Effects Of Wind Velocity Fluctuation In Neutral Atmospheric Wind Farm On The Aerodynamic Characteristics Of The Horizontal Axis Wind Turbine

With the wind turbine in MW level is more and more widely used in the atmospheric boundary layer,the influence of turbulence on wind turbine is more and more serious.When considered the optimization of wind energy utilization,neutral atmospheric condition is the most in need of being studied.Therefore,this paper takes a 33 k W two-blade horizontal axis wind turbine as the main object to study the influence of wind velocity fluctuation on the aerodynamic load and tail vortex structure of the wind turbine.Firstly,based on the RANS theory,the correlative coefficient of turbulence and aerodynamic load of wind turbine was calculated in the paper.The results show that turbulence intensity is negatively correlated with the torque and thrust of wind turbine,and is positively correlated with yaw moment and overturning moment of wind turbine.Shear turbulence intensity leads to a reduction in wind turbine's thrust and torque,and a more obvious phase lag effect.Secondly,based on the improved Von Karman spectrum,the harmonic superposition method and the actuating line theory,an aerodynamic load analytical program in the condition of 3D dynamic flow is compiled and verified by comparing with the experiment and theoretical laws.To predict velocity field of wind turbine's far wake fastly and accurately,the nonlinear extension model for the boundary of far wake,the 2D Gaussian distribution model for the velocity deficit at different axial positions of far wake are used to model a program named 2D Nonlinear Gaussian Distribution Model(2D-NGDM).The accuracy of the model is verified by the Garrad Hassan's experiment and CFD.Thirdly,based on the program,the turbulence intensity,tip speed ratio,wind shear exponent are selected as the characteristic parameters of inflow,and the coefficient of power,torque,thrust,overturning moment and yaw moment are selected as the aerodynamic characteristic parameters of wind turbine.Through a L8(27)orthogonal test,the priority order of the influence of the flow characteristic parameters and their secondary interaction on the aerodynamic characteristics of the wind turbine is obtained.By the method of range analysis and significance analysis,we know that the coeffic ient of overturning moment and yaw moment is sensitive to the turbulence intensity.Then,for the target of quantitative analysis,based on path analysis theory,the direct path coefficients of the turbulence intensity,the tip speed ratio and the wind she ar exponent to the overturning moment are respectively 0.516,0.309,and 0.752;the direct path coefficients of the turbulence intensity and the wind shear exponent to the yaw moment are respectively 0.488,0.714.Finally,the correlation between the aerod ynamic performance of the wind turbine and the flow conditions under different turbulence intensity is studied.The results of power spectrum analysis show that when the inflow wind appears more intense fluctuating effect,the corresponding turbulent kinet ic energy and coherent turbulent kinetic energy can reach a high level and keep a long time,and the fluctuating horizontal flow angle and vertical flow angle reached their respective extremes,which causes the coefficient of torque,thrust,overturning mo ment and yaw moment appearing extreme and large fluctuations in the corresponding period.In the turbulent flow conditions,the spectrum peak positions of the coefficient of power,torque and thrust are even multiples of the rotation frequency of the wind turbine;the spectrum peak positions of the coefficient of overturning moment and yaw moment are odd multiples of the rotation frequency.When the turbulence level increases,the spectrum peak position of the aerodynamic characteristic parameters is basica lly constant,but the power spectral density and the peaks of the spectrum peak increase.When the turbulence intensity increases by a same size,the spectral density increases more at lower turbulence levels.Finally,based on the theory of LES and actuat or line model(ALM),the SOWFA program is compiled and debugged on the platform of Open FOAM.The results show that the difference between calculated values by Open FOAM and experimental data is less than 11%.The mean tip-vortex circulation captures ~86.74% of the blade-bound circulation,which is consistent with the results of other experiments and numerical simulations.Then,a numerical example is calculated according to the experimental conditions.The results show that the potential temperature is const ant along the vertical direction,which is exactly the characteristics of neutral ABL.The distribution of the average wind speed fits well with the law of the wall near the ground.The calculation spectrum of 3D fluctuating wind speed(u,v,w)on the measurement point in SOWFA agrees well with the improved Von Karman spectrum recommended by ESDU for neutral atmospheric condition.The recovery trend of the velocity in the far wake flow calculated by SOWFA agrees with GH model and the wake skew angle fit we ll with Coleman model.The difference between SOWFA and experimental data about inflow wind speed,power and thrust of the rotor is less than 7%,which meets the needs of engineering calculation.Frequent changes in the inflow wind direction may cause TKE and CTKE to increase,and have an impact on the power and thrust of a wind turbine.By the wavelet technique of the co-scalogram,we found that the low frequency vortex in the wind has a great influence on the aerodynamic characteristics of wind turbine.In a neutral atmospheric boundary layer,the mean tip-vortex circulation captures ~45.93% of the blade-bound circulation.Atmospheric turbulence causes mean tip-vortex circulation account for less of the blade-bound circulation,and exacerbates the dissipation movement of the tip vortex in the wake of a wind turbine.