Computational investigation of insect-based flapping wings for micro air vehicle applications

Abstract

In this study, a computational fluid dynamics analysis was performed on bio-inspired micro aerial vehicle scale rigid flapping wings. The computational fluid dynamics analysis used a compressible unsteady Reynolds Averaged Navier–Stokes solver with low-Mach number preconditioning to study the complex, highly vortical, three-dimensional flow of low aspect ratio flapping wings at micro aerial vehicle-scale Reynolds numbers. The wing was flapped at a constant 5 Hz flap frequency at a mean chord reference Reynolds number of 25,000. The flapping and pitching kinematics were set to match those of a previous experimental study resulting in a constant flap stroke of 107° at translational pitching angles of 40°, 50°, and 60°. The force and flowfield measurements of the previous flapping-wing experiment were used for the validation of the 3D computational fluid dynamics model. The objectives of this effort were to understand the unsteady aerodynamic mechanisms and their relation to force production and aerodynamic efficiency on a rigid wing undergoing an insect-type flapping motion with passive pitching kinematics. Overall, the computational fluid dynamics results showed good agreement with the measured experimental force data. Additionally, the computational fluid dynamics simulation was able to adequately predict the process of leading edge vortex formation and shedding observed during experimentation. A vorticity summation approach used to calculate the strength of the leading edge vortex from the experimental measurements and from the computational fluid dynamics predicted flowfields showed comparable results. The computational fluid dynamics results were utilized to further analyze the differences in the flowfield and leading edge vortex formation for the three pitch angles tested as well as the instantaneous aerodynamic loads and aerodynamic power.