Geometrical shape influence on energy harvesting performance of oscillating airfoil

Abstract

In recent years, as an alternative to conventional turbomachinery, flapping foils or oscillating airfoils are under increasingly active investigation to extract energy from wind/water. Their potentials for the generation of electric power are studied here computationally using a two-dimensional unsteady Navier-Stokes solver. In this study, the effect of geometrical shape variation on energy harvesting performance of oscillating airfoil have been investigated. A selective range of parameters have been investigated for symmetrical airfoils (NACA0012, NACA0015, and NACA0018), including the airfoil geometrical parameters: thickness distribution and trailing edge shapes (sharp, blunt and round); fundamental kinematics parameters, i.e. frequency oscillation (f^*=0.10-0.20) at fixed heaving and pitching amplitudes, and the effect of fluid physics (laminar flow at Re = 1100 and turbulent flow at Re = 5x105) are considered. For the turbulent simulations, the highly resolve numerical simulations (y+ ? 1) are performed at high pitch angles using the k-? SST turbulence model, which is found to model the flow separation effectively. The power-extraction efficiency has been used as the performance comparison metric to map the performance into the parametric space considered in this study. The peak efficiency for laminar case has occurred at frequency, f^*=0.14 meanwhile for turbulent case, high efficiency has occurred at frequency, f^*=0.18 and ?_0=76.3°. Less than 2% differences in power efficiency has been observed on the study of the effect of thickness distribution at low Reynolds number, while about 10 to 16% difference has been found for high Reynolds number by comparing NACA0018 and NACA0012 airfoils. Both laminar and turbulent flows show that sharp edge gives the most optimum efficiency performance, with the highest efficiency for laminar is 33.3% while for turbulent is 44.5%.
Keywords – oscillating airfoil; energy harvesting; laminar and turbulent flow field

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