Experimental investigation of the performance and wake effect of a small-scale wind turbine in a wind tunnel

Abstract

The wake of upstream wind turbines is known to affect the operation of downstream turbines and the efficiency of the wind farm. In this study, a systematic experimentation on performance and wake spatial evolution was carried out using a wind turbine model varying tip speed ratio, pitch and yaw angles. The change of pitch angle was observed to induce a greater effect on the wake velocity as compared to the tip speed ratio. This is interpreted in terms of “force viewpoint”, which describes more quantitatively the relationship between the turbine performance and the wake, as compared to the “power viewpoint”, based on the sole energy conversion. The turbine yaw angle is observed to cause not only a decrease in power and thrust, but also an offset and an asymmetry in the wake. The offset, quantified using the spatial distribution of the velocity minima, is modeled analytically. Comparisons of model estimations with the experimental measurements show that the proposed model can acceptably predict the wake offset of a yawed turbine. The observed dependencies of the mean velocity deficit and wake turbulence on power, thrust, and yaw angle, may suggest new derating strategies for wind farm optimization.