Performance and near-wake analysis of a vertical-axis hydrokinetic turbine under a turbulent inflow

This study investigates the performance and near-wake characteristics of a full-scale vertical-axis hydrokinetic turbine under a uniform inflow and turbulent inflow with a 5% and 10% turbulence intensity. The governing equations of the flow field are the incompressible Navier-Stokes equations expressed within an arbitrary Lagrangian-Eulerian framework to account for mesh motion. To discretize the system of equations, the residual based variational multiscale formulation, augmented with a weakly imposed Dirichlet boundary condition at no-slip surfaces, is used. Moreover, a turbulent inflow is prescribed using a synthetic turbulence generation method referred to as Smirnov's random flow generation and the near-wake characteristics are studied using a multi-domain method. While the performance of the turbine slightly reduced under a turbulent inflow compared to a uniform inflow, there was a negligible difference in its performance between the two turbulent inflow conditions. A turbulent inflow also resulted in large fluctuations of the instantaneous power coefficient which has important implications for the fatigue life of certain components. Lastly, the wake recovery was notably improved under a turbulent inflow suggesting that a shorter streamwise inter-device spacing may be acceptable in highly turbulent tidal sites.