Vortex dynamics and aerodynamic performance of highly deformable flapping wings*

Flexible wings show great potential to increase the flight performance of nature's fliers and human-engineered flying vehicles. However, the performance gain is only achieved if the proper aeroelastic conditions are met. If the flexibility is either too high or too low the aeroelasticity can impact the lift production negatively.

In this study, we present a flapping membrane wing platform and identify optimal aeroelastic parameters to achieve the highest lift production or most efficient hovering flight experimentally. Additional deformation and flow field measurements are conducted, to relate the fluid-structure interaction of the passively deforming membrane with the force production on the wing. At high wing deformations, the flow separates over the high membrane curvature instead of the wing's leading edge. At lower angles of attack, the local angle at the leading edge becomes negative and we observe the formation of a vortex on the pressure side of the wing. These two vortical structures are unique to the membrane wings. Their position relative to the wing is unfavourable which leads to dramatic losses in lift production and hovering efficiency.