Numerical Research On Wake Interaction Among Multiple Wind Turbines

Due to climate change,increasing energy demand and shortage of fossil energy,clean and renewable wind energy has attracted more attention than ever before.In the large wind farms,most wind turbines operate tightly clustered in arrays,as the economic constraints make it impossible locate the turbines adequately apart to prevent them from interacting with each other.The wake generated by the upstream wind turbines will affect the operation conditions of the downstream wind turbines in the array,which is called the wake effect.The most obvious influence of wake interaction in arrays are the velocity deficit and the increased turbulence causing higher loads on turbines downstream in an array,which will naturally causes a reduction in the power output for downstream turbines.Therefore,it is beneficial for the whole wind farm to reduce the wake interaction among wind turbines by reasonable restraining strategies.Offset arrangement of wind turbines,yaw and pitch angle control can effectively restrain the wake interference.Therefore,the detailed study of multiple wind turbines wake interference restraining strategies is helpful to control the wake of upstream wind turbines,and provide reliable help for the research of wind farm wake interference and the optimization of the overall power output of wind farm.In this thesis,the wake development of wind farm is simulated by using the fixed wind farm solver FXWF-SJTU developed independently by the laboratory.The effects of yaw and pitch angle on aerodynamic power output and wake interference among wind turbines are studied in detail.First of all,FXWF-SJTU solver is used to simulate the wake interaction between two offset wind turbines.By changing the rotational speed of the downstream wind turbine to change the tip speed ratio,the numerical simulations of the downstream wind turbine under 3 different tip speed ratios are conducted.The results obtained from the present simulations are compared to the data from the experiment “Blind Test 3” and other simulation models.Secondly,the wind farm which contains two tandem wind turbines when the upstream wind turbine is operated in different yaw or pitch conditions are simulated in detail.According to the analysis of power outputs,wake characteristics,and vortex structures,when the upstream wind turbine is operating in the different yaw or pitch conditions,the behavior of the wake and the inlet condition of the downstream wind turbine will be affected to a great extent.And the changing wake will also have a significant influence on the aerodynamic power output of the downstream wind turbine and the whole flow field around the wind farm.Finally,based on the numerical simulation analysis of upstream wind turbine in different yaw or pitch condition,the numerical simulation of the Lillgrund wind farm with 48 wind turbines is carried out.By changing the yaw angle or pitch angle of the first row of wind turbines in Lillgrund wind farm,the aerodynamic loads of each wind turbine in the wind farm are analyzed in detail,and the serious wind velocity reduction and turbulence intensity increase caused by the wake interaction among large wind farms are discussed.