Experiments on Transonic Flutter of a Two-Dimensional Supercritical Wing with Emphasis on the Non-Linear Effects.

Kurzfassung

Flutter measurements were performed with a supercritical two-dimensional wing primarily in the transonic flow regime. The rigid wing model was mounted in a symmetrical suspension system permitting two degree-of-freedom oscillations in heave and pitch. The motion of the wing was measured non-intrusively by optical methods and steady/unsteady forces are obtained by piezo-electric balance. A non-intrusive flutter control system was applied based on a laser vibrometer and electrodynamic exciters. It permitted positive and negative feedback. The transonic dip was found to be very sharp at Ma&#610.77. The dynamic pressure for flutter at this minimum is roughly half of the subsonic value (Ma&#610.5). Three types of flutter were observed: in and near the transonic dip minimum limit cycle oscillations (LCO) in heave and pitch. The second type was pure limited cycle pitch oscillations. A little bit away from the minimum, where the dynamic pressure is slightly increased, an alternating oscillation between heave and pitch was observed. Pure heave oscillations were not found. A bifurcation diagram was plotted from four data points. The type of bifurcation seemed to be supercritical because no hysteresis effects were found. In all flutter cases the oscillations could be controlled (suppressed) using the flutter control system.