Wind tunnel study of wind turbine wake characteristics over two-dimensional hill considering the effects of terrain slope and turbine position

Wake interference between turbines in wind farms can lead to significant losses in the overall power output from farms. In this study, the wake characteristics of wind turbines at different positions on two-dimensional hills with different slopes were investigated using a systematic wind tunnel test, where the hub of wind turbine and hills have the same height of 250 mm and the rotor diameter is 400 mm. Firstly, a novel normalization method to fairly evaluate the wake velocity deficit of turbine at different potions over hills was proposed. The wake of wind turbine sited at a hilltop was found to be much more affected by the terrain compared to that of wind turbine located in front of or behind the hill. Subsequently, the effect of terrain on wind turbine wakes, including velocity deficit and added turbulence intensity, were systematically analyzed. The slope of the hill mainly affected the wind turbine wake in the leeward side. The wake flow became wider and the peak value of added turbulence intensity was larger when the turbine located at the hilltop of gentle hill. However, for the steep hill case, the wind turbine wakes recovered faster than that in flat and gentle hill case. Finally, the performance of three typical wake models of velocity deficit and two models of added turbulence intensity were evaluated by using the experimental data. When the turbine was located at the hilltop, the conventional wake models for turbine over flat terrain cannot be directly applicable to the steep hill case as well as the gentle hill case. The Ishihara-Qian model gave reasonable distributions for the added turbulence intensity, except that in the steep hilltop case. Results of this study can provide guidance for the micro-siting arrangement and control strategies of wind turbines in wind farms sited on complex terrain.