Intermittent control of cavity flow with acoustic radiation by a plasma actuator

Abstract

The self-sustained oscillations in a cavity flow with acoustic radiation are controlled by an intermittently driven plasma actuator, which induces spanwise non-uniformity of the incoming boundary layer. To evaluate the control effects, compressible flow simulations have been conducted along with wind tunnel experiments. The feedback control by driving the plasma actuator only in the time of intense sound pressure level in the cavity was performed. As a result, the sound reduction level of 11 dB was achieved, where the plasma actuator was approximately periodically switched-on and switched-off at the intermittent frequency of 50 – 100 Hz. Moreover, the influence of the intermittent frequency on the sound reduction was investigated for the control with a temporally constant intermittent frequency. It was presented that the largest reduction level of 13 dB was achieved by the control with the intermittent frequency of f_i = 200 Hz. To clarify the mechanism for this influence of the intermittent frequency on the control effects, the time variation of the incoming boundary layer and cavity flow during the intermittent period was investigated. The maximum non-uniformity of the incoming boundary layer during the control was larger for the effective control with f_i = 200 Hz compared with the control with higher intermittent frequencies. In the cavity flow controlled with f_i = 200 Hz, the vortices causing the cavity tone was constantly suppressed during the intermittent period. Meanwhile, for the case with the lower intermittent frequency of f_i = 50 Hz, weakening and reinforcing of the vortices were repeated in the intermittent period.