Insects Symmetrical Shot The Wing Viscous Flow Numerical Study

"Clap and fling"motions of insect wings are modeled with a pair of elliptic foils with oscillatory translating and rotating motions. The two-dimensional flow field is simulated by the Lattice Boltzmann method in a multi-block Cartesian grid and the foil boundary is processed by the bounce-back condition combined with a second-order interpolation scheme. The objective of this study is to get into physical insights on the effect of wing-wing interaction in hovering flight.First, a normal hovering motion has been simulated and the influence of two parameters, i.e., the stroke amplitude and the amplitude of pitching angle of attack, is mainly investigated. The leading edge vortex (LEV) enhanced by the Weis-Fogh mechanism contributes the lift enhancement by the wing-wing interaction. The increase of lift due to the LEV relies on the delayed stall mechanism of single flapping wing. For a large stroke amplitude, the delayed stall mechanism becomes weak and the lift decreases. The influence of wing-wing interaction on the aerodynamic forces is not only in the fling phase but also over the whole cycle of motion. The amplitude of pitching angle of attack has a significant influence on the time-averaged lift and power coefficients. Under certain values, the proportion between the time-averaged lift and power coefficients is optimized.The ground effect of clap and fling hovering leads to large enhancement of the lift and the proportion of time-averaged lift coefficient versus power coefficient. For large stroke amplitude, the strength and range of the ground effect is enhanced. The mechanism of ground effect is different with the heights. At small height, the trailing edge vortex of the foil is deformed. At large height, the mechanism of ground effect is the interaction of jet induced by the hovering flight with the bottom surface.