Control of pressure oscillations in deep cavities excited by grazing flow

Grazing flow over a deep cavity can result in acoustic resonance characterized by a standing wave-vortex feedback loop. Control of cavity resonance has potential impact in stealth aircraft and aircraft weapons bay applications, where periodic stress loading can cause material fatigue failure or damage sensitive instrumentation. A previous perturbation analysis of the fundamental equations of motion for a fluid system motivates a control method based on interaction of an external source of momentum (force) with cavity velocity fluctuations. Through proper placement of stationary control screens (force addition) within the resonant cavity in laboratory experiments, the cavity rms pressure amplitude was significantly reduced without interfering with the approaching boundary layer. Reductions in cavity base spectral peaks of up to 26 dB were achieved. Both single vortex (onequarter mode shape) and double vortex (three-quarter mode shape) cases were controlled. Placement of control screens at locations of maximum velocity fluctuation yields optimum control for force addition.