Fast power output prediction for a single row of ducted cross-flow water turbines using a BEM-RANS approach

A numerical model is proposed to efficiently compute the power produced by a row of Vertical Axis Water Turbines (VAWTs) deployed in parallel for various water flow conditions. As the computational cost of the unsteady Reynolds Averaged Navier Stokes (URANS) approach is high, a coupled Blade Element Momentum (BEM)/Reynolds Averaged Navier-Stokes (RANS) approach is developed, restricted to a 2D approximation. The HARVEST hydrokinetic devices considered in this study are made of twin contra-rotating VAWTs of ducted H -Darrieus type rotors. Momentum source terms are derived for such rotors from URANS simulations taking into account the presence of fairings and also incorporating the optimal tip speed ratio (TSR), thanks to a procedure based on local flow conditions upstream of the rotor path and on the mass flow through each rotor.