Experimental Feedback Control of Flow-Induced Cavity Tones

An experimental study of the application of discrete-time, linear quadratic control design methods to the cavity tone problem is described. State space models of the dy- namics from a synthetic jet actuator at the leading edge of the cavity to two pressure sensors in the cavity were computed from experimental data. Variations in model order, control order, control bandwidth, and properties of a Kalman state estimator were stud- ied. Feedback control reduced the levels of multiple cavity tones at Mach 0.275, 0.35, and 0.45. Closed loop performance was often limited by excitation of sidebands of cavity tones, and creation of new tones in the spectrum. State space models were useful for ex- plaining some of these limitations, but were not able to account for non-linear dynamics, such as interactions between tones at dierent frequencies. ow over a rectangular cavity is a well known phenomenon which aects landing gear and weapons bays on aircraft. The sound pressure levels of the tones can be very high, which can create a noise problem inside the aircraft and can destroy delicate instrumentation in the cavity itself. While the reduction of the noise levels is an important issue, the cavity tone problem is also an interesting testbed for active ow control studies. Active control of ow around an airfoil has been proposed as an alter-