Effects Of Low-level Jet On Aerodynamic Performance Of Horizontal Axis Wind Turbine

Wind energy is one of the energy sources that can effectively mitigate energy shortage and environmental deterioration.Wind electricity is a form of scale application of wind energy.Inflows can affect the design and operation of wind turbines,and low-level jet(LLJ)is one of them.A 1.5MW three-blade horizontal axis wind turbine was investigated to explore effects of low-level jet on aerodynamic performance of horizontal axis wind turbine by numerical simulation and theoretical analysis.Firstly,power and thrust of the turbine under multiple wind speed was calculated to verify the efficiency of simulation.Based on it,aerodynamic performance of wind turbine under uniform flow,shear flow and low-level jet were compared: under the jet,larger than under uniform and shear flow are power and thrust of the rotor,surface pressure of the blade,normal force coefficient and tangential force coefficient of each section.Stall area of blade surface is larger than other two types of flow especially near the root,and the separation vortex phenomenon of sections under LLJ falloff is more obvious.Under LLJ,the diffusion of axial velocity is more obvious in the horizontal plane,and there is a low-speed zone at wake region above hub center in the vertical meridian plane.Under low-level jet,the change of blade thrust with azimuth angle presents double peak.Values of blade yaw moment and overturning moment are greater than wind shear.Normal force coefficient and tangential force coefficient of sections decreased gradually from root to tip,and shows two peaks under LLJ.Changes of aerodynamic forces and torques of the rotor are much more drastic,and fluctuations of rotor thrust and torque are more frequent.Secondly,effects of LLJ strength,one of three structural characteristics of LLJ,on aerodynamic performance of wind turbine were discussed: with the increase of LLJ strength,what increase are power and thrust of the rotor,surface pressure of each section,normal force and tangential force on unite length,stall area on the suction surface expands.Influence of LLJ strength on pressure coefficient is remarkable near blade root.The low-speed zone behind the blade above hub reduced,and tend to compress to rotation axis.Thrust of the blade increases.Blade yaw moment varies a lot at azimuth angle of 90o and 270o.Overturning moment has largest values near 0o and 180o,but the difference under each LLJ strength is small.Normal force coefficient and tangential coefficient of each section have significant differences near 90o and 270o,but a few differences at other azimuth angle.What increase with LLJ strength are values of rotor thrust and torque,rotor yaw moment and overturning torque,and the fluctuation becomes more intense.After that,effects of LLJ width were discussed: with the increase of LLJ width,what increases are power and thrust of the rotor,surface pressure of each section,normal force and tangential force on unite length,stall area on the suction surface expands.Influence of LLJ width on pressure coefficient is more notable near blade tip.High-speed area before leading edge increases and low-speed area behind trailing edge decreases,the low-speed zone decreases significantly.As LLJ width increases,blade thrust,yaw moment and overturning moment fluctuate gently,values of blade thrust and overturning moment raised.Fluctuation of normal force coefficient and tangential force coefficient of sections tend to be gentle.Rotor thrust and torque raise,and fluctuate more gently.Fluctuation of rotor yaw moment tend to be flat.Fluctuation range of rotor overturning moment increases,when LLJ width equal to 11.25 m,fluctuation increases.Finally,effects of LLJ height were discussed: on the condition that jet main region locate in the range of the rotor,rotor power and thrust under different jet heights have little difference.With the raise of LLJ height,stull area of suction surface of the blade expand,surface pressure,normal force coefficient and tangential force coefficient of sections that higher than the highest jet height in the blade above hub center increase.When jet height raise,distributions of axial velocity behind and in front of the blade are different.After LLJ height exceeds hub center,the low-speed zone behind the blade expand significantly.With the raise of LLJ height,maximum value of blade thrust and yaw moment moves.Blade overturning moment increases at 0o,and decreases at 180o.Section normal force coefficient and tangential force coefficient move near 90o and 270o.When LLJ height locate in hub center,fluctuation of rotor thrust and torque increase,the amplitude is less than others,and fluctuations of that LLJ height is higher or lower than hub center are staggered.The farther the LLJ height is from hub center,the smaller the peak value of rotor yaw moment is,and fluctuations of maximum and minimum rotor yaw moment increase.Rotor overturning moment moves to negative direction as LLJ height raises.