Effect of motion trajectory on the aerodynamic performance of a flapping airfoil

In this paper, the influence of the motion trajectory on the aerodynamic performance of a flapping airfoil is numerically investigated. The airfoil synchronously performs a rotating motion (pitch), a horizontal motion (surge) and a vertical motion (plunge). The motion trajectory can be modified by changing the relative frequency of surging motion (k), the amplitude of surging motion (lm) and the phase difference between pitch and surge (φ). To perform the numerical simulations, a NACA0012 airfoil is employed. A low Reynolds number (Re=500) is selected for small creatures and flapping MAVs. As compared with the traditional motion, it is observed that the figure-of-eight motion trajectory has a promotion for the thrust and propulsive efficiency, and the lift is improved when the relative surging frequency k is an odd number with the specified phase difference. In addition, the phenomenon of multiple vortices and resultant vortex capture appears when the surging motion is added, which is helpful for the improvement of thrust.