Hydrodynamic Performance of a Vertical-Axis Tidal Current Turbine in Surge Motion Using a 2-D Vortex Panel Model

Under real sea conditions, floating vertical-Axis tidal current turbines experience motions in six degrees of freedom which impact the hydrodynamic performance. In this paper, a 2D freewake vortex panel method (U2DiVA) is adopted as a time effective tool to assess the hydrodynamic response of an existing floating vertical-Axis tidal turbine under platform s surge motion in uniform tidal current. The results of the numerical simulations show that the surge motion modifies the flow field perceived at the blades, affecting the instantaneous value of the tip speed ratio and the time evolution of the induction field. Consequently, surge motion impacts on the structural strength of the turbine by introducing multiple frequencies of oscillation of the hydrodynamic coefficients and increasing the peak loading on the rotor. Surge motion is found to be beneficial to the average power extraction while only marginally affecting the mean loading. The preliminary findings of this research provide insights about critical aspects for the design and evaluation of floating vertical-Axis tidal turbine systems.