A Numerical Study of Aerodynamic Force Generation Mechanism for 2-D Insect Wing Motion

Numerical simulations are conducted to investigate of aerodynamic force generation for the “figure-of-eight” motion of 2-D insect wing. Wing motion is referred to Dipteran fly Phormia Regina, which was observed from the tethered flight experiment under freestream condition. Numerical simulation shows a very complex flow feature and unexpected large amount of aerodynamic force. Lift is mainly generated due to effective angle of attack during downstroke motion. On the other hand, the large amount of thrust is generated abruptly at the end of upstroke motion. Vortical structure in the wake and the pressure field around the airfoil are examined to uncover this thrust generation. Unlike the periodic inverse Karman vortex shedding which is used to explain the thrust generation of periodic oscillating airfoil, vortex pairing mechanism is observed. This mechanism induces a strong jet in the region between two vortices. From the pressure field directly, the large amount of thrust could be explained by a vortex staying in front of airfoil. Through the numerical computation for each component of “figure-of–eight” motion, the rotation is revealed the most important to generate thrust. Conclusively, circulation due to rotation plays the major role in thrust generation. This mechanism is verified by comparing time-averaged lift and changing rotation center.