|The Performance Assessment of Wave and Tidal Array Systems (PerAWaT) project, launched in October 2009 with £8m of ETI investment. The project delivered validated, commercial software tools capable of significantly reducing the levels of uncertainty associated with predicting the energy yield of major wave and tidal stream energy arrays. It also produced information that will help reduce commercial risk of future large scale wave and tidal array developments.
This deliverable presents the simulation and analysis of the influence of surface waves on the performance, loading and wake of a marine turbine. A full scale rotor is simulated using three-dimensional Computational Fluid Dynamics (Ansys Fluent) in which the blade resolved rotor is embedded within a rotating sliding mesh. The turbine is subjected to a sheared flow profile, together with waves of varying wave length, wave height and yaw angle. Performance is assessed over a range of tip-speed-ratios.
It is found that surface waves have a detrimental effect on the mean power of the turbine,which is reduced by c. 15-20% for the waves considered. Mean thrust is also reduced but to a lesser extent. Blade thrust and power are observed to fluctuate with significant amplitude as the blades rotate (far more so than for the case of shear flow with no waves reported in D4). Blade thrust fluctuates by c. ±10-20% about its mean value, whilst blade power fluctuates by c. ±100-200% about its mean value, with blade torque (and thus power) reaching negative values through the rotation cycle depending on the relative phasing of the passing wave to the blade rotation.Surface waves are seen to accelerate the wake recovery process as might be expected due to the wave kinematics increasing the mixing between through-turbine and bypass flows