|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 involves the development of a parameterization for the fluid velocity field in the ‘end-of-near-wake’ region of a tidal current turbine wake. The parameterization links the wake velocity profile to the thrust coefficient and blockage ratio of the turbine.
Separate but related parameterizations were developed for the ‘conventional’ low-solidity turbine of Deliverable 1and the open-centre high-solidity turbine of Deliverable 2. Following this review of the literature, a new parameterization was developed based on an actuator disc blockage model, an empirical Gaussian wake velocity profile, and conservation of momentum principles.
The parameterizations for the two turbines differ in the empirical velocity profile, but are otherwise based on the same fluid dynamic principles. Comparisons were made between the new parameterizations and the CFD resultsof Deliverables 1 and 2, for the two turbine geometries.
A comparison was also made between the new parameterization and that used in the Wind-Farmer software, for the case of the low-solidity turbine.