Unsteady Aerodynamics of Membrane Airfoils

Abstract

An experimental study of unsteady aerodynamics of two-dimensional membrane airfoils has been conducted. Measurements of membrane shape with a high-speed camera were complemented with the measurements of unsteady velocity field with a Particle Image Velocimetry (PIV) system and flow visualization. Vibrations of the membrane and mode shapes were investigated as a function of angle of attack and free stream velocity. While the mean membrane shape is not very sensitive to angle of attack, the amplitude and mode of the vibrations of the membrane depend on the relative location and the magnitude of the unsteadiness of the separated shear layer. The results indicate strong coupling of unsteady flow with the membrane oscillations. There is evidence of coupling of membrane oscillations with the vortex shedding in the wake, in particular, for the post-stall incidences. Comparison of rigid and flexible membrane airfoils shows that the flexibility might delay the stall.