Simultaneous Feedback Stabilization of Two Flute Modes of Similar Frequency

A multimode feedback stabilization system which separates the modes by their spatial variation has been developed and used successfully in an experiment in which the m = 1 and m = 2 flute modes can exist simultaneously with almost the same frequency in the laboratory frame. The system allows separate control of each mode and, therefore, can be a useful diagnostic tool. An interesting result is the observation of the nonlinear coupling between the m = 1 and m = 2 modes. The m = 1 mode apparently has a strong quenching effect on the m = 2 mode.