LAUSR

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. Results of the computations are validated against experimental flume data, and show very good agreement. The high Reynolds number LES provides a direct comparison of power, forces and torques as well as vortex dynamics between the two Reynolds numbers. At a reduced frequency of $fc/U_{\infty}=0.1$ the high Reynolds number flow has a 1.4-3.6\% increase in power compared to the low Reynolds number flow, however at $fc/U_{\infty}=0.15$ 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 number simulations. The kinematics for optimal efficiency are found in the range of $h_0/c=0.5-1$ and $\theta_0=60-65$ for $fc/U_{\infty}=0.1$ and of $h_0/c=1-1.5$ and $\theta_0=75-85$ for $fc/U_{\infty}=0.15$. Although there are minor differences between the low and high Reynolds number simulations, the low Reynolds number simulations captured most of the energy harvesting dynamics, and were able to closely predict the optimal operating regime.