Numerical simulation of unsteady aerodynamic characteristics of the three-dimensional composite motion of a flapping wing based on overlapping nested grids

Abstract

Numerical simulations of the unsteady aerodynamic characteristics of the flapping wing composite motion are performed. To avoid negative grid sizes arising with the use of a dynamic grid and leading to divergences in the simulation and to errors in the results, an overlapping nested grid is used for the flow field background, wing, and fuselage structure. The analysis is based on the Navier-Stokes equations (N-S) and the pressure-velocity coupling method, while spatial dispersion is handled using the second-order finite volume and the adaptive step size solving strategy. The lift and resistance generated by the wing for different combinations of flow velocity, flutter frequency and amplitude, and torsion angle are determined, and the aerodynamic efficiency and flow fields are compared to find the flapping parameters that give the best aerodynamic efficiency. The simulation results show that the aerodynamic lift of a flapping wing can be greatly increased by increasing the flapping frequency, while, for a fixed frequency, the lift can be further increased by increasing the flapping amplitude, although by only a small amount. Increasing the torsion angle in the flapping of the wing can also increase the lift, but the aerodynamic efficiency will be reduced if this angle is too large. Thus, an appropriate selection of flapping wing motion parameters can effectively increase the flight lift and improve the aerodynamic efficiency.