Closed-Loop Control of Linear Supersonic Cavity Tones

Experiments in a supersonic wind tunnel studied the behavior of acoustic tones introduced by open-loop forcing, and the ability of a closed-loop controller to suppress acoustic tones. The performance of pulsed-blowing and zero-net-mass actuators was documented. By independent changes in the wind tunnel static pressure and actuator supply pressure, we showed that the amplitude of disturbances input from the actuator is proportional to the pressure difference across the actuator, and scaled with the freestream dynamic pressure. The cavity used in this experiment at M = 1.86 responded linearly to the disturbance input from the actuators. Acoustic tone amplitudes in the cavity were linearly proportional to actuator input, and nonlinear interactions between different acoustic modes (such as the formation of combination modes) were not observed. Given that the system responded linearly to open-loop forcing and the amplitude of disturbances from the actuator exceeds background disturbance levels, then closed-loop control of the Rossiter tones should be feasible using standard linear control design tools. A simple gain-phase adjustable feedback controller is used to demonstrate linear closed-loop control.