SUMMARY OF SUBSONIC-DIFFUSER DATA
Subsonic-diffuser data - exit flow, boundary-layer control, and inlet velocity
BOUNDARY LAYER CONTROL↗
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Analytical and experimental studies of a short compact subsonic diffuser for a two-dimensional supersonic inlet
An experimental study of a two-dimensional supersonic inlet with a short compact subsonic diffuser, length to exit diameter (dl/d) ratio of 1.25, was conducted to investigate the impact of the short diffuser on inlet performance at low speeds and to assess the diffuser subsonic performance for a simulated diffuser flow corresponding to high-speed inlet conditions near the design flight Mach number of 2.2. For the low-speed testing, a drooped lip was employed to improve the inlet performance at a high angle of attack. For the simulated high-speed testing, air was blown through slots or discrete nozzles as an active boundary-layer control. The results from the low-speed performance test were compared with the results from a previous test program on the same inlet with a long subsonic diffuser (dl/d = 4.5). The comparison indicates that inlet recovery was not affected by the use of the short diffuser for either the baseline (no droop) or the drooped cowl lip configuration. However, the inlet baseline distortion for the short diffuser configuration was substantially higher than for the long diffuser. A comparison of the two configurations with a 70 deg drooped lip showed no significant difference in distortion. For the portion of the experimental program in which diffuser conditions for high-speed flight were simulated, diffuser-induced flow separation occurred. This separation was predicted from an analytical study that used the Hess potential flow panel method and the Herring two-dimensional boundary-layer analysis computer codes. The flow separated mainly on the diffuser ramp. Subsequent tests in which boundary-control systems were utilized showed that blowing with either slots or discrete nozzles could suppress the flow separation in the short subsonic diffuser, thereby substantially improving the diffuser performance.
Iek, Chanthy↗
The Performance of a Subsonic Diffuser Designed for High Speed Turbojet-Propelled Flight
An initial-phase subsonic diffuser has been designed for the turbojet flowpath of the hypersonic x43B flight demonstrator vehicle. The diffuser fit into a proposed mixed-compression supersonic inlet system and featured a cross-sectional shape transitioning flowpath (high aspect ratio rectangular throat-to-circular engine face) and a centerline offset. This subsonic diffuser has been fabricated and tested at the W1B internal flow facility at NASA Glenn Research Center. At an operating throat Mach number of 0.79, baseline Pitot pressure recovery was found to be just under 0.9, and DH distortion intensity was about 0.4 percent. The diffuser internal flow stagnated, but did not separate on the offset surface of this initial-phase subsonic diffuser. Small improvements in recovery (+0.4 percent) and DH distortion (-32 percent) were obtained from using vane vortex generator flow control applied just downstream of the diffuser throat. The optimum vortex generator array patterns produced inflow boundary layer divergence (local downwash) on the offset surface centerline of the diffuser, and an inflow boundary layer convergence (local upwash) on the centerline of the opposite surface.
Biesiadny, Thomas J.↗
Dynamic distortion in a short s-shaped subsonic diffuser with flow separation
An experimental investigation of the time varying distortion at the diffuser exit of a subsonic HiMAT forebody and inlet was conducted at Mach 0.9 in the Lewis 8 by 6 foot Supersonic Wind Tunnel. A transitory separation was detected within the subsonic diffuser. Vortex generators were installed to eliminate the flow separation. Results from a study of the instantaneous pressure variations at the diffuser exit are presented. The time unsteady total pressures at the diffuser exit are computer interpolated and presented in the form of a movie showing the transitory separation. Limited data showing the instantaneous distortion levels are also presented. Previously announced in STAR as N83-26838
Stumpf, R.↗
Use of Subsonic Diffuser Mach Number as a Supersonic-Inlet Control Parameter
A Mach number measured in the subsonic diffuser was used experimentally as the inlet control parameter of a bypass control system for an axisymmetric supersonic inlet operated in combination with a J34 turbo-jet engine at Mach numbers from 1.6 to 2.0. The control maintained the inlet in either critical or supercritical operation, and, when set for critical diffuser operation, the control recovered from disturbances that placed the inlet in both subcritical buzz and supercritical operation. A slotted-rake orifice gave a more representative value of subsonic diffuser Mach number than the single total-pressure probe used as a control input.
Whalen, Paul P↗
Navier-Stokes simulation of flow through a highly contoured subsonic diffuser
The flow through a highly offset subsonic diffuser with cross-sectional profiles that varied from rectangular at the duct entrance to circular at the engine face was numerically simulated. A multizonal approach combined with a two-grid topology was used to represent both the internal and external flowfields, and an implicit, approximately-factored, partially flux-split finite-difference algorithm was used to solve the three-dimensional thin-layer Navier-Stokes equations. The computed static pressures along the inlet wall and total pressures on the engine face were compared with experimental data. In addition, the overall flowfield within the duct was examined in detail. Good agreement is shown between experiment and computations, with the limiting factor being the lack of a reliable turbulence model for internal flow problems.
Chyu, W. J.↗
A Full Navier-Stokes Analysis of Subsonic Diffuser of a Bifurcated 70/30 Supersonic Inlet for High Speed Civil Transport Application
A full Navier-Stokes analysis was performed to evaluate the performance of the subsonic diffuser of a NASA Lewis Research Center 70/30 mixed-compression bifurcated supersonic inlet for high speed civil transport application. The PARC3D code was used in the present study. The computations were also performed when approximately 2.5 percent of the engine mass flow was allowed to bypass through the engine bypass doors. The computational results were compared with the available experimental data which consisted of detailed Mach number and total pressure distribution along the entire length of the subsonic diffuser. The total pressure recovery, flow distortion, and crossflow velocity at the engine face were also calculated. The computed surface ramp and cowl pressure distributions were compared with experiments. Overall, the computational results compared well with experimental data. The present CFD analysis demonstrated that the bypass flow improves the total pressure recovery and lessens flow distortions at the engine face.
Kapoor, Kamlesh↗
Calculation of Turbulent Subsonic Diffuser Flows Using the NPARC Navier-Stokes Code
Axisymmetric subsonic diffuser flows were calculated with the NPARC Navier-Stokes code in order to determine the effects various code features have on the flow solutions. The code features examined in this work were turbulence models and boundary conditions. Four turbulence models available in NPARC were used: the Baldwin-Lomax algebraic model, the Baldwin-Barth one-equation model, and the Chien kappa-epsilon and Wilcox kappa-omega two-equation models. The three boundary conditions examined were the free boundary, the mass flux boundary and the subsonic outflow with variable static pressure. In addition to boundary condition type, the geometry downstream of the diffuser was varied to see if upstream influences were present. The NPARC results are compared with experimental data and recommendations are given for using NPARC to compute similar flows.
Dudek, J. C.↗
Computational Study of Separating Flow in a Planar Subsonic Diffuser
A computational study of the separated flow through a 2-D asymmetric subsonic diffuser has been performed. The Wind Computational Fluid Dynamics code is used to predict the separation and reattachment behavior for an incompressible diffuser flow. The diffuser inlet flow is a two-dimensional, turbulent, and fully-developed channel flow with a Reynolds number of 20,000 based on the centerline velocity and the channel height. Wind solutions computed with the Menter SST, Chien k-epsilon, Spalart-Allmaras and Explicit Algebraic Reynolds Stress turbulence models are compared with experimentally measured velocity profiles and skin friction along the upper and lower walls. In addition to the turbulence model study, the effects of grid resolution and use of wall functions were investigated. The grid studies varied the number of grid points across the diffuser and varied the initial wall spacing from y(sup +) = 0.2 to 60. The wall function study assessed the applicability of wall functions for analysis of separated flow. The SST and Explicit Algebraic Stress models provide the best agreement with experimental data, and it is recommended wall functions should only be used with a high level of caution.
DalBello, Teryn↗
The effect of velocity overshoot on the performance of magnetohydrodynamic subsonic diffusers
The effect of velocity overshoot, a velocity distribution encountered in magnetohydrodynamic channels with peak velocity near the wall instead of at the center, on the performance of two-dimensional subsonic diffusers was investigated. For the simplified conditions analyzed in this paper it was found that the ratio of peak-to-centerline velocity increases along the diffuser for a diffuser half angle greater than some critical value. It was also found that irrespective of the accompanying inlet temperature distribution the wall shear stress and the wall heat flux is substantially larger when the inlet velocity profile has an overshoot than that for a fully developed turbulent inlet velocity profile.
Greywall, M. S.↗
PERFORMANCE OF AN INLET HAVING A VARIABLE-ANGLE TWO-DIMENSIONAL COMPRESSION SURFACE AND A FIXED-GEOMETRY SUBSONIC DIFFUSER FOR APPLICATION TO REDUCED ENGINE ROTATIVE SPEEDS- MACH NUMBERS 0.66, 1.5, 1.7, AND 2.0
Air inlet for turbojet engines having variable angle two-dimensional compression surface and fixed-geometry subsonic diffuser
TURBOJET ENGINE↗
Dynamic Distortion in a Short S-Shaped Subsonic Diffuser with Flow Separation
An experimental investigation of the time varying distortion at the diffuser exit of a subscale HiMAT forebody and inlet was conducted at Mach 0.9 in the Lewis 8 by 6 foot Supersonic Wind Tunnel. A transitory separation was detected within the subsonic diffuser. Vortex generators were installed to eliminate the flow separation. Results from a study of the instantaneous pressure variations at the diffuser exit are presented. The time unsteady total pressures at the diffuser exit are computer interpolated and presented in the form of a movie showing the transitory separation. Limited data showing the instantaneous distortion levels is also presented.
Stumpf, R.↗
Experimental investigation of water injection in subsonic diffuser of a conical inlet operation at free-stream Mach number of 2.5
A spike-type nose inlet with sharp-lip cowl was investigated at a free-stream Mach number of 2.5 with water injection in its 16-inch diameter, 11-foot-long subsonic diffuser section. Inlet total temperature of exit with liquid-air ratios of about 0.04 with no apparent change in the critical pressure recovery. The observed temperature drops were less than the theoretically predicted values, and the amount of water evaporated was 35 to 50 percent less than that theoretically possible.
Beke, Andrew↗
Computer program calculates peripheral water injection cooling of axisymmetric subsonic diffuser
Digital computer program calculates the cooling effectiveness and flow characteristics resulting from the mixing of a cool liquid injectant /water/ with a hot sonic or subsonic gas stream /hydrogen/. The output of the program provides pressure, temperature, velocity, density, composition, and Mach number profiles at any location in the mixing duct.
Grey, J.↗
Dynamic distortion at the exit of a subsonic diffuser of a mixed compression inlet
Measuring distortion characteristics at engine face station of axisymmetric inlet
Kostin, L. C.↗
Augmentation of heat transfer by subsonic diffusion at a nearly separated state
Measurements of mean velocity, turbulence intensity, and wall heat transfer were obtained in a 13 deg total angle of divergence conical diffuser coupled to a constant diameter recovery section. The results indicated that the boundary layer was in a nearly separated state. Turbulence intensity levels approaching 0.4 were observed in the latter stages of diffusion. The convective heat transfer was always equal to or higher than corresponding values for fully developed pipe flow at the same Reynolds number. The augmentation in heat transfer was greatest during the latter stages of diffusion where the Stanton number was nearly three times the pipe flow value.
Boldman, D. R.↗
Effect of velocity overshoot on the performance of magnetohydrodynamic subsonic diffusers
The evolution of an overshoot velocity distribution was studied in a plane two dimensional diffuser as a function of diffuser divergence angle. The diffuser performance for velocity overshoot was compared to that for a fully developed inlet velocity profile. Results indicate that the ratio of peak-to-center line velocity increases along the diffuser for a diffuser half angle greater than some critical value. It was also found that irrespective of the accompanying inlet temperature distribution, the wall shear stress and the wall heat flux is substantially larger when the inlet velocity profile has an overshoot than that for a fully developed inlet velocity profile.
Greywall, M. S.↗
An analytical and experimental study of a short s-shaped subsonic diffuser of a supersonic inlet
A subscale HiMAT forebody and inlet was investigated over a range of Mach numbers to 1.4. The inlet exhibited a transitory separation within the diffuser but steady state data indicated reattachment at the diffuser exit. A finite difference procedure for turbulent compressible flow in axisymmetric ducts was used to successfully model the HiMAT duct flow. The analysis technique was further used to estimate the initiation of separation and delineate the steady and unsteady flow regimes in similar S-shaped ducts.
Neumann, H. E.↗