The effects of the incoming turbulent boundary layer structure on a shock-induced separated flow

Abstract

An experimental study is underway to investigate the effect of the incoming turbulent boundary layer structure on separation shock unsteadiness. The flow in a Mach 5 unswept compression ramp interaction has been investigated using the primary'diagnostics of planar laser scattering (PLS) of an alcohol fog and particle image velocimetry (PIV). Double-pulse PLS imaging has been used to acquire image pairs which show the evolution of large-scale boundary layer structures as they pass through the separation shock. It was observed that while turbulent structures greatly distort the outer region of the separation shock, the shock foot does not move appreciably. Correlations between the boundary layer thickness as inferred from the PLS images and the shock motion as determined by pressure transducers mounted in the floor show no discernible relationship between the * Graduate Student, Student Member AIAA t Assistant Professor, Senior Member AIAA t Professor, Associate Fellow AIAA Copyright © 1998 by S. J. Beresh, M. Comninos, N. T. Clemens, and D. S. Dolling. Published by the American Institute of Aeronautics and Astronautics, Inc. with permission. passage of large-scale turbulent structures and the motion of the separation shock foot. PIV measurements were conducted in the incoming boundary layer to obtain ensemble averages of the streamwise velocity fluctuations conditioned upon the shock foot motion. No correlation was found between these two events. Similarly, no clear trend was observed between the incoming turbulent velocity fluctuations and the velocity of the separation shock foot. These results seem to suggest that the primary source of the separation shock unsteadiness is not the upstream boundary layer, although further work is required before this can be stated definitively.