A 3D NESTED MODEL FOR ASSESSING THE IMPACTS OF TIDAL TURBINES

Tidal current energy resources have the ability to provide a sizable proportion of our future energy requirements. However, to date there have been relatively few deployments of commercial-scale tidal turbines and, as a result, field data relating to hydro-environmental impacts is severely lacking. It is therefore necessary, to utilise numerical models to determine the likely impacts of deployments of turbine arrays on the surrounding environment. For the purposes of this research, an existing three-dimensional (3D) model was modified to incorporate the mechanics of energy extraction by tidal turbines. The tidal turbines are modelled as porous discs and energy extraction is simulated by incorporating the turbine thrust as a retarding force. To show how the developments to the model have improved its ability to simulate the characteristics of a turbine's wake it was compared to a two-dimensional (2D) nested model, a single grid 3D model, a single grid 2D model and to published experimental results. It is shown that the model is capable of simulating the far-field effects of turbine energy extraction. It is also shown that the nested 2D and 3D models produced results with higher values of correlation to experimental results than the corresponding single grid model results. The 3D nested model is able to simulate the effects of energy extraction on the velocity depth profile. These effects can only be observed using a 3D model, thereby demonstrating the benefits of utilising 3D over 2D models.