the model. The transient model reproduced experimentally observed hysteresis, discontinuity in operating characteristics, and regions where no steady-state solution could be found. A transient model is required as a steady state model would choose one of the possible solutions without physical justification. In the case of the engine-representative rig, part of the flow characteristic could not be obtained in testing. This is determined to be due to the interaction of the negative resistance region of the vortex and the flow modulating valve characteristic. Measures that allow the full capture of the flow characteristic in rig testing are identified. Copyright © 2012 by ASME.
IACOVIDES H, CHEW JW (1993) THE COMPUTATION OF CONVECTIVE HEAT-TRANSFER IN ROTATING CAVITIES, INTERNATIONAL JOURNAL OF HEAT AND FLUID FLOW 14 (2) pp. 146-154 BUTTERWORTH-HEINEMANN
CHEW JW, OWEN JM, PINCOMBE J (1984) NUMERICAL PREDICTIONS FOR LAMINAR SOURCE SINK FLOW IN A ROTATING CYLINDRICAL CAVITY, JOURNAL OF FLUID MECHANICS 143 (JUN) pp. 451-466 CAMBRIDGE UNIV PRESS
Chew JW, Rogers RH (1988) An integral method for the calculation of turbulent forced convection in a rotating cavity with radial outflow, International Journal of Heat and Fluid Flow 9 (1) pp. 37-48
The work of Owen, Pincombe, and Rogers3 makes use of integral momentum techniques to investigate the flow of an isothermal fluid in a rotating cavity with an imposed radial throughflow. This paper extends the method to include the entraining boundary layer in the source region and to include an integral energy equation to predict the temperature in the core of the fluid when the discs of the cavity are heated. The effects of fluid property variations and frictional heating are also taken into account. The effect of various approximations are discussed, and the way in which the computed heat transfer depends on the mass flow coefficient, the rotational Reynolds number and the type of disc temperature distribution is found. © 1988.
Sun Z, Chew JW, Hills NJ, Volkov KN, Barnes CJ (2008) EFFICIENT FEA/CFD THERMAL COUPLING FOR ENGINEERING APPLICATIONS, PROCEEDINGS OF THE ASME TURBO EXPO 2008, VOL 4, PTS A AND B pp. 1505-1515 AMER SOC MECHANICAL ENGINEERS
vaughan CM, Gilham S, Chew JW (1989) Numerical solutions of rotating disc flows using a non-linear multigrid algorithm., Proc. 6th Int. Conf. on Num. Methods Lam and Turb. Flow pp. 1640-1651 Pineridge Press
A finite difference solution algorithm incorporating a multigrid acceleration technique i presented, with applications to rotating disc flows. Comparisons are made to a one grid algorithm which show the multigrid scheme to be highly efficient over a wide range of test cases, including fully turbulent compressible non-isothermal flow at high rotational speed. Comparisons with previous numerical and experimental results confirm the accuracy of the current code.
CHEW JW (1985) COMPUTATION OF FORCED LAMINAR CONVECTION IN ROTATING CAVITIES, JOURNAL OF HEAT TRANSFER-TRANSACTIONS OF THE ASME 107 (2) pp. 277-282 ASME-AMER SOC MECHANICAL ENG
Marshall JG, Chew JW, Lee SJ (2000) Forced response study of distortion driven resonance in a low aspect ratio fan,
Chew J, Onori M, Amirante D, Hills N (2016) LES VALIDATION FOR A ROTATING CYLINDRICAL CAVITY WITH RADIAL INFLOW, Proceedings of ASME Turbo Expo 2016
This paper describes Large-Eddy Simulations (LES) of the flow in a rotating cavity with narrow inter-disc spacing and a radial inflow introduced from the shroud. Simulations have been conducted using a compressible, unstructured, finite-volume solver, and testing different subgrid scale models. These include the standard Smagorinsky model with Van Driest damping function near the wall, the WALE model and the implicit LES procedure. Reynolds averaged Navier-Stokes (RANS) results, based on the Spalart-Allmaras and SST k ? É models, are also presented. LES solutions reveal a turbulent source region, a laminar oscillating core with almost zero axial and radial velocity and turbulent Ekman type boundary layers along the discs. Validations are carried out against the experimental data available from the study of Firouzian et al. [1]. It is shown that the tangential velocity and the pressure drop across the cavity are very well predicted by both RANS and LES, although significant differences are observed in the velocity profiles within the boundary layers.
Ciampoli F, Hills NJ, Chew JW, Scanlon T (2008) UNSTEADY NUMERICAL SIMULATION OF THE FLOW IN A DIRECT TRANSFER PRE-SWIRL SYSTEM, PROCEEDINGS OF THE ASME TURBO EXPO 2008, VOL 4, PTS A AND B pp. 1647-1655 AMER SOC MECHANICAL ENGINEERS
Beard P, Chew J, Gao F, Chana K (2016) UNSTEADY FLOW PHENOMENA IN TURBINE RIM SEALS, ASME Journal of Engineering for Gas Turbines and Power 139 (3) 032501 ASME
While turbine rim sealing flows are an important aspect of turbomachinery design, affecting turbine aerodynamic performance and turbine disc temperatures, the present understanding and predictive capability for such flows is limited. The aim of the present study is to clarify the flow physics involved in rim sealing flows and to provide high quality experimental data for use in evaluation of CFD models. The seal considered is similar to a chute seal previously investigated by other workers, and the study focuses on the inherent unsteadiness of rim seal flows, rather than unsteadiness imposed by the rotating blades. Unsteady pressure measurements from radially and circumferentially distributed transducers are presented for flow in a rotor-stator disc cavity and the rim seal without imposed external flow. The test matrix covered ranges in rotational Reynolds number, Re?, and non-dimensional flow rate, , of 2.2 ?3.0x106 and 0 ? 3.5x103 respectively. Distinct frequencies are identified in the cavity flow and detailed analysis of the pressure data associates these with large scale flow structures rotating about the axis. This confirms the occurrence of such structures as predicted in previously published CFD studies and provides new data for detailed assessment of CFD models.
Noor Mohamed S, Chew J, Hills N (2017) Effect of bolts on flow and heat transfer in a rotor-stator disc cavity, ASME Journal of Engineering for Gas Turbines and Power 139 (5) 051901 American Society of Mechanical Engineers
Previous studies have indicated some differences between steady CFD predictions of flow in a rotor-stator disc cavity with rotating bolts compared to measurements. Recently time-dependent CFD simulations have revealed the unsteadiness present in the flow and have given improved agreement with measurements. In this paper unsteady Reynolds averaged Navier-Stokes (URANS) 3600 model CFD calculations of a rotorstator cavity with rotor bolts were performed in order to better understand the flow and heat transfer within a disc cavity previously studied experimentally by other workers. It is shown that the rotating bolts generate unsteadiness due to wake shedding which creates time-dependent flow patterns within the cavity. At low throughflow conditions, the unsteady flow significantly increases the average disc temperature. A systematic parametric study is presented giving insight into the influence of number of bolts, mass flow rate, cavity gap ratio and the bolts-to-shroud gap ratio on the time depended flow within the cavity.
Cao C, Chew J, Millington P, Hogg S (2003) Interaction of rim seal and annulus flows in an axial flow turbine, American Society of Mechanical Engineers, International Gas Turbine Institute, Turbo Expo (Publication) IGTI 5 B pp. 1011-1019
A combined computational fluid dynamics (CFD) and experimental study of interaction of main gas path and rim sealing flow is reported. The experiments were conducted on a two stage axial turbine and included pressure measurements for the cavity formed between the stage 2 rotor disc and the upstream diaphragm for two values of the diaphragm-to-rotor axial clearance. The pressure measurements indicate that ingestion of the highly swirling annulus flow leads to increased vortex strength within the cavity. This effect is particularly strong for the larger axial clearance. Results from a number of steady and unsteady CFD models have been compared to the measured results. Good agreement between measurement and calculation for time-averaged pressures was obtained using unsteady CFD models, which predicted previously unknown unsteady flow features. This led to fest response pressure transducer measurements being made on the rig, and these confirmed the CED prediction.
Cao C, Chew J, Millington P, Hogg S (2004) Interaction of rim seal and annulus flows in an axial flow turbine, JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER-TRANSACTIONS OF THE ASME 126 (4) pp. 786-793
Kumar R, Chew J, Amirante D, Murua J, Hills NJ (2017) CFD Simulation of Blade Flows With High Amplitude Pitching, Proceedings of ASME 2017: Oil and Gas Applications; Supercritical CO2 Power Cycles; Wind Energy 9 ASME
Large and flexible wind turbine blades may be susceptible to severe blade deformations coupled with dynamic stall. To advance prediction capability for this problem a general deforming mesh computational fluid dynamics (CFD) method has been developed for calculating flows with moving or deforming boundaries using an elastic spring analogy. The method has been evaluated against experimental data for flow around a pitching NACA0012 airfoil in the deep dynamic stall regime where flow is highly separated, and compared with other authors0 CFD simulations for pitching airfoil. The effects of varying the reduced frequency are also investigated. During the upstroke the present results are in generally good agreement with experiment and other CFD studies. During the downstroke some differences with experiment and other CFD models are apparent. This may be due to the sensitivity of the separated flow to modelling assumptions and experimental conditions. Overall, the degree of agreement between CFD and experiment is considered encouraging.
Gao F, Chew J, Beard P, Amirante D, Hills NJ (2017) Numerical Studies of Turbine Rim Sealing Flows on a Chute Seal Configuration, Proceedings of 12th European Conference on Turbomachinery Fluid dynamics & Thermodynamics
This paper presents CFD (computational fluid dynamics) modelling of a chute type rim seal that has been previously experimentally investigated. The study focuses on inherent large-scale unsteadiness rather than that imposed by vanes and blades or external flow. A large-eddy simulation (LES) solver is validated for a pipe flow test case and then applied to the chute rim seal rotor/stator cavity. LES, Reynolds-averaged Navier-Stokes (RANS) and unsteady RANS (URANS) models all showed reasonable agreement with steady measurements within the disc cavity, but only the LES shows unsteadiness at a similar distinct peak frequency to that found in the experiment, at 23 times the rotational frequency. However, there are some significant differences between unsteadiness predicted and the measurements, and possible causes of these are discussed.
O'Mahoney T, Hills N, Chew J, Scanlon T (2011) Large-Eddy simulation of rim seal ingestion, PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART C-JOURNAL OF MECHANICAL ENGINEERING SCIENCE 225 (C12) pp. 2881-2891 Sage
Unsteady flow dynamics in turbine rim seals are known to be complex and attempts
accurately to predict the interaction of the mainstream flow with the secondary air system cooling
flows using computational fluid dynamics (CFD) with Reynolds-averaged Navier?Stokes
(RANS) turbulence models have proved difficult. In particular, published results from RANS
models have over-predicted the sealing effectiveness of the rim seal, although their use in this
context continues to be common. Previous studies have ascribed this discrepancy to the failure to
model flow structures with a scale greater than the one which can be captured in the small-sector
models typically used. This article presents results from a series of Large-Eddy Simulations (LES)
of a turbine stage including a rim seal and rim cavity for, it is believed by the authors, the first
time. The simulations were run at a rotational Reynolds number Re ¼ 2.2 106 and a main
annulus axial Reynolds number Rex ¼ 1.3 106 and with varying levels of coolant mass flow.
Comparison is made with previously published experimental data and with unsteady RANS simulations.
The LES models are shown to be in closer agreement with the experimental sealing
effectiveness than the unsteady RANS simulations. The result indicates that the previous failure
to predict rim seal effectiveness was due to turbulence model limitations in the turbine rim seal
flow. Consideration is given to the flow structure in this region.
K
O'Mahoney T, Hills N, Chew J, Scanlon T (2010) LARGE-EDDY SIMULATION OF RIM SEAL INGESTION, PROCEEDINGS OF THE ASME TURBO EXPO 2010, VOL 4, PTS A AND B pp. 1155-1165
Unsteady flow dynamics in turbine rim seals are known to
be complex and attempts accurately to predict the interaction of
the mainstream flow with the secondary air system cooling flows
using CFD with RANS turbulence models have proved difficult.
In particular, published results from RANS models have overpredicted
the sealing effectiveness of the rim seal, although their
use in this context continues to be common. Previous authors
have ascribed this discrepancy to the failure to model flow structures
with a scale greater than can be captured in the small sector
models typically used. This paper presents results from a series
of Large-Eddy Simulations (LES) of a turbine stage including a
rim seal and rim cavity for, it is believed by the authors, the first
time. The simulations were run at a rotational Reynolds number
Re¸ = 2.2 × 106 and a main annulus axial Reynolds number
Rex = 1.3 × 106 and with varying levels of coolant mass
flow. Comparison is made with previously published experimental
data and with unsteady RANS simulations. The LES models
are shown to be in closer agreement with the experimental sealing
effectiveness than the unsteady RANS simulations. The result
indicates that the previous failure to predict rim seal effectiveness
was due to turbulence model limitations in the turbine rim seal
flow. Consideration is given to the flow structure in this region.
Sun Z, Lindblad K, Chew J, Young C (2007) LES and RANS investigations into buoyancy-affected convection in a rotating cavity with a central axial throughflow, Journal of Engineering for Gas Turbines and Power 129 (2) pp. 318-325
The buoyancy-affected flow in rotating disk cavities, such as occurs in compressor disk stacks, is known to be complex and difficult to predict. In the present work, large eddy simulation (LES) and unsteady Reynolds-averaged Navier-Stokes (RANS) solutions are compared to other workers? measurements from an engine representative test rig. The Smagorinsky-Lilly model was employed in the LES simulations, and the RNG k- turbulence model was used in the RANS modeling. Three test cases were investigated in a range of Grashof number Gr=1.87 to 7.41 108 and buoyancy number Bo=1.65 to 11.5. Consistent with experimental observation, strong unsteadiness was clearly observed in the results of both models; however, the LES results exhibited a finer flow structure than the RANS solution. The LES model also achieved significantly better agreement with velocity and heat transfer measurements than the RANS model. Also, temperature contours obtained from the LES results have a finer structure than the tangential velocity contours. Based on the results obtained in this work, further application of LES to flows of industrial complexity is recommended.
Sun Z, Lindblad K, Chew J, Young C (2006) LES and RANS investigations into buoyancy-affected convection in a rotating cavity with a central axial throughflow, Proceedings of the ASME Turbo Expo 2006, Vol 3, Pts A and B pp. 1355-1364
Gentilhomme O, Hills N, Turner A, Chew J (2003) Measurement and analysis of ingestion through a turbine rim seal, JOURNAL OF TURBOMACHINERY-TRANSACTIONS OF THE ASME 125 (3) pp. 505-512
Experimental measurements from a new single stage turbine are presented. The turbine has 26 vanes and 59 rotating blades with a design point stage expansion ratio of 2.5 and vane exit Mach number of 0.96. A variable sealing flow is supplied to the disc cavity upstream of the rotor and then enters the annulus through a simple axial clearance seal situated on the hub between the stator and rotor. Measurements at the annulus hub wall just downstream of the vanes show the degree of circumferential pressure variation. Further pressure measurements in the disc cavity indicate the strength of the swirling flow in the cavity, and show the effects of mainstream gas ingestion at low sealing flows. Ingestion is further quantified through seeding of the sealing air with nitrous oxide or carbon dioxide and measurement of gas concentrations in the cavity. Interpretation of the measurements is aided by steady and unsteady computational fluid dynamics solutions, and comparison with an elementary model of ingestion.
Sun Z, Chew J (2017) Study of a conceptual design for cooled cooling air in a Preswirl Cavity, Proceedings of the 23rd ISABE conference 2017 International Society of Air Beating Engines
To achieve enhanced cooling of hot components in the high pressure (HP) section of an aeroengine, application of cooled cooling air (CCA) has been proposed. Here a ?two row preswirl feed? arrangement is considered to accommodate the CCA, together with the uncooled cooling air (UCA) in high pressure turbine (HPT) preswirl cavity. The CCA and UCA inflows are introduced into the preswirl cavity at two different radii. Most of the cooling air leaves the preswirl cavity from the receiver holes. To assess the CCA behavior in the preswirl cavity, a definition of feeding effectiveness is introduced based on the relative total temperature at the exit of the receiver hole. The CFD investigation for the preswirl cavity was conducted in a systematic way by altering both the radial position of the receiver hole and inflows of the CCA and UCA, while keeping other conditions unchanged. It was found that the feeding effectiveness increases as the radial position of the receiver hole decreases. An optimal feeding effectiveness close to a minimum mixing condition was achieved by adjusting the CCA and UCA inflows. Unsteady CFD investigations gave a similar prediction for the overall performance of the CCA in the preswirl cavity, but with a lower feeding effectiveness compared with its steady CFD counterpart. The reduction in the feeding effectiveness was attributed to an enhanced mixing from the discrete CCA and UCA inflows and associated unsteady effects.
Pitz Diogo B., Marxen Olaf, Chew John (2017) Onset of convection induced by centrifugal buoyancy in a rotating cavity, Journal of Fluid Mechanics 826 pp. 484-502 Cambridge University Press
Flows induced by centrifugal buoyancy occur in rotating systems in which the centrifugal force is large when compared to other body forces and are of interest for geophysicists and also in engineering problems involving rapid rotation and unstable temperature gradients. In this numerical study we analyse the onset of centrifugal buoyancy in a rotating cylindrical cavity bounded by two plane, insulated disks, adopting a geometrical configuration relevant to fundamental studies of buoyancy-induced flows occurring in gas turbine?s internal air systems. Using linear stability analysis, we obtain critical values of the centrifugal Rayleigh number and corresponding critical azimuthal wavenumbers for the onset of convection for different radius ratios. Using direct numerical simulation, we integrate the solutions starting from a motionless state to which small sinusoidal perturbations are added, and show that nonlinear triadic interactions occur before energy saturation takes place. At the lowest Rayleigh number considered, the final state is a limit-cycle oscillation affected by the presence of the disks, having a spectrum dominated by a certain mode and its harmonics. We show that, for this case, the limit-cycle oscillations only develop when no-slip end walls are present. For the largest considered chaotic motion occurs, but the critical wavenumber obtained from the linear analysis eventually becomes the most energetic even in the turbulent regime.
Sun Z, Amirante D, Chew J, Hills NJ (2015) Coupled Aero-Thermal Modeling of a Rotating Cavity with Radial Inflow, Journal of Engineering for Gas Turbines and Power: Transactions of the ASME ASME
Sun Z, Chew J, Kifoil A, Hills NJ (2004) Numerical simulation of natural convection in stationary and rotating cavities, Proceedings of the ASME Turbo Expo 2004 4 pp. 381-389
In compressor inter-disc cavities with a central axial throughflow it is known that the flow and heat transfer is strongly affected by buoyancy in the centrifugal force field. As a step towards developing CFD methods for such flows, buoyancy-driven flows under gravity in a closed cube and under centrifugal force in a sealed rotating annulus have been studied. Numerical simulations are compared with the experimental results of Kirkpatrick and Bohn (1986) and Bohn et al (1993). Two different CFD codes have been used and are shown to agree for the stationary cube problem. Unsteady simulations for the stationary cube show good agreement with measurements of heat transfer, temperature fluctuations, and velocity fluctuations for Rayleigh numbers up to 2 × 10 . Similar simulations for the rotating annulus also show good agreement with measured heat transfer rates. The CFD results confirm Bohn et al's results, showing reduced heat transfer and a different Rayleigh number dependency compared to gravity-driven flow. Large scale flow structures are found to occur, at all Rayleigh numbers considered.
Fu D, Chew J, Sun Z (2014) Velocity pick-up and discharge coefficient for round orifices with cross flow at inlet, PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART C-JOURNAL OF MECHANICAL ENGINEERING SCIENCE 228 (15) pp. 2728-2737 SAGE PUBLICATIONS LTD
Gao Feng, Chew John, Beard Paul F., Amirante Dario, Hills Nicholas (2018) Large-eddy simulation of unsteady turbine rim sealing flows, International Journal of Heat and Fluid Flow 70 pp. 160-170 Elsevier
Unsteady flow phenomena unrelated to the main gas-path blading have been identified in a number of turbine rim seal investigations. This unsteadiness has significant influence on the sealing effectiveness predicted by the conventional steady RANS (Reynolds-averaged Navier?Stokes) method, thus it is important for turbine stage design and optimisation. This paper presents CFD (computational fluid dynamics) modelling of a chute type rim seal that has been previously experimentally investigated. The study focuses on inherent large-scale unsteadiness rather than that imposed by vanes and blades or external flow. A large-eddy simulation (LES) solver is validated for a pipe flow test case and then applied to the chute rim seal rotor/stator cavity. LES, RANS and unsteady RANS (URANS) models all showed reasonable agreement with steady measurements within the disc cavity, but only the LES shows unsteadiness at a similar distinct peak frequency to that found in the experiment, at 23 times the rotational frequency. The boundary layer profile within the chute rim seal clearance has been scrutinised, which may explain the improvement of LES over RANS predictions for the pressure drop across the seal. LES results show a clockwise mean flow vortex. A more detailed sketch of the rim sealing flow unsteady flow structures is established with the help of the LES results. However, there are some significant differences between unsteadiness predicted and the measurements, and possible causes of these are discussed.
Emhardt Simon, Tian Guohong, Chew John (2018) A review of scroll expander geometries and their performance, Applied Thermal Engineering 141 pp. 1020-1034 Elsevier
Scroll expanders are currently attracting interest for integration in small scale organic Rankine cycle (ORC) waste
heat recovery applications and have been subject to significant research over the last two decades. The most common
geometrical design uses a scroll profile generated by the involute of a circle with a constant wall thickness. A major
disadvantage of this approach is that the increase of the geometric expansion ratio is constrained, since it is accompanied
with a large increase in the scroll profile length and is associated with a decreased efficiency. In this paper, the
published literature related to scroll expander geometry is reviewed. Investigations regarding the influence of varying
scroll geometrical parameters on the performance of scroll expanders with a constant wall thickness are first examined.
The use of variable wall thicknesses and their effects on the performance are then considered. Finally, the impact of
scroll expander geometries using unconventional scroll profiles and scroll tip shape variations on the performance is
discussed and summarised. The major conclusion to be drawn from this review is that scroll expanders with variable
wall thickness scrolls should be further designed and developed. It is possible to increase the geometric expansion ratio
without increasing the length of the scroll profiles. CFD simulations are a promising tool to illustrate and understand
the non-uniform and asymmetric inner flow and temperature fields. The related benefits could lead to scroll devices
with variable wall thickness not only improving the performance of organic Rankine cycle (ORC) systems but also
opening a broad new field of applications such as refrigeration cycles and other power cycles where a high pressure
ratio is preferred.
Chew J, Gao F, Palermo D (2018) Flow mechanisms in axial turbine rim sealing, Proc. IMechE part C: Journal of Mechanical Engineering Science SAGE Publications Ltd
This paper presents a review of research on turbine rim sealing with emphasis
placed on the underlying flow physics and modelling capability. Rim seal flows play a
crucial role in controlling engine disc temperatures but represent a loss from the main
engine power cycle and are associated with spoiling losses in the turbine. Elementary
models that rely on empirical validation and are currently used in design do not
account for some of the known flow mechanisms, and prediction of sealing
performance with computational fluid dynamics (CFD) has proved challenging. CFD
and experimental studies have indicated important unsteady flow effects that explain
some of the differences identified in comparing predicted and measure sealing
effectiveness. This review reveals some consistency of investigations across a range
of configurations, with inertial waves in the rotating flow apparently interacting with
other flow mechanisms which include vane, blade and seal flow interactions, disc
pumping and cavity flows, shear layer and other instabilities, and turbulent mixing.
Pitz D, Chew John, Marxen Olaf (2018) Large-eddy simulation of buoyancy-induced flow in a sealed rotating cavity, Journal of Engineering for Gas Turbines and Power 141 pp. 021020-1 ASME
Buoyancy-induced flows occur in the rotating cavities of gas
turbine internal air systems, and are particularly challenging to
model due to the inherently unsteadiness of these flows. While
the global features of such flows are well documented, detailed
analyses of the unsteady structure and turbulent quantities have
not been reported. In this work we use a high-order numerical
method to perform large-eddy simulation (LES) of buoyancyinduced
flow in a sealed rotating cavity with either adiabatic or
heated disks. New insight is given into long-standing questions
regarding the flow characteristics and nature of the boundary
layers. The analyses focus on showing time-averaged quantities,
including temperature and velocity fluctuations, as well as on
the effect of the centrifugal Rayleigh number on the flow structure.
Using velocity and temperature data collected over several
revolutions of the system, the shroud and disk boundary layers
are analysed in detail. The instantaneous flow structure contains
pairs of large, counter-rotating convection rolls, and it is shown
that unsteady laminar Ekman boundary layers near the disks are
driven by the interior flow structure. The shroud thermal boundary
layer scales as approximately Ra?1/3, in agreement with observations for natural convection under gravity.
Kusbeci Mazhar, Chew John (2018) Assessment of wall-modeled LES for pre-swirl cooling systems, ASME Proceedings | Internal Air Systems and Seals (With Turbomachinery) 5B ASME
Although conventional Reynolds-averaged Navier-Stokes
(RANS) models of turbulence are generally used for predicting
the performance of gas turbine pre-swirl systems, these models
are known to have shortcomings. Motivated by the need to
predict mixing where cooled-cooling air (CCA) and un-cooled
cooling air (UCA) streams are introduced in pre-swirl systems,
computational fluid dynamics (CFD) modelling capability is reassessed.
An initial study focuses on a normal jet in crossflow
(JICF), illustrating some of the shortcomings of a popular
Reynolds-averaged Navier-Stokes (RANS) model and the possible
advantages and disadvantages of wall-modeled large eddy
simulation (WMLES). Pre-swirl system studies focus on a previously
investigated low radius feed, direct flow configuration for
which measurements and CFD solutions are available, and extend
this to consider a mixed feed system. The velocities in the
near-jet region of the pre-swirl chamber were predicted differently
by unsteady RANS (URANS) and WMLES, however no significant
differences were observed closer to the receiver holes.
Comparing to measurements shows little overall difference between
the models, with similar results to earlier studies. Although
no measurements are available for a mixed feed system,
comparison of predictions from the two models indicates significant
sensitivity and uncertainty involved in these predictions.
Gao Feng, Poujol N, Chew John, Beard P (2018) Advanced numerical simulation of turbine rim seal flows and consideration for RANS turbulence modelling, Proceedings of ASME Turbo Expo 2018 5B ASME
This paper reports large-eddy simulations (LES) and unsteady
Reynolds-averaged Navier-Stokes (URANS) calculations
of a turbine rim seal configuration previously investigated experimentally.
The configuration does not include any vanes, blades
or external flows, but investigates inherent unsteady flow features
and limitations of CFD modelling identified in engine representative
studies. Compared to RANS and URANS CFD models, a
sector LES model showed closer agreement with mean pressure
measurements. LES models also showed agreement with measured
pressure frequency spectra, but discrepancies were found
between the LES and experiment in the speed and the circumferential
lobe number of the unsteady flow structures. Sensitivity of
predictions to modelling assumptions and differences with experimental
data are investigated through CFD calculations considering
sector size, interaction between the rim cavity and the inner
cavity, outer annulus boundary conditions, and the coolant mass
flow. Significant sensitivity to external flow conditions, which
could contribute to differences with measurements, is shown, although
some discrepancies remain. Further detailed analysis of
the CFD solutions is given illustrating the complex flow physics.
Possible improvement of a steady RANS model using a priori
analysis of LES was investigated, but showed a rather small improvement
in mean pressure prediction.
In this research a spectral element method is used to perform direct numerical simulation (DNS) and implicit large-eddy simulation (LES) of flows induced by centrifugal buoyancy in rotating cavities. These flows occur, for instance, in the compressor cavities of gas turbines internal air systems, in which cooling air is used to extract heat from compressor disks. Buoyancy-induced flows are inherently challenging to study using computational fluid dynamics (CFD), since turbulence models based on the Reynolds-averaged Navier-Stokes (RANS) equations are not able to provide an accurate description of the phenomena induced by the interplay between buoyancy and rotation. For this reason, model-free approaches are desirable, since they can provide an accurate description of the flow physics. First, the method is applied to a rotor/stator configuration, in which regions of laminar, transitional and fully turbulent flow coexist, and the results are compared with experimental data from the literature. Subsequently, flow induced by centrifugal buoyancy in a sealed rotating annulus is investigated using linear stability analysis, DNS and LES. It is shown that the onset of convection for a rotating cavity is similar to that for the problem of Rayleigh-Bénard convection. Analysing flow statistics for different values of the Rayleigh number, it is shown that the disk boundary layer behaves as a laminar Ekman layer, both in terms of its thickness and of its velocity profiles. This is observed even when instantaneous profiles are considered, despite the unsteadiness of the solution. The results also show that the shroud thermal boundary layer scaling is consistent with that of natural convection under gravity. Introducing an axial throughflow of cooling air, some features observed in the sealed cavity are maintained, however a strong reduction in the core temperature and a corresponding increase in the shroud heat transfer occur. The axial throughflow also promotes a significant increase in the range of frequencies observed inside the cavity.
Pitz Diogo B, Chew John, Marxen Olaf (2108) Large-eddy simulation of buoyancy-induced flow in a sealed rotating cavity, Journal of Engineering for Gas Turbines and Power 141 (2) 021020 American Society of Mechanical Engineers
Buoyancy-induced flows occur in the rotating cavities of gas
turbine internal air systems, and are particularly challenging to
model due to the inherently unsteadiness of these flows. While
the global features of such flows are well documented, detailed
analyses of the unsteady structure and turbulent quantities have
not been reported. In this work we use a high-order numerical
method to perform large-eddy simulation (LES) of buoyancyinduced
flow in a sealed rotating cavity with either adiabatic or
heated disks. New insight is given into long-standing questions
regarding the flow characteristics and nature of the boundary
layers. The analyses focus on showing time-averaged quantities,
including temperature and velocity fluctuations, as well as on
the effect of the centrifugal Rayleigh number on the flow structure.
Using velocity and temperature data collected over several
revolutions of the system, the shroud and disk boundary layers
are analysed in detail. The instantaneous flow structure contains
pairs of large, counter-rotating convection rolls, and it is shown
that unsteady laminar Ekman boundary layers near the disks are
driven by the interior flow structure. The shroud thermal boundary
layer scales as approximately Ra?1/3
, in agreement with observations
for natural convection under gravity.
In this thesis, improved and faster CFD based aero-thermo-mechanical methods that can be used to optimize engine configurations early in the design process are described. Axisymmetric models of 3D non-axisymmetric features such as protrusions, holes and honeycomb liners are developed for use in this context, and 3D unsteady CFD is used to investigate the flow physics.

Initially, the research focussed on modelling of a rotor-stator disc cavity. Steady CFD validations for a plane disc and for a disc with protrusion were carried out and a simplified body force model was developed for including the 3D effects of rotating and stationary bolts into the axisymmetric CFD models. The simplified rotor bolt model was verified and validated by comparing the results with Sussex Windage rig test data and 3D CFD data. The simplified stator bolt model was verified using 3D CFD results. The simplified rotor bolt model was found to predict the drag and windage heat transfer with reasonable accuracy compared to 3D sector CFD results. However, 3D sector CFD under-predicts the high core flow swirl and the adiabatic disc surface temperature inboard of the bolt, compared to experimental data.

In the second part of the study, unsteady Reynolds averaged Navier-Stokes (URANS) calculations of the rotating bolts cases were performed in order to better understand the flow physics. Although the rotor-stator cavity with bolts is geometrically steady in the rotating frame of reference, it was found that the rotor bolts generate unsteadiness which creates time-dependent rotating flow features within the cavity. A systematic parametric study is presented giving insight into the influence of the bolt number and the cavity geometric parameters on the time dependent flow within the cavity. The URANS calculations were extended to a high pressure turbine (HPT) rear cavity to show possible unsteady effects due to rotating bolts in an engine case.

Following this, the body force model was adapted to model the rotating hole velocity changes and flow through honeycomb liners. The honeycomb and hole models were verified by comparing the results with available experimental data and 3D CFD calculations.
In the final part of the study, coupled FE-CFD calculations for a preliminary design whole engine thermo-mechanical (WETM) model for a transient square cycle was performed including the effects of non-axisymmetric features. Six cavities around the HPT disc were modelled using CFD. The coupled approach provides more realistic physical convective heat transfer boundary conditions than the traditional approach. The unvalidated baseline thermo-mechanical model results were verified using the high fidelity coupled FE-CFD solution. It was demonstrated that the FE-CFD coupled calculations with axisymmetric modelling of 3D features can be achieved in a few days time scale suitable for preliminary engine design. The simplified CFD based methods described in this thesis could reduce the computational time of transient coupled FE-CFD calculations several orders of magnitude and may provide results as accurate as 2DFE-3DCFD coupled calculations.

Onori Michel, Amirante Dario, Hills Nicholas J., Chew John W. (2019) HEAT TRANSFER PREDICTION FROM LARGE EDDY SIMULATION OF A ROTATING CAVITY WITH RADIAL INFLOW, Proceedings of ASME Turbo Expo 2019: Turbomachinery Technical Conference and Exposition GT 2019 American Society of Mechanical Engineers (ASME)
The paper describes a Large Eddy Simulation (LES) conducted for a non adiabatic rotating cavity with a radial inflow introduced from the shroud. The dimensionless mass flow rate of the radial inflow is Cw = 3500 and the rotational Reynolds number, based on the cavity outer radius, is equal to Req =1:2 x 106. The time averaged local Nusselt number on the heated wall is compared with the experimental data available from the literature, and with those derived from the solution of two Unsteady Reynolds Averaged Navier-Stokes (URANS) eddy viscosity models, namely the Spalart-Allmaras and the k-w SST model. It is shown that the Nusselt number is underpredicted
in the lower part of the disc and over-predicted in the outer region by both URANS models, whereas the LES provides a much better agreement with the measurements. The behaviour results primarily from a different flow structure in the source region, which, in the LES, is found to be considerably more extended and show localized buoyancy phenomena that the URANS models investigated do not capture.
Liu Yuxin, Chew John W., Pekris Michael J., Kong Xiaozhi (2019) The Effect of Inlet Swirl on Brush Seal Bristle Deflections and Stability, Proceedings of ASME Turbo Expo 2019: Turbomachinery Technical Conference and Exposition (GT2019) American Society of Mechanical Engineers (ASME)
This paper considers 3D CFD and structural modelling of brush seals, and investigates the effects of inlet swirl on the bristle pack. The model couples aerodynamic forces generated by CFD to a structural model that includes interaction between bristles. At a critical value of inlet swirl, aerodynamic forces cause circumferential slip of the upstream bristle row. In practice this may lead to instability of the
bristle pack and is consistent with anecdotal reports of seal behavior. The critical swirl velocity was reduced when the downstream pressure level was raised, keeping the same upstream total to downstream static pressure difference. This is caused by the increased dynamic head associated with the inlet swirl. Inclusion of a front plate in the seal design does not offer the intended protection to the bristle pack in highly
swirling environments. This is associated with highly swirling flow impinging on the bristle tips. Fitting of roughness elements on the upstream face of the front plate could improve stability by reducing swirl of the flow impacting on the bristles. Increasing the bristle diameter and bristle
stiffness does not necessarily prevent slip at higher inlet swirl velocities, but reduces the magnitude of slip of the upstream bristles.
Chew John W, Hills Nicholas J (2007) Computational fluid dynamics for turbomachinery internal air systems, Philosophical Transactions A: Mathematical, Physical and Engineering Sciences 365 (1859) pp. 2587-2611 Royal Society
Considerable progress in development and application of computational fluid dynamics (CFD) for aeroengine internal flow systems has been made in recent years. CFD is regularly used in industry for assessment of air systems, and the performance of CFD for basic axisymmetric rotor/rotor and stator/rotor disc cavities with radial throughflow is largely understood and documented. Incorporation of three-dimensional geometrical features and calculation of unsteady flows are becoming commonplace. Automation of CFD, coupling with thermal models of the solid components, and extension of CFD models to include both air system and main gas path flows are current areas of development. CFD is also being used as a research tool to investigate a number of flow phenomena that are not yet fully understood. These include buoyancy-affected flows in rotating cavities, rim seal flows and mixed air/oil flows. Large eddy simulation has shown considerable promise for the buoyancy-driven flows and its use for air system flows is expected to expand in the future.
Palermo Donato M., Gao Feng, Chew John W., Beard Paul F. (2019) EFFECT OF ANNULUS FLOW CONDITIONS ON TURBINE RIM SEAL INGESTION, Proceedings of ASME Turbo Expo 2019: Turbomachinery Technical Conference and Exposition GT 2019 American Society of Mechanical Engineers (ASME)
A systematic study of sealing performance for a chute style turbine rim seal using URANS methods is reported. This extends previous studies from a configuration without external flow in the main annulus to cases with a circumferentially uniform axial flow and vane generated swirling annulus flow (but without rotor blades). The study includes variation of the mean seal-to-rotor velocity ratio, main annulus-to-rotor velocity ratio, and seal clearance. The effects on the unsteady flow structures and the degree of main annulus flow ingestion into the rim seal cavity are examined. Sealing effectiveness is quantified by modeling a passive scalar, and the timescales for the convergence of this solution are considered. It has been found that intrinsic flow unsteadiness occurs in most cases, with the presence of vanes and external flow modifying, the associated flow structures and frequencies. Some sensitivities to the annulus flow conditions are identified. The circumferential pressure asymmetry generated by the vanes has a clear influence on the flow structure but does not lead to higher ingestion rates than the other conditions studied.