Experimental Study of Turbulence Influence on Wind Turbine Performance

Regarding the issue about unmatched Reynolds number for downscaled wind turbine tests in wind tunnels, a study of the performance characteristics of a model wind turbine operating in the wake of another turbine of the same model under laminar and turbulent inflow was performed. The distance between the two turbines was set at 5, 10, and 15 turbine diameters. In the laminar inflow case, due to the low recovery rate in the wake of the front turbine, the efficiency of the rare turbine has been greatly reduced even when the distance was 15 diameters. To address this issue, turbulent inflow was created using an active grid system installed between the contraction and test-section of the wind tunnel; the maximum turbulence intensity can reach 20%. Velocity fields upstream and in the wake of the turbine were measured using a 2D-PIV system; 1000 pairs of images were acquired for each location to achieve statistical convergence. It was found that by using turbulent inflow the efficiency of both the upstream and the downstream turbine was highly improved. Also, it was found that the efficiency of both turbines is highly related to the turbulence intensity in the inflow. At a constant tip speed ratio for the upstream turbine of 10.3, and a distance of 5 diameters between them, the efficiency for the downstream turbine was 4.1 times higher than in laminar case; for 10 and 15 diameters with the same conditions it was 2.71, and 2.48 times higher respectively. The maximum efficiencies reached for the downstream turbine were 38.5%, 34.5%, and 24.6% for 15, 10, and 5 diameters of distance between respectively. Therefore, despite the low Reynolds number, a high efficiency close to the field was reached using turbulent flow created by an active grid system.