Numerical simulation of local climatic impact of an operating wind turbine

Abstract

Wind energy is commonly considered to be a clean and environmentally friendly renewable energy resource, as they do not pollute our atmosphere with greenhouse gas, nor do they cause any radioactive problems compared to nuclear energy. However, there are still some environmental impacts due to the installation and operation of the wind turbines that cannot be ignored, such as noise, visual and climatic impact. Especially, the observed local climate change in some wind farm areas has attracted general concern in recent years. Experts suspected that long time operation of wind turbines in an area can cause changes to local precipitation, evaporation of the water on earth surface, and even affect the frequency of drought happening. Nevertheless, we still cannot figure out whether these changes would be caused by wind turbines or not. The target of this study is to investigate the potential local impact of an operating wind turbine by numerical simulation. Because of the big geometric size of commercial wind turbines, experimental method is very limited in this type of study. Numerical simulation using CFD is considered to be a suitable approach and commercial software “FLUENT” is utilized in this study. Firstly, an accurate 3-D numerical wind turbine model was established and the frozen blade method was used to realize the rotation of the wind blades. Before further simulation, a wind-tunnel test has been undertaken by using a scaled physical wind turbine model for validation purpose. The experimental results show good agreement with those predicted by the numerical simulation. This suggested that the computation results were validated and the computational model can be used for further study. In this research, three wind turbine cases, with different typical ambient temperature and surface temperature, were simulated. Characters like wake structure, turbulence intensity and local temperature change was collected and analyzed in each simulated case. The results show that the operating wind turbine can bring obvious velocity deficit in the wake and a strong turbulence intensity enhancement was observed at the top tip because of the rotation. Also, local temperature change was found in the near wake region. The investigation of the local impact of the operating wind turbine is very significant. This study provides a valuable insight into the potential impacts of wind farms on local meteorology, which is rarely studied before. Meanwhile, a more comprehensive study on the effect of a wind farm on the environment is highly recommended.