Prediction of the Wake Behind a Horizontal Axis Tidal Turbine Using a LES-ALM

Abstract

A large-eddy simulation-actuator line method (LES-ALM) applied to a single horizontal axis tidal turbine is presented and validated against experimental data. At a reasonable computational cost, the LES-ALM is capable of capturing the complex wake dynamics, such as tip vortices, despite not explicitly resolving the turbine’s geometry. The LES-ALM is employed to replicate the wake behind a laboratory-scale horizontal axis turbine and achieves a reasonably good agreement with measured data in terms of streamwise velocities and turbulence intensity. The turbine is simulated at six tip speed ratios in order to investigate the rate of decay of velocity deficit and turbulent kinetic energy. In the far-wake, these quantities follow a similar decay rate as proposed in the literature with a −3/4 slope. For cases when the turbine spins at or above the optimal tip speed ratio, the levels of turbulent kinetic energy and wake deficit in the far-wake are found to converge to similar values which seem to be linearly correlated. Finally, transverse velocity profiles from the simulations agree well with those from an analytical model suggesting that the LES-ALM is well-suited for the simulation of the wake of tidal stream turbines.