In order to investigate the impact of airfoil thickness on flapping performance, the unsteady flow fields of a family of airfoils from an NACA0002 airfoil to an NACA0020 airfoil in a pure plunging motion and a series of altered NACA0012 airfoils in a pure plunging motion were simulated using computational fluid dynamics techniques. The “class function/shape function transformation“ parametric method was employed to decide the coordinates of these altered NACA0012 airfoils. Under specified plunging kinematics, it is observed that the increase of an airfoil thickness can reduce the leading edge vortex (LEV) in strength and delay the LEV shedding. The increase of the maximum thickness can enhance the time-averaged thrust coefficient and the propulsive efficiency without lift reduction. As the maximum thickness location moves towards the leading edge, the airfoil obtains a larger time-averaged thrust coefficient and a higher propulsive efficiency without changing the lift coefficient. 1. Introduction Since the Micro Air Vehicle (MAV) was generally defined by the Defense Advanced Research Projects Agency (DARPA) in 1997 [1], the Flapping Wing MAV (FWMAV) has been receiving more and more attention from military and civilian application domains. There is therefore an increasing interest to understand the aerodynamics of the flapping wing by experimental and numerical methods [2]. The first researchers who observed the unsteady flow dynamic characteristics of a flapping wing are Knoller [3] and Betz [4], and in the middle of 1930s, von Kármán and Burgers gave a theoretical explanation for the different patterns of a large-scale drag-indicative wake and a thrust-indicative wake [5]. It reinterested fluid scientists and biologists about two decades ago and now is a very active research area. Ellington gave a very comprehensive description of the insect hovering aerodynamics and unsteady aerodynamic effects were highlighted in these good series papers in 1984 [6]. Anderson et al. showed that oscillating foil could have a very high propulsive efficiency, as high as 87%, under specific conditions by water tunnel experiments [7]. Dickinson et al. demonstrated three distinct mechanisms, delayed stall, rotational circulation, and wake capture in enhanced aerodynamic performance of insects using a robotic fly apparatus [8]. To investigate the flow field and effects of flapping parameters on the thrust generation and the propulsive efficiency numerically, an unsteady panel method [9], and Navier-Stokes equations computations [10–15] have been employed during past decade,
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