Effects of wing shape, aspect ratio and deviation angle on aerodynamic performance of flapping wings in hover

Thisnumerical study is focused on assessing the effect on theaerodynamic hovering performance of wing shapes defined by the radius of the first moment of the wing area (r1¯) and aspect ratio (AR). In addition, the effect of introducing a deviation angle in thekinematics is examined. The performance ofr1¯=0.43, 0.53, and 0.63 wings with AR of 1.5, 2.96, 4.5, and 6.0 is investigated atReynolds numbers (Re) = 12, 400, and 13 500. The performance trends of the wing shapes have been observed to be independent of Re for both 2-angle and 3-anglekinematics. This is because high suctionpressures associated with the leading-edgevortex are predominantly spread in the distal (away from the wing root) and leeward regions (towards the trailing-edge) of high flapping velocities for all the cases. While the deviation angle is detrimental to the production of lift and power economy (PE, defined as the ratio of the mean lift coefficient to the meanaerodynamic power coefficient) at Re = 12 due to strongviscous effects, it improves PE at Re = 400 and 13  500. A high instantaneous angle of attack at the stroke reversal results in high lift peak for 3-anglekinematics but its effect at Re = 400 and 13  500 is attenuated by strong vortical structures on the underside of the wing. Maximum PE is achieved at AR = 2.96, as a low AR wing does not produce enough lift and high AR wings consume moreaerodynamic power. Although the lift is maximized using highr1¯ and AR wings, our results show that low...

Source: Physics of Fluids - November 2, 2016 Category: Physics Authors: Aamer Shahzad, Fang-Bao Tian, John Young and Joseph C. S. Lai Source Type: research