Characterisation of Wave-Tidal Current-Turbulence Interactions at Tidal Energy Sites in the Orkney Islands

Results obtained from numerical modelling of wave and tidal currents and the resulting turbulence parameters at tidal energy sites in the Fall of Warness, which is a region consented by the Crown Estate for deployment of tidal stream devices in the Orkney Islands, Scotland, are reported in this paper. The software suite MIKE 21/3, which is a coupled wave-tidal flow model, has been used for this purpose. The coupled wave-current model is driven by boundary inputs of spatially and temporally varying wind, wave and tidal elevations. Turbulence closure is achieved using a two-equation (k-ε) turbulence model. The coupled model has been calibrated and validated with field measurements of waves and tidal currents acquired by Acoustic Doppler and Current Profilers (ADCPs) deployed in the Fall of Warness. The results indicate that the coupled model works well and the predicted wave-current parameters provide very good match to site measurements at different depths of the water column. The model outputs such as significant wave height, peak wave period, mean wave direction, tidal current speed and its direction, Turbulent Kinetic Energy (TKE) and its dissipation rate and Eddy viscosities are presented and discussed. These parameters will find its use in the design of tidal turbine components and its supporting structures.