Numerical Simulation of Unsteady Viscous Flow around a Flapping Wing

摘要

Unlike aircraft, a bird should generate lift and thrust at the same time by a flapping motion of a wing. In order to investigate the aerodynamic mechanism of generating lift and thrust by a flapping wing, many theoretical and experimental studies have been conducted so far. However, the mechanism has not yet been well understood. As far as the three-dimensional (3D) wing is concerned, all the theoretical studies presented so far are based on the potential flow assumption. As you can see in the flying birds, however, the amplitude of the flapping motion of the wing is very large ( for example, the flapping angle of a pigeon is about 50 deg as shown later in the example). In such a large amplitude of the flapping motion, the induced angle of attack (due to the flapping motion of a wing) exceeds easily stalling angle. This means that the discussions based on the potential flow assumption become meaningless. In the present study, the numerical simulation of unsteady viscous flow around a flapping wing has been conducted by using a 3D Navier-Stokes code and the role of the flow separation, especially, the effect of dynamic stall on the propulsive efficiency, thrust and lift of a flapping wing has been investigated.