Dr Michael J Pekris

Multi-point ignition and non-equilibrium plasma ignition technologies were both certified to enhance the ignition and combustion processes of ammonia (NH3). High-frequency Nanosecond Surface dielectric barrier discharge (nSDBD) ignition is a promising strategy to carry out both multi-point ignition and non-equilibrium plasma ignition with high energy supply. However, there is little research on how equivalence ratio, initial pressure, and initial temperature affect NH3/air mixtures ignited by nSDBD in Constant Volume Chamber (CVC). This study experimentally-investigated the plasma assisted NH3/air ignition with a high-frequency nSDBD device in a CVC. The effects of equivalence ratio, initial pressure, and initial temperature on this plasma assisted NH3/air ignition strategy were evaluated by discharge performance, flame morphology, and combustion parameters. Results showed that initial pressure strongly influenced the total supplied energy to nSDBD, with a bell-shaped tendency as the initial pressure increased. Near-stoichiometric mixtures exhibited the fastest flame kernel development, the highest pressure rise, and the greatest heat release. Lower initial pressure and higher initial temperature generally promoted flame kernel growth but delayed pressure rise and heat release, though extremely low pressure prevented ignition. [Display omitted] •Nanosecond-scale high-frequency nSDBD was applied to ignite NH3/air mixtures.•Effects of equivalence ratio, initial pressure, and initial temperature on NH3 ignition.•Near stoichiometric equivalence ratios achieved optimal combustion.•Increasing initial temperature promoted NH3 ignition and combustion.

Brush seals offer a superior sealing effectiveness compared to labyrinth seals. However, widespread use of brush seals is constrained by deleterious behaviors such as pressure-stiffening and hysteresis. For the latter, the bristles bend during the shaft incursion process and do not fully recover during the shaft retraction process. An opening gap is created, which increases seal leakage unless the pressure load drops to a certain level. In the present work, analytical and numerical models based on a single bristle are proposed to capture the seal’s response to shaft displacement with and without pressure loading. The models are validated using static stiffness tests at an unpressurized condition from literature. The main results show that modeling of the backing ring friction is essential to capture the bristle hang-up behavior. Shaft friction dominates at unpressurized conditions, while backing ring friction dominates at high pressure loading. An expression for shaft hang-up displacement has been derived. A sensitivity study shows that seals with shallow lay angle, short bristle length, and large bristle diameter are less prone to hang-up problems. The models developed in the present framework have been shown to qualitatively capture the pressure stiffening, hysteresis, bristle hang-up, and shaft rotation effects.

Brush seals are plausible replacements for conventional labyrinth seals in gas turbines for managing internal air system flows and leakages. They can offer superior leakage performance compared to labyrinth seals due to their compliant nature, and a reduced effective clearance during operation. Despite their improved sealing performance, highly swirling flow and aerodynamic forces on the upstream bristles could lead to aero-elastic instability within the bristle pack. This study investigates grooves as a means of improving brush seal robustness in high-shaft speed locations by reducing the inlet swirl that is incident on the bristle pack. The material removed and implied manufacturing effort and cost are considered. A parametric study of a simple groove geometry was conducted using CFD and a porous medium representation of the bristle pack whose resistance coefficients were calibrated to Bayley and Long’s data to achieve representative seal leakages. This identified groove length, width, angle and pitch as the important groove parameters for swirl reduction and demonstrated that the performance of ribs from previous research can be replicated and improved upon. A Design of Experiments (DOE) approach was adopted to investigate a novel groove design geometry. Combining a horizontal channel with an inclined groove enables a higher pitch to achieve the same swirl reduction by increasing drag and exploiting fluidic effects. The results indicate that the novel groove design performs as intended in substantially reducing the swirl incident on the bristle pack. Adding these features to the traditional front plate may improve brush seal robustness by reducing the effect of aerodynamic forces which could drive bristle pack instabilities, thus having the potential to aid their deployment in high-radius or high-shaft speed engine locations.

CFD-FEA Simulation of Leaf Seal Dynamics * Ramesh Kumar, * Michael J. Pekris, * John W. Chew, * Dario Amirante and * Nicholas J. Hills AIAA 2018-4897 AVS-03: High-Speed Simulation and Drag Reduction Testing • Wednesday, 11 July 2018 • 1600 hrs https://doi.org/10.2514/6.2018-4897

The application of compliant filament seals to jet engine secondary air systems has been shown to yield significant improvements in specific fuel consumption and improved emissions. One such technology, the leaf seal, provides comparable leakage performance to the brush seal but offers higher axial rigidity, significantly reduced radial stiffness and improved compliance with the rotor. Investigations were carried out on the Engine Seal Test Facility at the University of Oxford into the behavior of a leaf seal prototype at high running speeds. The effects of pressure, speed and cover plate geometry on leakage and torque are quantified. Early publications on leaf seals showed that air-riding at the contact intemface might be achieved. Results are presented which appear to confirm that air-riding is taking place. Consideration is given to a possible mechanism for torque reduction at high rotational speeds.

Leaf seals are filament seals for use at static to rotating interfaces in the engine secondary air system. They offer reduced leakage rates and better off-design performance over conventional labyrinth seals. If compared with advanced brush seals, leaf seals are more compliant due to their lower stiffness and can withstand higher axial pressure differences. Although leaf seals can exhibit hydrodynamic air-riding, this is not always the case and seal-rotor contact can occur. As a result, friction between the leaf tips and the rotor causes heat generation and wear. To predict the diameter of the rotating shaft and the seal life, the shaft and seal interface temperature needs to be estimated. In the steady state, this is determined by the ratio of convective heat transfer through the seal to that through the shaft. To that end, the convective heat transfer characteristics of the flow over the shaft around the seal are required to build accurate thermal models. In this paper, the convective heat transfer coefficient (HTC) distribution in the close vicinity of a typical leaf seal is investigated in a new test facility. The experimental setup and test method are described in detail, and accuracy considerations are included. The methodology employed to derive HTC is explained with reference to an analogous computational fluid dynamics (CFD) model. The importance of the choice of an appropriate driving gas temperature is demonstrated. Experimental HTC maps are presented for a blow-down seal geometry operating over a range of engine representative pressure ratios. Insight is gained into the flow field characteristics and heat transfer around the seal.

Leaf seals are filament seals for use at static to rotating interfaces in the engine secondary air system. They offer reduced leakage rates and better off-design performance over conventional labyrinth seals. If compared with advanced brush seals, leaf seals are more compliant due to their lower stiffness and can withstand higher axial pressure differences. Although leaf seals can exhibit hydrodynamic air-riding, this is not always the case and seal-rotor contact can occur. As a result, friction between the leaf tips and the rotor causes heat generation and wear. To predict the diameter of the rotating shaft and the seal life, the shaft and seal interface temperature needs to be estimated. In the steady state this is determined by the ratio of convective heat transfer through the seal to that through the shaft. To that end, the convective heat transfer characteristics of the flow over the shaft around the seal is required to build accurate thermal models. In this paper the convective heat transfer coefficient (htc) distribution in the close vicinity of a typical leaf seal is investigated in a new test facility. The experimental setup and test method are described in detail and accuracy considerations are included. The methodology employed to derive htc is explained with reference to an analogous CFD model. The importance of the choice of an appropriate driving gas temperature is demonstrated. Experimental htc maps are presented for a blow down seal geometry operating over a range of engine representative pressure ratios. Insight is gained into the flow field characteristics and heat transfer around the seal.

Advanced contacting seals, such as leaf seals or brush seals, can offer reduced leakage during engine operation when compared to conventional labyrinth seals. The flexible elements of these seals provide better compliance with the rotor during flight manoeuvres. The functionality and performance retention attributes of an engine-scale prototype leaf seal have been investigated on a seal test facility at Rolls-Royce that achieves engine-representative pressures and speeds and allows dynamic control of the seal position relative to the rotor, both concentric and eccentric. In this paper the experimental setup and the test method are described in detail, including the quantification of the measurement uncertainty developed to ASME standard PTC 19.1. Experimental data are presented that show the variations in leakage and torque over typical variations of the test parameters. Insight is gained into the interactions between the operating pressure and speed and the concentric and eccentric movements imposed on the seal.

Compliant contacting filament seals such as brush seals are well known to give improved leakage performance and hence specific fuel consumption benefit compared to labyrinth seals. The design of the brush seal must be robust across a range of operating pressures, rotor speeds, and radial build-offset tolerances. Importantly the wear characteristics of the seal must be well understood to allow a secondary air system suitable for operation over the entire engine life to be designed. A test rig at the University of Oxford is described which was developed for the testing of brush seals at engine-representative speeds, pressures, and seal housing eccentricities. The test rig allows the leakage, torque, and temperature rise in the rotor to be characterized as functions of the differential pressure(s) across the seal and the speed of rotation. Tests were run on two different geometries of bristle pack with conventional, passive, and active pressure-balanced backing ring configurations. Comparison of the experimental results indicates that the hysteresis inherent in conventional brush seal design could compromise performance (due to increased leakage) or life (due to exacerbated wear) as a result of reduced compliance. The inclusion of active pressure-balanced backing rings in the seal designs are shown to alleviate the problem of bristle-backing ring friction, but this is associated with increased blow-down forces which could result in a significant seal-life penalty. The best performing seal was concluded to be the passive pressure-balanced configuration, which achieves the best compromise between leakage and seal torque. Seals incorporating passive pressure-balanced backing rings are also shown to have improved heat transfer performance in comparison to other designs.

Aero-engine gas turbine performance and efficiency can be improved through the application of compliant shaft seal types to certain sealing locations within the secondary air system. Leaf seals offer better performance than traditional labyrinth seals, giving lower leakage flows at design duties. However, for aero-engine applications, seal designs must be able to cope with relatively large off-design seal closures and closure uncertainties. The two-way coupling between temperatures of seal components and seal closures, through the frictional heat generated at the leaf–rotor interface when in contact, represents an important challenge for leaf seal analysis and design. This coupling can lead to leaf wear and loss, rotor overheating, and possibly to unstable sealing system behavior (thermal runaway). In this paper, we use computational fluid dynamics (CFD), finite element (FE) thermal analysis, and experimental data to characterize the thermal behavior of leaf seals. This sets the basis for a study of the coupled thermomechanical behavior. CFD is used to understand the fluid-mechanics of a leaf pack. The leaf seal tested at the Oxford Osney Laboratory is used for the study. Simulations for four seal axial Reynolds number are conducted; for each value of the Reynolds number, leaf tip-rotor contact, and clearance are considered. Distribution of mass flow within the leaf pack, distribution of heat transfer coefficient (HTC) at the leaf surface, and swirl velocity pick-up across the pack predicted using CFD are discussed. The experimental data obtained from the Oxford rig is used to develop a set of thermal boundary conditions for the leaf pack. An FE thermal model of the rig is devised, informed by the aforementioned CFD study. Four experiments are simulated; thermal boundary conditions are calibrated to match the predicted metal temperatures to those measured on the rig. A sensitivity analysis of the rotor temperature predictions to the heat transfer assumptions is carried out. The calibrated set of thermal boundary conditions is shown to accurately predict the measured rotor temperatures.

The application of compliant filament seals to jet engine secondary air systems has been shown to yield significant improvements in specific fuel consumption and improved emissions. One such technology, the leaf seal, provides comparable leakage performance to the brush seal but offers higher axial rigidity, significantly reduced radial stiffness, and improved compliance with the rotor. Investigations were carried out on the Engine Seal Test Facility at the University of Oxford into the behavior of a leaf seal prototype at high running speeds. The effects of pressure, speed, and cover plate geometry on leakage and torque are quantified. Earlier publications on leaf seals showed that air-riding at the contact interface might be achieved. Results are presented which appear to confirm that air-riding is taking place. Consideration is given to a possible mechanism for torque reduction at high rotational speeds.

Aero-engine gas turbine performance and efficiency can be improved through the application of compliant shaft seal types to certain sealing locations within the secondary air system. Leaf seals offer better performance than traditional labyrinth seals, giving lower leakage flows at design duties. However, for aero-engine applications, seal designs must be able to cope with relatively large off-design seal closures and closure uncertainties. The two-way coupling between temperatures of seal components and seal closures, through the frictional heat generated at the leaf-rotor interface when in contact, represents an important challenge for leaf seal analysis and design. This coupling can lead to leaf wear and loss, rotor overheating, and possibly to unstable sealing system behaviour (thermal runaway). In this paper we use CFD, FE thermal analysis, and experimental data to characterise the thermal behaviour of leaf seals. This sets the basis for a study of the coupled thermo-mechanical behaviour. CFD is used to understand the fluid-mechanics of a leaf pack. The leaf seal tested at the Oxford Osney Laboratory is used for the study. Simulations for four seal axial Reynolds number are conducted; for each value of the Reynolds number, leaf tip-rotor contact and clearance are considered. Distribution of mass flow within the leaf pack, distribution of heat transfer coefficient at the leaf surface, and swirl velocity pick-up across the pack predicted using CFD are discussed. The experimental data obtained from the Oxford rig is used to develop a set of thermal boundary conditions for the leaf pack. An FE thermal model of the rig is devised, informed by the aforementioned CFD study. Four experiments are simulated; thermal boundary conditions are calibrated to match predicted metal temperatures to those measured on the rig. A sensitivity analysis of the rotor temperature predictions to the heat transfer assumptions is carried out. The calibrated set of thermal boundary conditions is shown to accurately predict the measured rotor temperatures.

In an effort to reduce gas turbine specific fuel consumption and to increase specific thrust, advanced sealing technologies have been deployed for the purpose of secondary air flow management. One such technology, the brush seal, provides a more compliant seal and hence improved leakage performance over the legacy industry standard, the labyrinth seal. It is known that brush seal geometry has a strong effect on the loading, deformations, temperatures and flows in the bristle pack. There is limited understanding of the complex interactions between the geometric variables. This paper describes a methodology for the modelling of an idealised brush seal domain based on Computational Fluid Dynamics. Bristle pressure and force distributions, temperature distributions and tip contact forces are presented. This methodology is used to examine the sensitivity of these parameters to the geometric input variables for a contacting seal configuration, using a Design of Experiments approach. Inferences are drawn from the results to determine which of the geometric parameters are most influential in brush seal pack flow-induced behaviour, and the strength of the coupling between these parameters and the key performance indicators.

Advanced contacting seals, such as leaf seals or brush seals, can offer reduced leakage during engine operation when compared to conventional labyrinth seals. The flexible elements of these seals provide better compliance with the rotor during flight maneuvers. The functionality and performance retention attributes of an engine-scale prototype leaf seal have been investigated on a seal test facility at Rolls-Royce that achieves engine-representative pressures and speeds and allows dynamic control of the seal position relative to the rotor, both concentric and eccentric. In this paper, the experimental setup and the test method are described in detail, including the quantification of the measurement uncertainty developed to ASME standard PTC 19.1. Experimental data are presented that show the variations in leakage and torque over typical variations of the test parameters. Insight is gained into the interactions between the operating pressure and speed and the concentric and eccentric movements imposed on the seal.

Compliant contacting filament seals such as brush seals are well known to give improved leakage performance and hence specific fuel consumption benefit compared to labyrinth seals. The design of the brush seal must be robust across a range of operating pressures, rotor speeds and radial build-offset tolerances. Importantly the wear characteristics of the seal must be well understood to allow a secondary air system suitable for operation over the entire engine life to be designed. A test rig at the University of Oxford is described which was developed for the testing of brush seals at engine-representative speeds, pressures and seal housing eccentricities. The test rig allows the leakage, torque and temperature rise in the rotor to be characterized as functions of the differential pressure(s) across the seal and the speed of rotation. Tests were run on two different geometries of bristle-pack with conventional, passive and active pressure-balanced backing ring configurations. Comparison of the experimental results indicates that the hysteresis inherent in conventional brush seal design could compromise performance (due to increased leakage) or life (due to exacerbated wear) as a result of reduced compliance. The inclusion of active pressure-balanced backing rings in the seal designs are shown to alleviate the problem of bristle-backing ring friction, but this is associated with increased blow-down forces which could result in a significant seal-life penalty. The best performing seal was concluded to be the passive pressure-balanced configuration, which achieves the best compromise between leakage and seal torque. Seals incorporating passive pressure-balanced backing rings are also shown to have improved heat transfer performance in comparison to other designs.

Brush seals can be used in the secondary air systems of gas and steam turbines to reduce parasitic leakages and engine specific fuel consumption. Application of these seal types in highly pressurised and highly swirling environments is limited due to the inherent risk of aerodynamic instability and seal failure. This paper considers coupled 3D CFD and structural modelling of brush seals, and applies the technique to investigate the effects of inlet swirl on the bristle pack. The model applies aerodynamic forces generated by CFD to a bristle pack model that includes interaction between bristles. Iteration between CFD and structural models is used to ensure consistency between the fluid and structural solutions. Inlet swirl is shown to increase bristle circumferential aerodynamic forces. At a critical value of inlet swirl, the aerodynamic force on the upstream bristles is sufficient to cause circumferential slip of the upstream bristle row, despite axial compression of the bristle pack under its operating differential pressure. 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, and in fact further lowers the critical swirl velocity where bristle slip occurs. This is associated with highly swirling flow impinging on the bristle tips. 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.

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.

As conventional aircraft designs approach their limits in terms of efficiency and emissions, a drastic change to the architecture of conventional platforms is required if the environmental targets of the next several decades are to be met. Boundary Layer Ingestion is one of industry’s most promising answers to the challenges of the future, identifying a potential step-change in performance in more integrated propulsion and airframe systems. This paper investigates the behaviour of a boundary layer ingesting solution of a closely embedded wing-electric ducted fan design, with focus on the implications of the aerodynamic coupling on the individual performance of both the aerodynamic and propulsive elements as well as on the assessment of the reliability of a low order panel code method. Wind tunnel testing was undertaken to understand the flow physics at different combinations of airframe and propulsor operating conditions; in addition, part of the data used for the experimental validation of a panel method model for predicting the upstream inlet flow conditions. It was found that there were clear local and extended upstream effects of the propulsor on the performance of the aerodynamic surface, resulting from the different combinations of suction strength and nacelle blockage. Similar trends were observed in the numerical code predictions, and identified limitations of the methodology in defining the experimental boundary conditions of the propulsor to be imposed in CFD. The study of the response of the propulsor to varying inlet boundary conditions, created by varying wing angles of attack was also carried out, however, small changes in flow velocity combined with measurement errors of the current system, prevented any solid conclusions being drawn about the impact of distorted inlet flow on propulsor performance.

Transcritical carbon dioxide waste heat recovery systems and the construction of scroll expanders have recently been hot topics. The flank clearance, located between the orbiting and fixed scroll, has a vital impact on the scroll expander performance. This paper estimates the effect of the flank clearance on the expander’s thermodynamic performance (first-law efficiency) based on computational fluid dynamics (CFD) simulations. The manufacturing cost of different flank clearances is also considered to enhance the feasibility of the machinery design. The computational cost for different flank clearance cases is significantly reduced with a surrogate-assisted multi-objective optimisation algorithm (SAMOA), which also supports modelling the trade-off relationship between manufacturing cost and machinery efficiency. The results indicated that an increasing flank clearance negatively affects the first-law thermal efficiency. The efficiency decreased from 87.41% to 44.83% moving from 20 to 200 μm flank clearances. The SAMOA successfully reduced the computational cost of the dynamic mesh CFD model from 90 h to 15 s with 0.6% discrepancy. The final Pareto solutions presented a clear trade-off relationship between the first-law efficiency and manufacturing cost and promised a diversity of optimum solutions. The “knee points” for the relationship were 25, 55, and 127 μm, which provided flexible clearance choices based on the importance of either machinery efficiency or manufacturing cost.

Recent developments in the field of renewable energy have led to a renewed interest in low-grade heat (< 500 K). The low-grade heat is widely wasted by the lack of efficient heat recovery technologies. It is also limited by the system size, which defines as the micro to small-scale (< 50 kW). Although ORC based unit has been implemented in this field, the CO2 based waste heat recovery units can be more capable in the size construction. The performance of the expander plays a vital role in the system's efficiency. Thus, the current paper provides thermodynamic and CFD analysis of a scroll expander regarding a micro-scale T-CO2 recovery system (< 10 kW) with a 400 K low-grade heat source. In the current CFD model, all the fluid domains were constructed by structural mesh. It also successfully integrated with the thermodynamic table to simulate two-phase T-CO2. This model can be the first scroll expander model for T-CO2 power system and gap the bridge of utilising the scroll machinery in this field. The CFD methodology was successfully validated by the new-built testing platform and previous data. The energy performance of T-CO2 and ORC (R123) based scroll expanders are compared by isentropic and exergy efficiency. The results showed that isentropic and exergy efficiencies of T-CO2 were 7% and 14% higher than the R123. It also identified higher irreversibilities of T-CO2 by the exergy of the working fluids. The pressure and temperature distributions identified the over-expansion and reversed flow characteristics, and the pressure imbalance of the initial expansion chambers denoted the reversed flow.

The secondary air system of a modern gas or steam turbine is configured to satisfy a number of requirements, such as to purge cavities and maintain a sufficient flow of cooling air to key engine components, for a minimum penalty on engine cycle efficiency and specific fuel consumption. Advanced sealing technologies, such as brush seals and leaf seals, are designed to maintain pressures in cavities adjacent to rotating shafts. They offer significant reductions in secondary air parasitic leakage flows over the legacy sealing technology, the labyrinth seal. The leaf seal comprises a series of stacked sheet elements which are inclined relative to the radial direction, offering increased axial rigidity, reduced radial stiffness, and good leakage performance. Investigations into leaf seal mechanical and flow performance have been conducted by previous researchers. However, limited understanding of the thermal behavior of contacting leaf seals under sustained shaft contact has led to the development of an analytical model in this study, which can be used to predict the power split between the leaf and rotor from predicted temperature rises during operation. This enables the effects of seal and rotor thermal growth and, therefore, implications on seal endurance and rotor mechanical integrity to be quantified. Consideration is given to the heat transfer coefficient in the leaf pack. A dimensional analysis of the leaf seal problem using the method of extended dimensions is presented, yielding the expected form of the relationship between seal frictional power generation, leakage mass flow rate, and rotor temperature rise. An analytical model is derived which is in agreement. Using the derived leaf temperature distribution formula, the theoretical leaf tip temperature rise and temperature distributions are computed over a range of mass flow rates and frictional heat values. Experimental data were collected in high-speed tests of a leaf seal prototype using the Engine Seal Test Facility at Oxford University. These data were used to populate the analytical model and collapsed well to confirm the expected linear relationship. In this form, the thermal characteristic can be used with predictions of mass flow rate and frictional power generated to estimate the leaf tip and rotor temperature rise in engine operation.

In recent decades, the carbon dioxide cycles, including supercritical carbon dioxide cycle, transcritical carbon dioxide Rankine cycle and refrigeration cycle, have been proven effective due to the high efficiency and compact structure, and received increasing interests. The performance of the expander in the power cycles, particularly in micro-scale applications, is one of the essential components that determine the cycle performance and still remains a significant challenge. This paper presents a critical overview of micro-scale (

When subject to highly swirling inlet flow, the bristles on the upstream face of a brush seal in gas turbine engines tend to slip circumferentially, which may lead to aeromechanical instability and seal failure. In this article, a new design of the front plate of brush seal, which mitigates this effect, is presented. Angled ribs on the upstream side of the front plate are used to reduce the swirl of the flow impacting on the bristle pack. The effects of the rib geometry, including angle of inclination and height-to-spacing ratio, are investigated using computational fluid dynamics, and a bulk porous medium model of the bristle pack, on a simple seal geometry. Results show that the ribs can effectively regulate the flow upstream of the bristle pack, reducing the swirl and channeling flow radially inward to the sealing section, resulting in decreased circumferential forces on the bristles. Ribs inclined at 20° to the radial direction and with height-to-spacing ratio of 0.4 were selected as the most effective of those investigated for the seal geometry under study. A model of an aeroengine preswirled cooling air chamber was created to give insight into the inlet swirl boundary conditions that a preswirl seal brush seal could be subjected to at a range of leakage flow rates and inlet swirl velocities. The new design and upstream roughness feature substantially reduced inlet swirl velocity incident on the bristle pack. The findings in this work could have a significant impact on brush seal design and, in particular, mitigate a significant operational risk of swirl-induced instability in high-pressure, high-speed shaft seal locations.