Improving the efficiency and the wake recovery rate of vertical-axis turbines using detached end-plates

Aiming to improve the performance of vertical-axis turbines, this work is devoted to the development of detached end-plates, i.e., stationary end-plates that are not in contact with the turbine blades. The motivation is that the use of traditional attached end-plates has already been proven to be rather ineffective to increase the power coefficient of vertical-axis turbines because of the resistive torque (additional drag) generated by these wingtip devices moving with the blades (Gosselin et al., 2016). In this study, DDES simulations are performed using an unconfined H-Darrieus turbine with and without detached end-plates. It is found that the power coefficient is significantly increased when properly designed detached end-plates are used while the overall turbine drag coefficient remains almost unchanged. In addition to an improved power coefficient, we show that the use of detached end-plates can also lead to a faster recovery of the mean streamwise velocity in the turbine wake. An analysis of the streamwise momentum transport mechanisms allows us to conclude that the dominant contribution to the velocity recovery remains related to the transport term involving the mean spanwise velocity, as Boudreau & Dumas (2017) showed it for a vertical-axis turbine without end-plate.