Effect of wall confinement on a wind turbine wake

Abstract

This study investigates the effect of wall confinement on a wind turbine wake as a means to guide future wind-tunnel-based wake studies. Large Eddy Simulation was utilised to simulate the wake region for two cases. The first case simulated the NREL phase VI wind turbine in a wind tunnel with 9% blockage. The reason behind selecting this case is the availability of the experimental data in the literature which enabled us in validating the model. The second case was the same turbine located in an unconfined environment, with the same flow upstream velocity. The results show that the wind tunnel walls significantly affect the wake development and its stability, even with a blockage of less than 10%. Tip vortices in the unconfined environment start to break down closer to the turbine compared to the wall-bounded case, resulting in a shorter wake recovery length for the unconfined flow. Vorticity contours reveal coherent vortical structures in the confined wake up to 20 turbine diameters downstream, while these structures dissipate after 16 diameters in an unconfined environment. The calculated power also showed that the turbine in the wind tunnel generates 5.5% more power than that in the unconfined flow. Collectively, these results provide an insight into the effect of walls on the turbine wake in both numerical and experimental studies, offering guidance on how wind tunnel studies relate to real, unconfined flows.