Fluid-Structure Interactions for a Low Aspect-Ratio Membrane Wing at Low Reynolds Numbers

摘要

Force, Particle Image Velocimetry (PIV) and high-speed Digital Image Correlation (DIC) measurements were performed on a stationary, aspect-ratio two, perimeter-reinforced membrane wing with no pre-tension or excess length at Re_c=46,000. Data were taken over the range of incidence angles from zero to twenty-five degrees. Four distinct regions of angle of attack can be defined based on mode shape, frequency and amplitude of membrane oscillations. At zero and very small incidences, large amplitude oscillations in the first mode are observed. As the angle of attack is increased the third mode becomes dominant. PIV measurements suggest that these two regions are associated with an impingement on the membrane of the shear layer that separates at the wing leading-edge. In a range of incidences which are much lower than the stall angle, higher modes are observed with very small amplitude. PIV results suggest that there is no shear layer impingement in this range. Once the shear layer mostly separates over the wing span, membrane vibrations are dominated by the second chord-wise mode, which is thought to be due to the vortex shedding phenomenon. Over part of this region there is evidence of a higher span-wise mode being present on the wing due to the influence of the tip vortices. The proximity of the two mode frequencies leads to a 'beating1 pattern in the amplitude of the membrane deformation, with possible implications for MAV flight control.