Measurement of the shear layer over a cavity with and without upstream mass injection

Measurements were carried out in the shear layer over a cavity with a free stream Mach number of 0.5 and upstream mass injection. Mass injection rates of 0.05, 0.10 and 0.15 lb/sec were used. Local pressure measurements were made at the cavity leading and trailing edges using calibrated five hole cone probes. In addition, dynamic measurements were taken of the acoustic oscillations inside the cavity.

The shear layer for the tunnel nominal operating condition was found to be relatively thick (approximately one inch) and thus no significant instabilities (Kelvin Helmholtz) formed once the cavity was installed. Consequently the magnitudes of the cavity acoustic oscillations observed were very small. Measurements from the cone probes also indicated a variation in local static pressure in the shear layer when upstream mass injection is employed. Finally, it was observed that the cavity edge vortices were modified by the mass injection, but due to the absence of oscillations at nominal flow conditions, the details of this interaction could not be evaluated in detail.