Propulsive performance of a pitching foil in a side-by-side arrangement with auxiliary pitching foil

Abstract

A two-dimensional computational study is performed in the present work to simulate two NACA 0012 (National Advisory Committee for Aeronautics) airfoils pitching in a side-by-side configuration at Reynolds Number (Re) 12,000. An auxiliary airfoil with a smaller size is used to enhance the efficiency of the main airfoil. The thrust and lift coefficients of the main airfoil are quantified and compared with an isolated pitching airfoil for a range of reduced frequencies (k=1 to 8) and phase differences (?=0�to 180�) between the airfoils. The thrust force increases gradually with a maximum enhancement at an intermediate phase difference (?) between the airfoils and decreases further. The simulations cover three main flow regimes depending upon the vortex structure shed by the airfoils, i.e. (i) when both airfoil shed von K�rm�n (KV) vortex street (ii) auxiliary airfoil sheds von K�rm�n whereas main airfoil sheds reverse von K�rm�n (RKV) vortex street (iii) both airfoil sheds reverse von K�rm�n vortex street. The numerical results reveal that an auxiliary airfoil significantly changes the main airfoil's hydrodynamic characteristics compared to an isolated airfoil. Maximum thrust enhancement of 23% and maximum efficiency enhancement of 49.2% are obtained compared to an isolated airfoil. The phase difference significantly impacts the propulsive efficiency of auxiliary foil, whereas its influence is marginal on the main foil. The interaction of different wake structures shed by the auxiliary, and the main airfoil leads to the formation of the deflected jet. The jet deflection and wake width are quantified to understand the influence of an auxiliary airfoil in a side-by-side configuration with the main airfoil. The finding of this study is expected to provide new insight for developing and enhancing the performance of hydrodynamic propulsive systems by adding an auxiliary airfoil. � 2022 Elsevier Ltd