Experiments on Control of Limit-Cycle Oscillations in a Typical Section

Abstract

The experimental application of active control to reduce or eliminate limit-cycle oscillations in a typical section airfoil is presented. The test rig consists of a three-degree-of-freedom typical section which has free play in the e ap restoring stiffness. Such a free play was intended to mimic that associated with control surface mechanism backlashinarealsystem.Controliseffectedby meansofanactuatoractingonthee ap.AlinearquadraticGaussian optimization scheme is used to design a compensator that will accomplish three goals: 1 ) reduce or eliminate limitcycle oscillations, 2 ) increase the e utter boundary, and 3 ) be robust to variations in the e ow velocity. Although the typical section isa nonlineardynamicsystem, thecontrol system design wasbased on thelineartypical section with no freeplay. The results presented indicatethat each ofthesegoalswas accomplished. More specie cally, limit-cycle oscillations were eliminated, the e utter velocity was increased by 17%, and the control system was stable over a wide range of e ow conditions.