Control of Pressure Loads in Geometrically Complex Cavities

The need to reduce the fluctuating surface pressure loads in realistic three-dimensional cavity configurations is clear for many applications. In this paper, we describe the results of an experimental study that examined the properties of flow over a highly three-dimensional cavity, which included angled side walls and a sloped floor. The unsteady pressure measurements revealed that the primary spectral properties, such as the frequencies of the cavity tones, are very similar to those of simpler, rectangular cavities. The study also explored the effects of different active fluidic injection methods, at the cavity leading edge, on the unsteady loads generated in the cavity. Specifically, the two active suppression concepts examined were microjets and rectangular slots at the leading edge. Both concepts showed significant reductions in the fluctuating surface pressures, upwards of 50% on the cavity aft wall, with very modest amounts of mass flowing through the injectors. When appropriately scaled for full-scale applications, the actuator mass flux required falls well within the practical range for most aircraft. Different angles for the fluidic Injection were also examined and maximum reductions were observed when injection was perpendicular to the approaching freestream flow. Additionally, the best blowing configurations were found when the injectors did not fully span the leading edge of the cavity. The reductions observed in the fluctuating surface pressure levels resulted from decreases in both the broadband and resonant features of the surface pressures. By conducting these experiments at two different facilities and over a range offreestream dynamic pressures and temperatures, this study also demonstrated that appropriate scaling of the spectral features can be achieved. This allows for the expansion of the results presented here to larger (and different) scale studies and ultimately to full-scale applications.