An Experimental Investigation of Transverse Liquid Injection in Confined Supersonic Flow over Cavities

Abstract

An experimental investigation was carried out to study the acoustic radiation of a rectangular wall mounted cavity in confined supersonic flow under the influence of transverse injection of distilled water (surrogate fuel). This work is a part of an ongoing research program to identify cavities, which will enhance mixing using acoustic radiation in supersonic combustors with liquid fuel. The free-stream Mach number was 1.5 and the cavity length to depth ratio was varied from 0.69 to 5.0. The effect of liquid injection location and injection pressure (5-20 bar) on the cavity dynamics was studied. Acoustic measurements carried out on the top wall of the test model showed shifts in oscillating frequencies and changes in amplitude due to liquid injection. Instantaneous Schlieren images were obtained to visualize the shock structures generated by liquid injection and their interaction with the shock structures generated by the cavity. The shock induced from the liquid injection changes the flow conditions at the cavity leading edge leading to changes in cavity behavior. The fluid dynamic coupling of flow conditions at cavity leading edge and cavity depth lead to increased amplitudes for few cavity depths compared to the case of absence of injection. This was experienced for cavities with L/D around 2 and the amplitude increased by 50%. Schlieren pictures indicate that a normal shock stands upstream of the cavity leading edge for the cases where increase in amplitudes was experienced.