EXPERIMENTAL AND NUMERICAL STUDY ON PSEUDO-SHOCK STRUCTURES IN A MIXED COMPRESSION RECTANGULAR SUPERSONIC INTAKE

Date

2023-7-24

Author

Özer, Ali Can

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This study investigates the characteristics of pseudo-shocks, which are complex flow structures related to shock wave boundary layer interactions (SWBLI) in a mixed compression, rectangular, supersonic intake. Wind tunnel experiments and numerical simulations are conducted to examine the pseudo-shock structures under different conditions, including variations in Mach number and bleed configurations. The experiment approach involves measuring pressure distribution along and at the exit of the intake and visualizing the pseudo-shocks using the high-speed shadowgraphy technique at various levels of back pressure throttling, generated with a back pressure valve. The oscillatory behaviour of the pseudo-shocks during the dwell time of the back pressure valve is analyzed, and the effects of back pressure throttling transition on shock structures and pressure distribution are examined. Moreover, the hysteresis behaviour, resulting from the throttling direction of the back pressure valve, is examined. Further, characteristics diagrams are obtained, and the performance of the air intake test items and the modes of operations are examined. The numerical simulations utilize Menter’s Shear Stress Transport (SST) and Baseline (BSL) k-ω turbulence models, with a focus on investigating the models' predictive capabilities for pseudo-shocks and examining the flow field within the intake. Moreover, the effect of a parameter related to the stress-limiter of the SST model is also investigated. Comparison with the experimental data is done using both the shadowgraph images and the pressure measurement data. The experimental results show that, as the back pressure valve proceeds, some transitions lead abrupt changes in the shock structures such as sudden change of the orientation of the shock-train and separation or attachment of sonic lines on the ramp and cowl surfaces. Furthermore, those points of abrupt changes are also prone to exhibit hysteresis behaviour. The oscillatory nature of the pseudo-shocks can cause the first shock of the pseudo-shock to oscillate with a displacement amplitude of 45% of the throat height of the intake. As the pseudo-shock structures start to interact with the bleed region, the maximum amount of displacement of the shocks during oscillations decreases. The numerical simulations show that the relative sizes of the separation bubbles on the cowl and ramp side are important in determining the orientation of the shock-train. Additionally, the comparison between the simulation results and the experimental data revealed that there are noticeable differences between the SST and BSL models at lower throttled conditions. The stress-limiter parameter was also found to have an apparent impact on the simulation results. However, as the throttling increases and the mode of operation approaches the critical, the disparity between the results decreases.

Subject Keywords

Supersonic Intake, Shock Wave Boundary Layer Interaction, Pseudo-Shock, Wind Tunnel Tests, Computational Fluid Dynamics

URI

https://hdl.handle.net/11511/104900

Collections

Graduate School of Natural and Applied Sciences, Thesis