The Aerodynamic Force of a Model Butterfly in Forward Flight

摘要

Aerodynamic force generation of a model butterfly in forward flight is studied. The method of numerically solving the Navier-Stokes equations in moving overset grids, coupled with the dynamics equations of motion, is used. In our study, at each time step, we obtain the aerodynamic forces and moments of the flapping wings and they are used to integrate the motions of the body with the Runge-Kutta method to a new time step. Then the motions of the body are added to the wings' flapping motion to get the new aerodynamic forces and moments at new time step. The results show that the vertical and thrust forces of the wings, which balance the weight and the body drag, are mainly contributed by the drag of the wings. During the downstroke, a strong 'vortex ring',consisted of the leading edge vortex and the side edge vortices, is generated. The 'vortex ring' contains a jet parallel to the wing flapping direction, and the jet produces a large instantaneous drag. The vertical force is mainly due to the drag of the downstroke, while the thrust force is mainly due to the drag of the wings in the upstroke.