Feng Gao

Dr Feng Gao


Research Fellow
PhD
+44 (0)1483 682333
05A AB 01

Academic and research departments

Department of Mechanical Engineering Sciences.

Biography

My qualifications

2014
PhD in mechanical engineering
École Centrale de Lyon
2008
BEng in civil aviation engineering
Beihang University

My publications

Publications

Beard PF, Chew John, Gao Feng, Chana KS (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.
Ma W, Ottavy X, Lu L, Leboeuf F, Gao F (2011) Experimental Study of Corner Stall in a Linear Compressor Cascade, Chinese Journal of Aeronautics
Gao F, Zambonini G, Boudet J, Ottavy X, Lu L, Shao L (2015) Unsteady behavior of corner separation in a compressor cascade: Large eddy simulation and experimental study, Proceedings of the Institution of Mechanical Engineers Part A Journal of Power and Energy
Gao F, Ma W, Boudet J, Ottavy X, Lu L, Leboeuf F (2013) Numerical Analysis of Three-Dimensional Corner Separation in a Linear Compressor Cascade,
Gao F, Ma W, Zambonini G, Boudet J, Ottavy X, Lu L, Shao L (2015) Large-eddy simulation of 3-D corner separation in a linear compressor cascade, Physics of Fluids
Gao F (2014) Advanced numerical simulation of corner separation in a linear compressor cascade,
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.
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.
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.
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.
Gao Feng, Wei Ma, Jinjing Sun, Boudet Jerome, Ottavy Xavier, Yangwei Liu, Lipeng Lu, Liang Shao (2016) Parameter study on numerical simulation of corner
separation in LMFA-NACA65 linear compressor
cascade,
Chinese Journal of Aeronautics 30 (1) pp. 15-30 Elsevier
Large-eddy simulation (LES) is compared with experiment and Reynolds-averaged Navier-Stokes (RANS), and LES is shown to be superior to RANS in reproducing corner separation in the LMFA-NACA65 linear compressor cascade, in terms of surface limiting streamlines, blade pressure coefficient, total pressure losses and blade suction side boundary layer profiles. However, LES is too expensive to conduct an influencing parameter study of the corner separation. RANS approach, despite over-predicting the corner separation, gives reasonable descriptions of the corner separated flow, and is thus selected to conduct a parametric study in this paper. Two kinds of influencing parameters on corner separation, numerical and physical parameters, are analyzed and discussed: second order spatial scheme is necessary for a RANS simulation; incidence angle and inflow boundary layer thickness are found to show the most significant influences on the corner separation among the parameters studied; unsteady RANS with the imposed inflow unsteadiness (inflow angle varying sinusoidally with fluctuating amplitude of 0.92°) does not show any non-linear effect on the corner separation.
Fang Le, Gao Feng (2017) A closure model on velocity structure functions in homogeneous isotropic turbulence., Applied Mathematics and Mechanics 38 (11) pp. 1627-1634 Springer Verlag
Closure models started from Chou?s work have been developed for more than 70 years, aiming at providing analytical tools to describe turbulent flows in the spectral space. In this study, a preliminary attempt is presented to introduce a closure model in the physical space, using the velocity structure functions as key parameters. The present closure model appears to qualitatively reproduce the asymptotic scaling behaviors at small and large scales, despite some inappropriate behaviors such as oscillations. Therefore, further improvements of the present model are expected to provide appropriate descriptions of turbulent flows in the physical space.
Xie Baolin, Gao Feng, Boudet Jerome, Shao Liang, Lu Lipeng (2018) Improved vortex method for large-eddy simulation inflow generation, Computers and Fluids 168 pp. 87-100 Elsevier
The generation of turbulent inflow conditions in large-eddy simulation (LES) is a key ingredient for general applications of LES in both academic turbulent flows and industrial designs with complicated engineering flows. This is because accurate predictions of the fluid behaviour are strongly dependent on the inflow conditions, particularly in turbulent flows at high turbulent Reynolds numbers. This paper aims at improving the vortex method (VM) of Sergent that demands long adaptive distances (12 times the half channel height, for a channel flow at ReÄ = 395) to achieve high quality turbulence, and evaluating the equilibrium of the flow field obtained in terms of both the equilibrium of the mean flow and that of the turbulence (inter-scale turbulent energy transfer). The mean flow equilibrium is checked with classic criteria such as the friction velocity. In order to assess the equilibrium of turbulence, we propose using the velocity-derivative skewness, because it associates with the balance of energy transfer between large- and small-scale fluid motions. Numerical tests with the optimised set of model parameters reveal that the IVM is very efficient, in terms of adaptive distance, in generating high-quality synthetic turbulent fluctuations over a moderate distance: 6h for channel flow and 21´ for flat-plate boundary layer, with h and ´ being respectively the half channel height and the nominal boundary layer thickness.
Fang J., Gao F., Moulinec C., Emerson D.R. (2019) An improved parallel compact scheme for domain?decoupled simulation of turbulence, International Journal for Numerical Methods in Fluids 90 (10) pp. 479-500 Wiley
An improved domain?decoupled compact scheme for first and second spatial derivatives is proposed for domain?decomposition?based parallel computational fluid dynamics. The method improves the accuracy of previously developed decoupled schemes and preserves the accuracy and bandwidth properties of fully coupled compact schemes, even for a very large degree of parallelism, and enables the Navier?Stokes equations to be solved independently on each processor. The scheme is analysed using Fourier analysis and error analysis, and tested on one?dimensional wave?packet propagation, a two?dimensional vortex convection problem, and in the direct numerical simulation of the three?dimensional Taylor?Green vortex problem and turbulent channel flow. Our results demonstrate the scheme's effectiveness in performing direct numerical simulation of turbulence in terms of accuracy and scalability.
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.
Gao Feng, Chew John W., Pitz Diogo B. (2019) Numerical Study of Buoyancy-Driven Flow in a Closed Rotating Annulus, Proceedings of Global Power and Propulsion Society 2019 (GPPS 19) pp. 1-7 Global Power and Propulsion Society
This paper presents a numerical investigation of buoyancy-driven flow in a closed rapidly rotating disc cavity. Pseudo two-dimensional models are considered, with periodic boundary conditions on a thin axial domain. An incompressible model, in which density variation is considered with the Boussinesq approximation, is evaluated through comparisons with a full compressible model. Effects of property (viscosity) variation and dependency on buoyancy parameter (ß?T) and rotational Reynolds number
for a given Rayleigh number, are investigated with the full
compressible model. The mean centrifugal and radial
Coriolis forces are analysed. Heat transfer predictions from
the Boussinesq and compressible models agree to within
10%, for ß?T d 0.2.
Gao Feng, Pitz Diogo B., Chew John W. (2019) Numerical investigation of buoyancy-induced flow in a sealed rapidly rotating disc cavity, International Journal of Heat and Mass Transfer Elsevier
This paper presents buoyancy-induced flow for a sealed rotating cavity with rotational
Rayleigh number Ra in the range 10w to 10y. DNS for an incompressible model with
the Boussinesq approximation is compared with LES for a compressible gas flow model.
The compressible solver's solutions show the shroud Nusselt number scales with Ra0.286,
in close agreement with the corrected experimental correlation and the Ra2/7 scaling for
gravitational heat convection between horizontal plates, but differs from the N u ? Ra1/3
scaling given by the incompressible solver. The shroud thermal boundary layer thickness,
based on the root mean square of the temperature
fluctuation, can be estimated with
»* = 0:5N u-1 Velocities scale approximately with
&a?²?T. Disc laminar Ekman layer
behaviour is confirmed up to Ra = 109. An Ekman layer scrubbing effect, associated with
the viscous energy dissipation, is considered to be mainly responsible for the difference in
N u between the two solvers at Ra = 109, in spite of rather small Eckert number. The
analysis of the turbulent kinetic energy budget shows a dominant constant buoyancy production in the core. The use of the incompressible formulation for the considered problem
is restricted by the applicable range of the Boussinesq approximation characterised by
the buoyancy parameter ²?T and neglect of viscous heating and compressibility effects
characterised by the Eckert number Ec =
&2r2m
=(Cp?T)
.
Gao Feng, Chew John, Marxen Olaf (2020) Inertial waves in turbine rim seal flows, Physical Review Fluids American Physical Society
Rotating fluids are well-known to be susceptible to waves. This has received much attention from
the geophysics, oceanographic and atmospheric research communities. Inertial waves, which are
driven by restoring forces, for example the Coriolis force, have been detected in the research fields
mentioned above. This paper investigates inertial waves in turbine rim seal flows in turbomachinery.
These are associated with the large-scale unsteady
ow structures having distinct frequencies, unrelated
to the main annulus blading, identified in many experimental and numerical studies. These
unsteady flow structures have been shown in some cases to reduce sealing effectiveness and are
difficult to predict with conventional steady Reynolds-averaged Navier-Stokes (RANS) approaches.
Improved understanding of the underlying
ow mechanisms and how these could be controlled is
needed to improve the efficiency and stability of gas turbines. This study presents large-eddy simulations
for three rim seal configurations { chute, axial and radial rim seals { representative of
those used in gas turbines. Evidence of inertial waves is shown in the axial and chute seals, with
characteristic wave frequencies limited within the threshold for inertial waves given by classic linear
theory (i.e. jf=frelj 2), and instantaneous
flow fields showing helical characteristics. The radial
seal, which limits the radial
fluid motion with the seal geometry, restricts the Coriolis force and suppresses the inertial wave.
Palermo Donato M., Gao Feng, Amirante Dario, Chew John W., Revert Anna Bru, Beard Paul F. (2020) WALL-MODELLED LARGE EDDY SIMULATIONS OF AXIAL TURBINE RIM SEALING, ASME Turbomachinery Technical Conference & Exposition 2020
This paper presents WMLES simulations of a chute type
turbine rim seal. Configurations with an axisymmetric annulus flow and with nozzle guide vanes fitted (but without rotor blades) are considered. The passive scalar concentration solution and WMLES are validated against available data in the literature for uniform convection and a rotor-stator cavity flow. The WMLES approach is shown to be effective, giving significant improvements over an eddy viscosity turbulence model, in prediction of rim seal effectiveness compared to research rig measurements. WMLES requires considerably less computational time than wall-resolved LES, and has the potential for extension to engine conditions. All WMLES solutions show rotating inertial waves in the chute seal. Good agreement between WMLES and measurements for sealing effectiveness in the configuration without vanes is found. For cases with vanes fitted the WMLES simulation shows less ingestion than the measurements, and possible reasons are discussed.

Additional publications