Flow Around Flapping Flexible Flat Plate Wings

This study investigates the unsteady flow phenomena generated from plunging wings with varying flexibility. The experiments were conducted in a wind tunnel with forward flight conditions at a chord based Reynolds number of 5300. The wings are fabricated out of homogeneous isotropic materials with values of 55 and 1702. The conditions of these experiments are matched to previous studies in a water channel to investigate the requirement of dynamic similarity utilizing the flexible wing similarity parameter ( ). Stereo Particle Image Velocimetry is used to measure the phase-averaged flow around the wings in several spanwise planes along the wing. The flow data provides insight into the evolution of vortices formed at the leading edge of the wing. This data is also used to estimate the forces created by the wings using a momentum balance method. The measurements showed that large deflections at the tip produced strong leading edge vortices. However, when the tip-root lag is greater than 180°, the effects are adverse resulting in no leading edge vortex development. In order to understand wing flexibility further, additional experiments were performed using a laser Doppler Vibrometer to understand the modal properties for each wing with varying flexibility parameter. These studies are designed to gain further insight into future experiments that attempt to control the amount of deformation on the wing by altering the ratio of plunging (excitation) to the natural frequency.