Numerical Research On Influence Of Wake Flow Of Wind Turbine Under Yaw

As a renewable and clean energy source,wind energy has been greatly favored by all countries in the world.However,due to the complex and changeable natural wind,the wind turbine runs in a complex random wind field,and it is always at a yaw condition.The yaw leads to a decrease in the wind energy utilization rate and changes in the wake flow field.Therefore,it is of great significance to analyze the variation of wake flow field of a wind turbine under yaw condition.In this paper,theoretical analysis and numerical simulation are used to explore the wake characteristics of a yaw wind turbine for the design of wind turbines and the layout of wind farm wind turbines.Taking the S-wing three-blade horizontal axis wind turbine with a rated power of 300 W and a diameter of 1.4m as the research object,the wake flow field of a horizontal-axis wind turbine under yaw state was numerically simulated based on the ANSYS CFX work platform.The qualitative and quantitative analysis of the wind speed,the different sharp speed ratio,the variation of the output power of the wind turbine under different yaw conditions,the evolution law of the wake velocity after the wind wheel,the deflection of the wake and the attenuation and recovery of the turbulence are also analyzed.The main research content of this article includes the following three aspects:Firstly,monitoring and analysis of the blade surface pressure and output power of wind turbines in different yaw states revealed that the pressure difference at the blade surface decreases with the increase of the yaw angle in the same radial section.At the same yaw angle,the closer to the blade tip in the leaf spanning direction,the greater the pressure difference between the blade pressure surface and the suction surface,revealing that the blade tip has the largest functional force.Under the rated condition,the output power decreases with the increase of the yaw angle,and the degree of reduction increases with the increase of the yaw angle.The critical value of the yaw angle for the output power of the wind turbine is 15 degrees.The output power of the wind turbine at the same yaw angle increases with the increase of the tip speed ratio,and the critical value of the yaw angle of the wind turbine output power is 15 degrees under the same sharp ratio.Secondly,after the wind wheel is deployed,the evolution process of the trail of the wind turbine and the deflection process of the wake are analyzed.Through the study,it is found that the yaw leads to the deflected side of the wind turbine wake and the wake center in the negative direction of the X axis,and the greater the deviation angle,the greater the skew of the wake.The larger the yaw angle is,the smaller the wake loss is,the faster the wake speed is recovered,and the yaw shortens the wake of the wind turbine.At the same axial position,the wake is asymmetric.The larger the yaw angle is,the bigger the degree of curvature of the wake is,the more chaotic the wake is.The wake velocity in the wake of the wake follows the smaller the yaw angle,the smaller the loss of the velocity,the lower tail velocity of the wake is more serious,and the difference of the wake velocity of each radial position is great.The wake angle increases with the increase of axial distance,and then decreases to 0 degrees.At the same axial position,the wake angle of the wake on the upper side is relatively small,and the wake angle of the wake is relatively large,and the maximum value is close to the yaw angle.Finally,explore the changes in turbulence intensity and wake vortex before and after wind turbines in different operating conditions.It is found that the turbulence intensity at the wake of the wind turbine increases with the increase of yaw angle,and the turbulence intensity is lower than the entry value after 0.4D.The attenuation of the intensity of the turbulence in the incoming flow of the wind turbine causes the turbulence intensity to be lower than the inlet value before the wind turbine after 0.4D,and the turbulence intensity attenuation in the six yaw conditions in front of the wind turbine is consistent.Under the same yaw conditions,the turbulent intensity attenuation calculated by the SST k-? model is the smallest,and the turbulence intensity increases first and then decreases as the wind speed increases.At the same axial position,the turbulent intensity nearer the tip of the wake along the leaf spanning direction is smaller and the turbulent intensity is decreased with the yaw angle increasing.The intensity of the turbulence at the lower side of the wake is larger than that at the upper side.When the wind turbine is in the yaw state,the wake vortex is asymmetrical,and the distribution of the vorticity distribution on the upper and lower side of the wake is not consistent.The larger the yaw angle the larger the vorticity value,the more irregular the overall shape of the wake vortex.