High Subsonic Cavity Flows Forced with Localized Arc Filament Plasma Acutators

Abstract

Engine unstart is a problem in scramjets. The shock train adjusts the incoming flow speed and pressure before it reaches the combustor. If the combustor pressure is too high the shock train is forced out of the scramjet and can potentially cause engine unstart. Cavities can be used to prevent shock movement but at hypersonic speeds it does impose a significant drag penalty. During normal operation the cavity needs to be weakly resonating but when unstart is an impending the cavity needs to be strongly resonating to trap the unstart shock. A previous study has shown localized arc filament plasma actuators can turn a strongly resonating cavity into non-resonating one. Localized arc filament plasma actuators have been used to enhance resonance in a weakly resonating cavity to establish resonance. The actuators were placed across the span of the cavity just upstream of the leading edge. The freestream flow was Mach 0.6 with a Reynolds number based on cavity depth of 2x105. Forcing sweeps of the actuators occurred near natural Rossiter modes and the effects on the cavity flow observed. Quasi-two-dimensional (i.e. the actuators are operating in phase) forcing was found to be best for resonance enhancement. Forcing near the 2nd Rossiter mode and first harmonic of the 2nd Rossiter mode amplified the tonal peak and broadband spectrum to similar sound pressure levels seen in a strongly resonating cavity, the tonal peak was at 145 dB and the broadband spectrum were nearly the same. This study in conjunction with previous work has shown localized arc filament plasma actuators have superior control of cavity flows.