Design of Flapping Airfoil for Optimal Aerodynamic Performance in Low-Reynolds Number Flows

Unsteady, viscous, incompressible flows over an airfoil under flapping motion are numerically investigated. Depending on key parameters such as Reynolds number, reduced frequency, and flapping amplitudes, a flapping airfoil could experience complex flow fields. The trailing-edge vortex plays an important role to induce inverse Karman-vortex street which is a jetlike flow on the downstream and then generates thrust. And, the leading-edge separation vortex is closely related on the propulsive efficiency. Through careful computations of several pitching, plunging, and plunging combined with pitching modes in terms of flow and/or geometry parameters, the key physical flow phenomenon dictating the aerodynamic characteristics of flapping airfoil is identified. Based on the analysis of thrust coefficient and propulsive efficiency a new airfoil shape for optimal aerodynamic performance is proposed. The improved performance of the new flapping airfoil is validated in terms of thrust coefficient and propulsive efficiency in various low-Reynolds number flow regimes.