Aerodynamic characteristics and mechanisms for bionic airfoils with different spacings

Abstract

In this study, the aerodynamic characteristics of multi-protuberance airfoils modeled on the fin of a humpback whale were investigated by numerically simulating the National Advisory Committee for Aeronautics 634-021 airfoils. For a Reynolds number of 1.8 × 105, the numerical simulation results obtained with no spacing between protuberances were compared with experimental values to verify the accuracy of the numerical method. The effects of different spacings on the aerodynamic performance of the airfoil at various angles of attack were investigated by setting the spacing between the two protuberances as 0.25, 0.5, and 0.75c. The results show that the lift coefficient was increased by 5%-15%, and the drag coefficient remained constant under different conditions when the spacing between the protuberances was 0.25c. The twin-protuberance airfoils with different spacings exhibited similar two-step stall characteristics. However, only the unspaced twin-protuberance airfoil had a one-sided stall. Simulations of the multi-protuberance airfoil showed that airfoils featuring spacings between protuberances exhibited good lift characteristics at large angles of attack. With an increase in the angle of attack, the lift coefficient steadily changed. Compared with the full-protuberance airfoil, the drag coefficient of the airfoil with spacing was significantly reduced.