Influences Of Inflows On Power And Wake Of Large Scale Wind Turbine In Tibet Plateau In Winter

With its irreplaceable advantages,wind energy has become one of the most important clean energy.With the widespread investment of wind farms in high altitude,low temperature,and low wind speed regions.The wind turbines have complex and harsh operating conditions,which are well worth exploring.In order to deeply understand the operating conditions and state of large-scale wind turbines in low-temperature and high-altitude wind plant,the experiment method was mainly used in this subject.The inflows and wakes of a 3.6MW large scale horizontal axis wind turbine in a wind farm were measured by lidar simultaneously and recorded in the wind turbine data acquisition and monitoring and control system(SCADA)to study the inflows on the wind turbine output power and wake.In addition,today’s numerical simulation is widely used for its economy and convenience.Accurate simulation can remedy many shortcomings of experimental measurement,but its accuracy in reappearing external wind fields is still worthy discussion.Therefore,based on the field data measured by experiments,this project verifies whether the large eddy simulation can accurately reproduce the incoming,power and wake of a large wind turbine in the plateau outfield.In this thesis,we design the field experimental program firstly,then explain the wind measurement principle of lidar and the wind velocity inversion method,and then verify the accuracy of the experimental data and perform subsequent processing to lay the foundation for an accurate analysis below.Finally,the influence of inflows on wind turbine power and wake is studied,and the accuracy of numerical simulation is discussed.The main contents can be summarized as follows:(1)Analysis of stable operation of lidar and accuracy of measurement data and data processing.The data stream and the spatial detection position analysis of the laser emitted by the lidar can ensure the stable operation of lidar and provide guarantee for the accurate measurement of the experimental data.Through the regression analysis of inflows measured by the nacelle anemometer and nacelle lidar recorded simultaneously by SCADA system,the results are highly correlated.The sources of measurement indeterminate related to lidar hardware and meteorology in the experiment are discussed,and the uncertainty of different incoming wind speeds measured by nacelle lidar is calculated.The analysis of temperature,wind speed,wind direction,wind shear index,turbulence intensity,and SCADA recorded wind turbine output power based on the measuring data of the nacelle-lidar for the past month,the following rules are obtained:The large-scale terrain has a significant impact on the prevailing wind direction;when the wind speed is strong enough,the turbulence near the hub height obviously decreases with the increase of the wind speed;when the wind shear index is negative,it is mostly because of the wake region of the upstream wind turbines For the Gobi region of the plateau,the periodic temperature change caused by the diurnal alternation is obvious,and it will have a cyclical effect on wind shear(2)Influence of inflows on wind turbine output power and wakeBased on wavelet analysis theory,the analysis of wind speed data at different positions of incoming,power and wake under the same time shows that small-scale fluctuations of inflow will be filtered by the control effect of the generator,resulting in smoother output power;when the turbulent inflow that can cause large-scale fluctuations in the power of the wind turbine acts on the rotor,the frequency of power fluctuations is less than the frequency of wind speed,that is,the scale effect of turbulence will be amplified.The increase of incoming wind speed will increase the influence of high-frequency small-scale turbulent structures on wind turbines,and then increase the high-frequency fluctuations of power.The intermittent motion of incoming turbulence will have a significant effect on the height of the wake of the wind turbine;As the incoming wind speed increases,the cascade evolution phenomenon of the wake will be weaker,and the turbulence structure of the wake will be clearer.Based on the correlation function theory,autocorrelation and cross-correlation analysis of incoming wind speed and wind turbine output power and wind speed data at different locations downstream of the rotor in the corresponding period.It is show that under the same data length,the correlation coefficient between incoming and power tends to increase with the increase of wind speed;the influence is more obvious that inflows at the height of the hub on the part of the wake below the height of the hub,and the correlation between the wake and the inflow has a tendency to increase as the wind speed increases.Therefore,the strength of the wind speed fluctuations at different positions of the wake affected by the inflows not only depends on the spatial position relationship,but also the related to the incoming wind speed and the operation of wind turbineThe power spectrum characteristics of wind turbine output power based on SCADA data exhibited three distinctive regions,which are large-scale meteorological phenomenon affected region,turbulence characteristics and power fluctuation coupling region and affecting region of small-scale turbulent pulsation.In the affected regions,the power spectrum of the turbulence characteristic and the power fluctuation coupling region exhibits a slope of-2 and-5/3-4,and three peaks caused by the rotation of the rotor appear near the affecting region of small-scale turbulent pulsation.Two power-law relations of Φp/Φu～f-4/3 and Φp/Φu～f-4 appear respectively when the frequency is less or greater than 0.064Hz.(3)Large eddy simulation of wind turbine flow field characteristics under different inflows of field measurementBased on the OpenFOAM open source platform,a combination of devote line and large eddy simulation was used to simulate the wind turbine under experimental conditions.The results show that the error between wind speed simulation value and the experimental value is within 8.7%.The error between the numerical simulation results of the wind turbine output power and the experimental results is within 6%.Without considering the influence of nacelle and tower,the numerical results of the wake at one times diameter of rotor in the vertical direction are significantly different from the experimental results,and after 1.5 times the diameter of the rotor downstream,the wind speed in the vertical direction.The error range between the numerical simulation and the experimental results is within 10.09%.It can be seen that the numerical simulation of the velocity characteristics of the external field flow field has certain accuracy.