Experimental Study of Supersonic Entrainment Using a Cavity

The effect of wall-mounted three-dimensional cavities on the entrainment of gaseous injectant into a supersonic stream of Mach number 1.7 is studied. Entrainment induced by flow unsteadiness, turbulence, and exchange of fluid between the cavity and mainstream flow has been investigated. To clarify the influence of the ratio of cavity length to width L/W on the fluid dynamic behavior, cavities of L/W ratios between two and four were applied at a constant length-to-depth ratio L/D. Acoustic oscillations generated from the cavity were observed to have profound impact on mass exchange between the cavity and the freestream flow. These acoustic oscillations were in turn found to be dependent on the L/W ratio of the cavity. Shift in dominant acoustic mode was observed as the L/W ratio was changed from three to four. Spillage of the shear layer over the cavity walls and turbulence induced in the cavity were probed by measuring velocity using laser Doppler velocimetry. Entrainment of secondary gaseous injection into the main flow from the cavity was also observed to depend on the cavity L/W ratio.