Bleed Mass Flow Rate Research Articles

Experimental and numerical investigation of the effects of porous bleed systems on a model scramjet inlet under high backpressure conditions

In this study, we conducted experimental and numerical investigations to assess the effects of backpressure and configurations of porous bleeds on a scramjet inlet's performance at Mach 5. Experiments in a high-enthalpy wind tunnel, using a backpressure controller and a porous bleed with 1 mm holes and 10 mm lateral spacing, were paired with Reynolds-averaged Navier-Stokes simulations to explore the mitigation of flow separation and the prevention of inlet unstart under various backpressure conditions. The simulations provided insights into how backpressure levels and porous bleed geometries impact internal flow structures, as well as the critical backpressure ratio at which inlet unstart occurs. Additional simulations varied the bleed system's hole diameter and spacing, identifying configurations that optimize aerodynamic performance by enhancing total pressure recovery and Mach number at the isolator exit, while reducing bleed mass flow rates. The study also quantified the impact of these configurations on engine thrust, determining that certain bleed system designs significantly improve thrust by efficiently suppressing the interaction between the core flow and corner recirculation zones. This study examined the internal three-dimensional flow structure characteristics under high back pressure and provided insights into porous bleed configuration capable of efficiently suppressing inlet unstart.

Novel Simplified Numerical Simulation Method for Modeling Bleed Holes in Supersonic Inlets

A novel simplified numerical simulation method for bleed holes in supersonic inlets was developed to estimate the bleed mass flow rate and simulate the flowfield structure in the bleed region. First, the Prandtl–Meyer expansion theory was employed to calculate the location of the barrier shock and reconstruct the flow structure inside the bleed hole. Next, a novel discrimination algorithm was developed to distinguish the grids connected to the bleed hole in the bleed zone instead of directly modeling the hole opening and plenum chamber. Finally, the bleed mass flow rate was obtained based on the boundary-layer properties in the bleed region and the fitting scaled coefficients. This method was also evaluated by performing numerical simulations for a series of different bleeding situations. For all the examined cases, the simulation results were in good agreement with the experimental data, and the number of grid points’ requirement for modeling the bleed hole as compared with the fully resolved method was considerably reduced. Moreover, the proposed method was successfully applied to simulate porous bleed systems in a mixed-compression supersonic inlet. This illustrates that the proposed method is expected to be a useful engineering tool for designing the bleed system of the supersonic inlets.

Experimental investigation of hole-type bleed for active flow control in an axial compressor cascade with tip clearance

Boundary layer aspiration using bleeding is a potential technique for active flow control. This study explores the influence mechanism of hole-type bleed on the secondary flow loss through a low-speed wind tunnel experiment. Compared with the suction slot, the hole-type bleed for boundary layer aspiration has the advantages of good flexibility and high strength. In this study, the tip leakage vortex (TLV) and passage vortex (PV) in a compressor cascade with a tip clearance are effectively controlled through the hole-type bleed experimentally. The optimal bleeding hole position is located at 25% cx downstream of the blade leading edge near the blade suction surface. An 8.34% performance benefit in the Cpt with a bleed mass flow rate of 0.66% is obtained. It is found that the optimal bleeding hole position is highly correlated to the position where the TLV and PV originate in the baseline. Moreover, the balance between the controlling of the TLV and PV is considered to strongly determine the performance benefit obtained in the compressor cascade. The findings reveal that the secondary flow loss control mechanism under the hole-type bleed from two aspects: delayed vortex origination and clearance blockage.

Effects of bleed type on the performance of a supersonic intake

An extensive experimental investigation was conducted to reveal the effects of the porous and slot bleeds on the performance and flow control in a supersonic intake. The experiments were conducted on a supersonic intake at the design freestream Mach number of 2.0 and extended to the off-design Mach numbers of 1.8 and 2.2, all at the angle of attack of zero degrees. For every freestream Mach number, eight back pressures were examined, where a total of twenty-four cases were studied. It was found that the slot bleed may degrade the total pressure recovery of the intake, while employing the porous bleed leads to the enhancement of the total pressure recovery. Moreover, the bleed mass flow rate is smaller for the porous bleed and it leads to the lower flow distortion as compared with the slot bleed. However, the slot bleed is more powerful in postponing the buzz onset.

Effects of bleed hole size on supersonic boundary layer bleed mass flow rate

The bleed hole diameter, depth, and boundary layer thickness are key design parameters of a supersonic bleed system. The evolution trend of single-hole bleed flow coefficient with the ratio of boundary layer thickness to bleed hole diameter and the ratio of bleed hole depth to diameter is investigated by numerical simulations under choking and non-choking conditions. The results show that the subsonic leading edge of the circular hole and the subsonic part of the boundary layer are the main factors causing lateral flow of the bleed hole. The effect of diameter on bleed mass flow rate is due to the viscous effect which reduces the effective diameter. The larger the ratio of displacement thickness to bleed hole diameter, the more obvious the viscous effect is. The depth affects bleed flow rate by changing the opening and closing states of the separation zone. When a certain depth is reached, the development of the boundary layer reduces the effective captured stream tube and thus reduces the bleed mass flow rate. The main objective of the study is to obtain the physical mechanism of the bleed hole size parameters affecting the bleed mass flow rate, and to provide theoretical guidance for the selection of the size of bleed holes in the design of a porous arrays bleed system in hypersonic inlets.

Numerical Studies on Chemical Non-Equilibrium Flow of the Base-Bleed Unit Wake

ABSTRACTNumerical studies of compressible base flows with base bleed injection as an effective way to control the base flow for the base drag reduction and heat energy addition of axisymmetric projectiles with a boattailed afterbody in supersonic freestream are carried out by considering the base burning process. The idea developed in the study is to obtain the lowest base drag by analyzing the complex fluid dynamic characteristics found in a supersonic base flow field, including combined effects of boattailing and secondary combustion of the wake under different conditions. Overall fluid dynamic and chemical non-equilibrium flow are then simulated by incorporating the H2-CO combustion model with 12 reaction steps involving eight reactive species (H, H2, H2O, OH, CO, CO2, O, and O2) into a Navier–Stokes computer code. Various base flow and component distribution characteristics are obtained by changing injection parameter I, which is defined as the bleed mass flow rate normalized by the product of the base area and the freestream mass flux, and the bleed temperature. The results obtained through the present study show that, with increasing injection parameter I, the average base pressure is found to increase quickly initially, attain a slow increase near an injection parameter of I = 0.007, and then remain constant with further increase in I. Moreover, based on changing the bleed temperature, the base pressure rises and the heat energy addition as well as mass addition mechanisms associated with base secondary combustion are found to be higher than that without base secondary combustion. The secondary combustion results in a significant increase in flame temperature and changes the product composition, which cannot be ignored, although the chemical kinetics and fluid dynamic will fulfill another important role. Thus, a better effect on base drag reduction as well as base pressure increase can be attained by adopting appropriate injection parameter and bleed temperature.

다공도 및 팽창파의 영향을 고려한 BLEED 경계조건 수치 모델링의 정확도 향상 연구

The present paper deals with accuracy improvement of a bleed boundary condition model used to improve the performance of supersonic inlets. In order to accurately predict the amount of bleed mass flow rates, this study performs a scaling of sonic flow coefficient data for 90-degree bleed holes in consideration of Prandtl-Meyer expansion theory. Furthermore, it is assumed that porosity varies with stream-wise location of the porous bleed plate to accurately predict downstream boundary layer profiles. The bleed boundary condition model is demonstrated through Computational Fluid Dynamics(CFD) simulations of bleed flows on a flat plate with/without an oblique shock. As a result, the bleed model shows the improved accuracy of bleed mass rates and downstream boundary layer profiles.

Aerodynamic design of a highly loaded supersonic aspirated axial flow compressor stage

A non-standard aerodynamic design idea has been proposed for the supersonic or the transonic axial flow compressors. The aim of this non-standard design idea is to further increase the stage load efficiently with boundary layer suction used only in the stator, which can reduce the design difficulty of the air bleed system in the rotating part and improve the reliability of the stage. Compared with the conventional supersonic shock-in-type rotor, the rotor designed by this method can further increase the turning of the flow to enhance the stage work. Compared with the traditional supersonic impulse rotor, it can lower the rotor exit absolute Mach number to relieve the design difficulty of the downstream stator. But by increasing the turning of the flow in the rotor, the stator entrance Mach number will be increased inevitably, so boundary layer suction is used to solve its internal flow problems. Based on the numerical simulation, a verification stage has been designed to demonstrate the feasibility of this non-standard aerodynamic idea. From the three-dimensional viscous numerical results, a stage with total pressure ratio 2.56 has been attained at tip tangential speed 370 m/s. For this aspirated stage, three kinds of efficiency evaluation methods are applied, and the corresponding stage maximum efficiency is around 91% (calculated by formula (5)), 87% (calculated by formula (6)), and 83.4% (calculated by formula (7)) separately. The total bleed mass flow rate in the stator is around 5.8% of the inlet.

Theoretical analysis of effects of boundary layer bleed on scramjet thrust

The effects of boundary layer bleed on the scramjet thrust are studied in the present paper. A theoretical model is developed to evaluate the thrust increment and influencing factors. The thrust increment resulting from the bleed is dominated by the rise in total pressure recovery and bleed mass flow rate. The bleed mass flow rate exerts stronger impact on the engine thrust than the total pressure. According to current bleed design, it is a severe challenge for the engine to enhance its total pressure to maintain the original thrust when there is no bleeding. Furthermore, the initial total pressure recovery, fuel mass addition, combustion efficiency and area ratio of engine exit to entrance can affect the contributions of the bleeding to the thrust increment. The scramjet needs a higher rise in total pressure recovery to counteract the negative effect of bleed mass loss at higher initial total pressure recovery or larger area ratio of engine exit/entrance. More heat release results in a little lower demand on the rise in total pressure recovery for maintaining the scramjet thrust. These results will aid in understanding the fundamental mechanism of bleeding on engine thrust.

Numerical and Experimental Investigations of a Compressor Cascade Flow With Secondary Air Removal

The paper presents numerical and experimental results for a low speed compressor cascade with bleed air removal at the endwall. The aerofoil design is representative for a stator blade in a modern high pressure compressor near the casing wall. Secondary air is commonly supplied by simple bleed geometries downstream of stator rows. The focus of the present investigation was the systematic development of a passage integrated bleed configuration. With the assumption of an invariable bleed mass flow rate it should be designed to provide an advantageous effect on the main flow. Furthermore, a high pressure recovery in the bleed flow was aspired. Steady 3D RANS simulations were performed using the Spalart-Allmaras turbulence model. In both numerical simulations and experiments, an improved performance was found. Beside reduced losses and increased pressure rise, the wake flow downstream of the customized bleed geometry was found to be more homogeneous with decreased deviations due to a favorable influence on the secondary flow.

Numerical Study of Aerodynamic Losses of Effusion Cooling Holes in Aero-Engine Combustor Liners

Due to the stringent cooling requirements of novel aero-engines combustor liners, a comprehensive understanding of the phenomena concerning the interaction of hot gases with typical coolant jets plays a major role in the design of efficient cooling systems. In this work, an aerodynamic analysis of the effusion cooling system of an aero-engine combustor liner was performed; the aim was the definition of a correlation for the discharge coefficient (CD) of the single effusion hole. The data were taken from a set of CFD RANS (Reynolds-averaged Navier-Stokes) simulations, in which the behavior of the effusion cooling system was investigated over a wide range of thermo/fluid-dynamics conditions. In some of these tests, the influence on the effusion flow of an additional air bleeding port was taken into account, making it possible to analyze its effects on effusion holes CD. An in depth analysis of the numerical data set has pointed out the opportunity of an efficient reduction through the ratio of the annulus and the hole Reynolds numbers: The dependence of the discharge coefficients from this parameter is roughly linear. The correlation was included in an in-house one-dimensional thermo/fluid network solver, and its results were compared with CFD data. An overall good agreement of pressure and mass flow rate distributions was observed. The main source of inaccuracy was observed in the case of relevant air bleed mass flow rates due to the inherent three-dimensional behavior of the flow close to bleed opening. An additional comparison with experimental data was performed in order to improve the confidence in the accuracy of the correlation: Within the validity range of pressure ratios in which the correlation is defined (>1.02), this comparison pointed out a good reliability in the prediction of discharge coefficients. An approach to model air bleeding was then proposed, with the assessment of its impact on liner wall temperature prediction.

外部圧縮型超音速インテーク性能に及ぼすスリット抽気の影響

The performance of a two-dimensional Mach 1.64 external compression air intake is investigated by computational fluid dynamics. The intake model consists of a 10-degree wedge and a subsonic diffuser. The flow in and around the intake with different configurations of the slit at the diffuser entrance is calculated to examine the effect of the configurations for pressure recovery and stability of the shock system. The numerical results indicate that the natural bleed fairly improves the intake performance at subcritical operation: It improves the maximum pressure recovery and the tolerance of the mass flow rate through the diffuser to guarantee the stability of the shock. The bleed mass flow rate strongly depends on the slit configuration. Large bleed mass flow rate increases the tolerance of the diffuser mass flow rate for the shock stability. However, the presence of the slit provides no gain in efficiency of the intake at supercritical operation.

Improvements of the base bleed effect using reactive particles

A numerical study of the base drag reduction of axisymmetric body projectiles in supersonic flight using a base bleed injection is presented in this paper. Unsteady computations of compressible viscous flow have been achieved in order to investigate the coupled effect of the bleed temperature and the bleed mass flow rate on the base pressure. The idea developed in the study, consists in the addition of metallic particles in the propellant composition used to provide the additional mass injected in order to obtain the lowest base drag. Indeed, for a low mass addition, a significant increase of the mixture energy is expected due to the particles combustion. Base flow with reactive two-phase injection is then simulated. Results show the ability of the method to describe such flows and the efficiency of the particles combustion to increase the base bleed reducing drag effect.

多孔抽気を模擬するCFD用壁面境界条件モデル

In order to simulate actual behavior of bleed air flows in various air-intake operating conditions, it is necessary to consider the change in bleed mass flow rates according to the bleed plenum conditions. Wind tunnel testing was carried out for validation of the conventional Harloff’s model for the rates. The results showed that the model overestimates the bleed mass flow rates in certain cases where blowing from the bleed plenum into the main stream occurs. A new boundary condition model improved by addition of the effect of the main stream dynamic pressure is proposed and enables quantitative prediction of the bleed mass flow rates in such cases.

Visualization of a central bleed jet in an axisymmetric, compressible base flow

The central bleed jet in an axisymmetric, compressible base flow with a Mach 2.46 free stream was visualized using an acetone planar laser-induced fluorescence (PLIF) technique. Three bleed flow rates, a low-bleed case (I=0.0038) and two others that bracket the optimal bleed case (I=0.0113 and I=0.0226), were examined. The injection parameter, I, is defined here as the bleed mass flow rate normalized by the product of the base area and freestream mass flux. This study shows that the bleed jet in the low-bleed case is almost instantly deflected outward toward the outer shear layer after it exits from the bleed orifice. When I=0.0113, the bleed fluid carries enough momentum that the bleed jet remains coherent and generally aligned along the symmetry axis for approximately one base radius before it is deflected outward by the primary recirculation region. For the highest bleed rate examined (I=0.0226), the bleed jet remains coherent and aligned along the symmetry axis for approximately 2.5 base radii downstream, where the impingement of freestream fluid causes the bleed jet to symmetrically eject mass downstream. Because the behavior of the bleed jet is much different for pre- and post-optimal bleed rates, some general conclusions can be made about the effect of bleed rate on base drag. For the two lower-bleed cases, there is a base pressure increase because the bleed fluid partially isolates the primary recirculation region from the outer flow, and provides part of the mass necessary for entrainment in the outer shear layer. The bleed jet in the high-bleed case is not as effective at increasing the base pressure, because the jet is shielded from the outer shear layer by the secondary recirculation region, which exists in the annulus between the bleed orifice and the base corner.

Lag model for turbulent boundary layers over rough bleed surfaces

Boundary-layer mass removal (bleed) through spanwise bands of holes on a surface is used to prevent or control separation and to stabilize the normal shock in supersonic inlets. The addition of a transport equation lag relationship for eddy viscosity to the rough wall algebraic turbulence model of Cebeci and Chang was found to improve agreement between predicted and measured mean velocity distributions downstream of a bleed band. The model was demonstrated for a range of bleed configurations, bleed rates, and local freestream Mach numbers. In addition, the model was applied to the boundary-layer development over acoustic lining materials for the inlets and nozzles of commercial aircraft. The model was found to yield accurate results for integral boundary-layer properties unless there was a strong adverse pressure gradient. Nomenclature A = constant (26.0) in van Driest's damping function, Eq. (3) ks = equivalent sand-grain roughness height k+ = roughness Reynolds number, ksuT/v k^ = constant (0.02) in outer layer eddy viscosity model, Eq. (4) k3 = constant (0.5) in the lag model, Eq. (7) / = length scale rabl = bleed mass flow rate p = static pressure R = augmented mixing length due to surface roughness effect Re = Reynolds number M, v = velocity components in the streamwise and the normal to surface directions UT = frictional velocity *, y = coordinates in the streamwise and the normal to boundary-layer surface directions T = intermittency factor in Eq. (4), 0 < F < 1 8* = displacement thickness 6 = momentum thickness K = von Karman constant, 0.40, Eq. (3) fji — viscosity p = density v = kinematic viscosity of the fluid Subscripts e = outer region of boundary layer eq = equilibrium turbulent flow t = turbulent flow Superscripts ' = fluctuating turbulent quantity + = quantity normalized by vluT

Investigation of shock/turbulent boundary-layer bleed interactions

Investigation of shock/turbulent boundary-layer bleed interactions