Energy harvesting and vortex wake structure of an oscillating hydrofoil at high Reynolds number

The energy extraction potential from the sinusoidal heaving and pitching motion of an elliptical hydrofoil is explored through direct numerical simulations (DNS) at a Reynolds number of 1,000 and large eddy simulations (LES) at a Reynolds number of 50,000. The LES is able to capture the time-dependent vortex shedding and dynamic stall properties of the foil as it undergoes high relative angles of attack. At a reduced frequency of fc/U_∞ = 0.1 the high Reynolds number flow has a 1.4-3.6% increase in power compared to the low Reynolds, however at fc/U_∞ = 0.15 the enhancement in power is as much as 6.7%. It is found that a stronger leading edge vortex and faster vortex convection times can enhance the vertical force coefficient to yield more power throughout a portion of the stroke in comparison with the low Reynolds simulations. The organized vortical structures of the wake in terms of vortex location and strength are analyzed for future multiple-foil array configurations via a vortex tracking algorithm.