||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 ducted marine turbine. A full scale rotor is simulated using three-dimensional Computational Fluid Dynamics (Ansys Fluent) in which the rotor is embedded within a rotating sliding mesh within an outer stationary duct. The turbine is subjected to a sheared flow profile with surface wavesaligned with the current flow direction. 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. 20% for the waves considered, which is very similar to the power reduction for the bare turbine.
- Mean thrust is also reduced but to a lesser extent.
- Blade thrust and power are observed to fluctuate with significant amplitude as the blade rotates (far more so than for the case of shear flow with no waves reported in D4).
- Blade thrust fluctuates by c. ±10% about its mean value, whilst blade power fluctuates by c. ±100% about its mean value.
- These fluctuations are smaller than those for the bare axial flow turbine(by a factor of around two).
- The maximum blade torque fluctuation is around the same as the mean blade torque, such that the instantaneous torque is rarely negative, compared to the bare axial flow turbine, the blades of which experience long periods of negative power contribution.
- Thus the ducted turbine in sheared flow with waves delivers lower power yield but its blades experience substantially reduced fluctuating load