Numerical study of an Undulatory Airfoil with different leading edge shape in power-extraction regime and propulsive regime

Except for providing propulsion motion, the undulating fins can also be used as one type of flow-driven energy harvester, like a wind turbine. In this paper, the baseline NACA0012 airfoil was used to obtain a series of airfoils with different leading-edge radiuses which were then used as two-dimensional simplified models of a fish body undertaking undulating motion. With the aid of CFD software, the effects of leading-edge shape and Reynolds number on the hydrodynamic characteristics of an undulatory airfoil in its energy-extraction regime and propulsion regime were studied and compared. The results indicated that the energy extraction efficiency of the undulatory airfoil with a thicker leading-edge becomes correspondingly higher at moderate to high Reynolds numbers. However, the energy extraction efficiency is hardly affected by the geometric shape changes of the undulatory airfoil leading edge at low Reynolds numbers. On the other hand, when the undulatory airfoil is in the propulsive regime, it seems that the airfoil with smaller leading-edge radius can achieve a higher propulsive efficiency which coincides with appearance traits in fish observed in nature. In addition, the propulsive performance of the undulatory airfoil can be considerably affected by its leading-edge radius at only low and moderate Reynolds numbers. (C) 2019 Elsevier Ltd. All rights reserved. Except for providing propulsion motion, the undulating fins can also be used as one type of flow-driven energy harvester, like a wind turbine. In this paper, the baseline NACA0012 airfoil was used to obtain a series of airfoils with different leading-edge radiuses which were then used as two-dimensional simplified models of a fish body undertaking undulating motion. With the aid of CFD software, the effects of leading-edge shape and Reynolds number on the hydrodynamic characteristics of an undulatory airfoil in its energy-extraction regime and propulsion regime were studied and compared. The results indicated that the energy extraction efficiency of the undulatory airfoil with a thicker leading-edge becomes correspondingly higher at moderate to high Reynolds numbers. However, the energy extraction efficiency is hardly affected by the geometric shape changes of the undulatory airfoil leading edge at low Reynolds numbers. On the other hand, when the undulatory airfoil is in the propulsive regime, it seems that the airfoil with smaller leading-edge radius can achieve a higher propulsive efficiency which coincides with appearance traits in fish observed in nature. In addition, the propulsive performance of the undulatory airfoil can be considerably affected by its leading-edge radius at only low and moderate Reynolds numbers. (C) 2019 Elsevier Ltd. All rights reserved.