Propulsion of a Plunging Flexible Airfoil using a Torsion Spring Model

The aim of the present study is to understand the mechanism of propulsion in biological flyers, initially starting from rest, using a computational analysis of the plunging motion of a flexible wing. Simulations are performed on a self-propelled flexible wing unconstrained to move in direction perpendicular to the heaving motion. A two-dimensional lumped torsional flexibility model has been developed for a multi-component system which mimics a real insect wing. Using the lattice-Boltzmann method, this model is used to investigate the role of chordwise flexibility on fluid mechanics associated with forward propulsion. The aerodynamics and vortical wake patterns at different frequencies are investigated for a range of Reynolds number and bending stiffnesses. In addition, the behavior of input power and efficiency with stiffness has been examined. This work is anticipated to pave the way towards an improved understanding of propulsion in biological flyers employing flexible wings and thereby contribute to development of micro-air vehicles employing the same concept.