Suppression of flow-induced pressure oscillations in cavities

Experimental methods for suppressing flow-induced pressure oscillations in a shallow cavity resulting from tangential flows over the cavity are described. The effects of manipulating the shear layer over the cavity leading edge are examined. Static and oscillating fences and steady and pulsating flow injection at the leading edge are studied for their effect on cavity sound pressure levels. Both subsonic and supersonic flow conditions are considered. Of the methods tested, static fences at the leading edge were found to provide the most suppression. Suppression was dependent on the frequency mode and the flow Mach number. Nomenclature a = speed of sound D = cavity depth / = frequency k = vortex convection velocity to freestream velocity ratio L = cavity length M = Mach number m = frequency mode number P = pressure P0 = stagnation pressure Re = Reynolds number, Uxlv S = Strouhal number S * = modified Strouhal number U = freestream velocity x = distance from nozzle exit Z = cavity span, lateral dimension a = phase delay parameter y = ratio of specific heats 8 = boundary-layer thickness v = kinematic viscosity