Group Delay in Digital Filter Induced Instability of a Two-Dimensional Airfoil Active Flutter Suppression System

The presented paper deals with the group delay in the digital filter induced instability of a two dimensional airfoil section active flutter suppression system. Firstly, the aeroelastic model of the airfoil with an ultrasonic motor actuated control surface is set up; secondly, both H-infinity and mu robust controllers are designed; and then, the group delay induced instability in wind tunnel test is presented; finally, through a combined theoretical and numerical study, the test phenomenon is well explained. Wind tunnel experiments and numerical simulations demonstrate that long enough group delay in digital filter can induce instability of flutter control system, the flutter under control will decrease first, and then become another flutter of lower frequency and moderated amplitude, and mu, controller works better than H-infinity controller on the same condition.