Wake Modelling behind a Vertical-axis Tidal-current Rotor

A group of close-packed contra-rotating vertical-axis rotors has previously been designed by Stephen Salter to maximize the fraction of flow passage swept (Salter and Taylor, 2006, IMechE). We model a single vertical-axis turbine (VAT) using actuator line theory to capture important flow features contributing to the fast wake recovery behind one of the rotors (Bachant, 2016, Wind Energy). Tip-loss effects and dynamic stall are investigated and incorporated in the model as corrections applied to the force terms in the actuator line method. The spoked-ring wheel is a more efficient load-bearing structure than a tower, which experiences drag and suppresses tip vortices caused by adjacent foils at different angles. Proper pitch control could solve the problem of dynamic stall. The Wind and Tidal Turbine Embedded Simulator (WATTES) (Creech et al., 2015, Surveys in Geophysics) is used to predict the dynamic response to the flow, where lift and drag force components are calculated from tabular aerofoil data. Using this approach, we examine the vorticity magnitude distribution in order to investigate the effect of wake turbulence on VAT device performance.