Experimental study of flow unsteadiness in a Mach 9 compression ramp interaction using a laser schlieren system

This paper demonstrates the use of a simple laser schlieren technique to obtain flow information in a two-dimensional separated compression ramp-induced shock-wave boundary-layer interaction. Tests were made at a freestream Mach number of 9 and freestream Reynolds number per unit length of 2.078 x 10(5) m(-1). The importance of this technique in studying hypersonic flows is unique since the run times of hypersonic wind tunnels are of very short duration. The method is based on the schlieren principle and uses a parallel sheet of a low-power (15 W) diode laser and an array of very fast response (4 ns) photodiodes. Although the arrangement detects an integral part of the signal from the fluctuating density gradients across the span of the flow, it yields significant insights into the details of the flow structure. The details of the flow field are discussed using time-dependent fluctuating density gradient profiles, the related power spectra and autocorrelation and cross-correlation functions in the interaction region.