Modelling a Tidal Turbine in Unsteady Flow

A brief review of the literature is provided on the characteristics of marine currents and the approaches used for simulating tidal turbines. The feasibility of using CFD models to simulate time-dependent turbulent flow around a tidal turbine is then explored. Two different approaches for specifying the structure of the turbulent inflow conditions in CFD models are compared: the von Krmn spectral approach and the Synthetic Eddy Method (SEM) of Jarrin et al. (2006). The former model is commonly employed in the wind industry and is coded into Garrad Hassans Tidal Bladed and NRELs TurbSim. Different approaches are also tested for decomposing the turbulence at the inlet into resolved and modelled components. The results from these tests indicate that the turbulence produced using the SEM inlet conditions is slightly less susceptible to decay with downstream distance than the von Krmn approach provided that the modelled turbulent kinetic energy accounts for only a small fraction of the total turbulence energy.