Experimental characterisation of the wake behind paired vertical-axis wind turbines

Two vertical-axis wind turbines (VAWTs) benefit from a power increase when placed side by side in close proximity. To study the potential of paired VAWTs for integration in wind farms, wind tunnel wake measurements of lift-driven VAWTs are compared for isolated and three counter-rotating configurations. Because the wake of an isolated VAWT is deflected, the direction of rotation significantly influences the wake of paired VAWTs. The wake of counter-rotating VAWTs where the adjacent blades move downwind, exhibits a similar length, width and replenishment as the wake of an isolated VAWT. The wake of counter-rotating VAWTs with adjacent upwind moving blades, however, significantly differs from an isolated VAWT wake. While its wake length is similar to an isolated VAWT wake, its width and replenishment are not. Because of appealing wake characteristics, paired VAWTs exhibit unique advantages for wind farm applications, and especially for offshore floating wind farms

Influence of the direction of rotation on the wake characteristics of closely spaced counter-rotating vertical-axis wind turbines

Closely spaced counter-rotating vertical-axis wind turbines (VAWTs) exhibit a considerable power improvement compared to the same turbines in isolation. It thus makes sense to study their potential for wind farm production optimisation. With this objective in mind, the wake of an isolated VAWT is compared experimentally to the wake of counter-rotating VAWTs. Because of the unsteady aerodynamics, the wake of an isolated VAWT deflects towards the region behind its upwind moving blade. The direction of rotation thus directly influences the deflection of the wake. For paired configurations, it is possible to use this wake deflection as an advantage. A pair of counter-rotating VAWTs where the upwind moving blades are at the centre of the pair, exhibits a particularly narrow wake. With the benefit of a power improvement and a narrow wake, closely spaced counter-rotating VAWTs exhibit promising characteristics to improve the power density in a wind farm