Investigation of Physics of Large-Scale Unsteadiness of Shock Induced Turbulent Separation Using Planar Laser Imaging Methods

摘要

This project was aimed at investigating the cause of the low frequency unsteadiness of shock-induced separated flows. This was accomplished by experimentally studying a Mach 5 unswept compression ramp interaction using a combination of planar Imaging diagnostics (namely planar laser scattering and particle image velocimetry (PIV)) and fast response pressure measurements. In particular, PIV was used to investigate the relationship between turbulent velocity fluctuations in the upstream boundary layer and the unsteady separation shock behavior. It was found that positive streamwise velocity fluctuations in the upstream boundary layer correlated with downstream shock motions and negative velocity fluctuations correlated with upstream shock motions. Interestingly, only velocity fluctuations near the wall were correlated with the shock foot motion. These results are coexistent with a simple model wherein a fuller velocity profile provides increased resistance to separation and hence a downstream shock location, and variations in the shape of the velocity profile resulting from turbulent fluctuations yield changes in the shock position and hence produce the unsteady shock foot behavior.