Experimental Study on Self-Excited and Forced Oscillations of an Oblique Shock Train

Abstract

Two types of unsteady shock train motion, including self-excited oscillation and forced oscillation, were experimentally studied and compared in this work. The experiments were conducted in a rectangular isolator under Mach 3 incoming conditions. High-speed schlieren technology and high-frequency pressure measurements were adopted to do this research. The mean pressure distributions, the pressure standard deviation distributions, and the spatial frequency distributions were estimated for two types of unsteady shock train oscillations. It was found that the shock train may self-excite oscillations for Mach 3 incoming flow at relatively low frequencies (below 200 Hz) under steady backpressure conditions. With the downstream backpressure forcing, the shock train oscillated in a composite pattern, which was dominated by the imposed frequency content and coupled with the inherently self-excited frequency content. And, the self-excited oscillation was restrained, but was not eliminated, by the forced oscillation.