J024012 The numerical simulation of the effect of wing deformation on an ornithopter

Abstract

In this study we investigated the effect of wing deformation on numerical simulation of aerodynamics of ornithopters. The ornithopter we used had a pair of wings and a tail wing, and is capable to perform forward flight. The wing consisted of a rigid leading edge bars and a polymer film membrane. We measured the wing deformation with three high-speed video cameras in three different conditions: free flight, tethered flight, and "semi-tethered flight" in which the ornithopter was mounted on a linear actuator and moved forward constantly. Then, measured wing deformations were applied to a CFD (Computational Fluid Dynamics)-based simulation in which the ornithopter was fixed in a steady flow. As a result, the wing deformation measured in the free flight and the semi-tethered cases caused larger vertical force than that with the wing deformation of the tethered case. It was also found that the wing deformation of the free flight case resulted in smaller horizontal force than that of the the other cases at the latter half of downstroke. On the contrary, at the middle of upstroke, the wing deformation of the free flight case caused larger drag than that of the other cases. These results suggest that it is desirable to use a free flight model when time variation of aerodynamic forces is considered.