|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 report documents an investigation into the effect of ambient turbulence levels on the wakes of the two turbine types considered previously: a ‘conventional’ low-solidity turbine and an opencentre high-solidity turbine. In this sense, it can be considered an extension of the work of Deliverables 1 and 2. A further part of the scope of the present deliverable is to consider the necessity of updatingthe end-of-near-wake parameterization developed in Deliverable 3 to account for the effect of the ambient turbulence.
Five different intensity/length-scale combinations were investigated. For the low-solidity turbine, each of these combinations were run for five different combinations of the tip speed ratio and domain radius (i.e. domain blockage) to give a total of 25 simulations.
Two straightforward conclusions may be offered from the present set of results:
- First, variation in the levels of ambient turbulence has little effect on the power and thrust coefficient, and a minimal effect also on the velocity profiles in the immediate wake.
- Second, the differences that are observed in the wake velocity profiles with varying levels ofthe ambient turbulence intensity occur further downstream, and become more significant progressing downstream before beginning to fade out. Such differences should be accounted for by a far-wake model which is sensitive to turbulence, as is indeed the case with GL Garrad Hassan’s existing WindFarmer software