Effects of group delay in digital filter on stability of an active flutter suppression system

The paper reveals the effects of the group delay in a digital filter on the stability of an active flutter suppression system for a 2 dimensional airfoil section. The wind tunnel tests show that the active flutter suppression system becomes unstable at very slow flow speed if the group delay of the digital filter is long enough. In the wind tunnel tests of flutter suppression, the flutter amplitude under control often decreases at first as expected, and then the other self-excited vibration with lower frequency and moderated amplitude appears. The paper well explains such a phenomenon through a combined theoretical and numerical study. Both wind tunnel tests and numerical simulations demonstrate that the group delay greatly affects the above unstable motion, and that both the amplitude and frequency of the new self-excited vibration will increase with the group delay.