ANALYSIS OF AERODYNAMIC COUPLING EFFECT IN CLOSE FORMATION FOR FLAPPING WINGS

This work explores the unsteady interaction between the streamwise vortices and the follower in a V-shaped close flapping wings formation. The advanced high fidelity LBM simulation and finite explicit dynamic solver are used to calculate the fluid structure interaction. First, the vortex effect during flapping process of flexible wing shows that the suction side adsorption effect after LEV formation will increase the lift. Due to the existence of angle of attack, the structure and aerodynamic characteristics of the LEV are different. In addition, the wing buffeting is caused by the breakdown of LEV near the median of stroke. Second, the flow structure is obviously different when the spatial phase is in phase. The spatial drift of follower's TIV, the delay of vortex shedding and the secondary vortex structure indicate that the coupling effect with incident vortex is strong. But in other temporal phases, these unsteady phenomena weaken or disappear, and are replaced by the finite time collision between the wing and the incident vortex. By comparing the aerodynamic load curves, it is found that the lift is significantly increased and the net thrust is decreased most in the same phase. However, this change is obviously weakened in other phases. The smaller the spatial phase difference is, the more obvious the aerodynamic effect is. This indicates that the coupling form of aerodynamic effect may exist between the close formation of flapping wing and the specific temporal phase when the position of two aircraft is fixed.