K. Suzuki, T. Inamuro

Kyoto University, Japan



The flapping flight of tiny insects such as a butterfly is of fundamental interest not only in biology itself but also in its practical use for the development of micro air vehicles (MAVs). It is known that a butterfly flaps downward for generating lift force and backward for generating thrust force. In this study, we consider a simple butterfly-like wing model whose body is a thin rod and wings are rectangular. The wing kinematics of the model is simplified, and we investigate the lift and thrust generation by the butterfly-like wing model by using the immersed boundary-lattice Boltzmann method (IB-LBM). Firstly, we compute the lift force, the thrust force, and the power when the body of the model is fixed. As results, we obtain the time-averaged lift force and the thrust force induced on the wings. Then, we evaluate the efficiency defined as the ratios of the lift force and the thrust force to the power for Reynolds numbers in the range of 100 – 1000. Secondly, we simulate the free flight of the model in the air under the gravity. We obtain the maximum weight which can be supported by the lift force against the gravity for Reynolds numbers in the range of 100 – 1000.