| The study of wake characteristics of wind turbine is of great significance to the micro-location,load forecasting,power prediction and control strategy of wind farms.However,the traditional numerical calculation of wake and wind tunnel experiments cannot accurately describe the wake characteristics under natural conditions.Therefore,a 33 k W wind turbine with two blades is tested and numerically simulated under the neutral atmospheric boundary condition.The velocity and turbulence characteristics of the wake are obtained.The asymmetry characteristic of the wake in the experimental and numerical calculations are analyzed.In addition to,under different inflow velocities,the characteristic of the wake in the neutral atmospheric boundary layer is studied.The main working contents are as follows.(1)Study of wake characteristics of wind turbine is carried out under outfield test conditions.The inflow and wake of the test unit and the operating parameters of the wind turbine are measured using the outfield test platform.The velocity defect,turbulent kinetic energy and probability distribution of flow angle of wake measuring points are analyzed,and the spectral characteristics of turbulent coherent structure in three directions are analyzed.The axial velocity defect rate of three measuring points is obtained between 32.18% and 63.22%.The horizontal flow angle and the vertical flow angle show different distribution law.The power spectrum of the vertical fluctuating velocity shows the rule of slope-1,and that of the horizontal and axial fluctuating velocity are all presented with the slope-1 and-5/3 rules respectively.By comparing the correlations of flow between the left?right and intermediate measuring points,the left and right measuring points show obvious asymmetry,and the reason of asymmetry is explained.(2)Numerical simulation study is carried out under experimental conditions.The pilot unit in the neutral atmospheric boundary layer is simulated by the method about large eddy simulation model and braking line model.The accuracy of numerical simulation is verified by comparing with the experimental results.Furthermore,the asymmetry of the wake under the action of lateral force is further proved.The speed of wake has been restored to the 90% of inflow at 6D after wind wheel,and to the inflow state at 10 D.The wake velocity distribution curve of wind turbine is M-shaped.After the inflow through the wind wheel,the axial inertial subrange of the turbulent coherent structure becomes wider and the dissipation region moves to a higher frequency position.(3)By comparing the velocity defect,wake boundary,turbulent kinetic energy and vorticity of wake of wind wheel of the test unit under different inflow velocities,and the probability distributions and spectral characteristics of low-speed axial torque,the wake and torque characteristics are acquired under different inflow velocities in the neutral atmospheric boundary layer.The turbulent kinetic energy is greater in the neutral atmospheric boundary layer with high wind speed,which is beneficial to the recovery of the wake.when the average wind velocity is 4m/s,the wake boundary is clear and the tip vortex is obvious.However,when the average wind velocity is 9m/s,the wake boundary becomes blurred and the blade root vortex and leaf tip vortex are not obvious.The speed defect has no obvious shape after the wind wheel 2d.The turbulent kinetic energy and velocity distributions in the vertical and horizontal directions of the wake are obviously asymmetric.Comparison with stable inflow condition,the variation range of the low-speed in the neutral atmospheric boundary layer is wider,which is accords with the Weibull distribution.The difference of their spectral characteristics mainly exists in the corresponding position of low-frequency and frequency peaks,which indicates that the turbulence response of wind turbines to the atmospheric boundary layer is obvious. |
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