Simulating the Wake Downstream of a Horizontal Axis Tidal Turbine Using a Modified Vorticity Transport Model

To decrease the need for fossil fuels, the alternative energy resources must be not only economically viable but also sustainable in the long term. One of the most promising alternatives is the marine renewable energy resource. The relatively young marine energy industry is presented with two challenges: first, to deliver a continuous reliable power supply, and second, to minimize potentially harmful effects of the power extraction on the marine environment. The requirement to understand the interactions between a tidal turbine and the surrounding flow environment motivated this work. A tidal turbine mounted on the seabed induces a wake that extends far downstream of the device. As the direction of tidal flow changes, so does the position of the wake with respect to the device. The detailed study of the turbine wake has been conducted by means of computer simulations. An existing finite-volume computer model called the vorticity transport model has been modified to suit the purpose of simulating the wake of a horizontal axis tidal turbine subjected to a nonuniform flow typical of that close to the seabed. High-resolution computer simulations suggest that a progressive fragmentation of the vortical structure occurs during the development of the wake of a tidal turbine. The predicted fragmentation generates small-scale unsteady flow phenomena beyond five rotor diameters downstream of the device in the area previously thought unaffected by the presence of a tidal turbine. The effects of nonuniform flow on the vorticity structure downstream of a tidal turbine and the fragmentation process are analyzed in this work.