Numerical analysis of the performance of a three-bladed vertical-axis turbine with active pitch control using a coupled unsteady Reynolds-averaged Navier-Stokes and actuator line model

In this paper, we present a numerical model of a vertical-axis turbine (VAT) with active-pitch torque control. The model is based upon the Wind and Tidal Turbine Embedded Simulator (WATTES) and WATTES-V turbine realisations in conjunction with the actuator line method (ALM), and uses OpenFOAM to solve the unsteady Reynolds-averaged Navier-Stokes (URANS) equations with two-equation k - ε turbulence closure. Our novel pitch-controlled system is based on an even pressure drop across the entire rotor to mitigate against dynamic stall at low tip speed ratio. The numerical model is validated against experimental measurements and alternative numerical predictions of the hydrodynamic performance of a 1:6 scale UNH-RM2 hydrokinetic turbine. Simulations deploying the variable pitch mechanism exhibit improved turbine performance compared to measured data and fixed zero-pitch model predictions. Near-wake characteristics are investigated by examining the vorticity distribution near the turbine. The pitch-controlled system is demonstrated to theoretically decrease turbulence generated by turbine rotations, mitigate the intensity of vortex shedding and size of detached vortices, and significantly enhance the performance of a vertical-axis hydrokinetic turbine for rated tip-speed ratios.