ABSTRACT
Waves and tidal currents will induce motions in floating tidal turbines, which will in-turn influence the loads and hydrodynamic performance of the device. This paper explores the hydrodynamic behaviour of a floating tidal turbine oscillating in pendulum type motions. Computational Fluid Dynamics (CFD) simulations were carried out on a floating tidal turbine oscillating at various amplitudes and frequencies. The vertical variation in local relative velocity due to the pendulum-like motion causes the loading to vary around the azimuth despite the imposed uniform upstream flow. At sufficiently large, but still relatively small, amplitudes and frequencies of oscillation, the rotor experiences flow separation as it oscillates in the upstream direction, and enters the turbulent wake state when moving into the downstream direction. The rotor power generation varies in efficiency through the oscillation cycle, and deteriorates as the amplitude increases and flow separation and wake state phenomena occur.
