|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.
The aim of this deliverable is to demonstrate a working model of mesoscale tidal flows, and to provide a fully-validated approach for doing so, which can be utilised in WG3 WP2 D5b to model arrays of tidal turbines. In this report, the development, testing and validation of a mesoscale, three-dimensional tidal channel model is detailed. The modelling work used the computational fluid dynamics software Code Saturne,with unsteady Reynolds-averaged Navier-Stokes equations resolving the turbulent tidal flow. The simulations were large, fully parallel simulations, running on Eddie, the University of Edinburgh’s parallel computing resource.
A real tidal channel was chosen as a template for constructing the model –the Sound of Islay between the islands of Islay and Jura,off the West Coast of Scotland. This is an appropriate choice, given that it is due to be used as a test bed for a demonstration tidal turbine array. It possesses the qualities of a tidal site ideal for marine renewable energy generation.
Tests were conducted on the problem geometry, mesh resolution and turbulence profiles. The tests were mainly to address the often competing issues of accuracy versus computational resource, as more accurate simulations tend to require larger computers and more disc space. The results are used to determine an appropriate level of trade-off between the two.
Once this balance had been attained, simulations were run with the flow at different stages of a tidal cycle. An appraisal of the time-averaged downstream flow results was madet o ensure that the characteristics of velocity, turbulent kinetic energyand turbulent dissipation profiles persisted;t hese would represent the incoming flow to the turbines in D5b. Finally, a comparison was made with flow profiles from other models of the Sound of Islay and with actual ADCP measurements from the sound itself. Good agreement was found with both.