Numerical Simulation Of Wind Farm Flow And Operation Characteristics Based On Multi-scale Coupling Model

With the increasing attention to environmental issues worldwide,as a clean and renewable energy source,wind energy plays an increasingly important role in the world's energy structure.At present,in the context of the cost of wind power generation is still higher than that of thermal power,improving the economics of wind power generation is an important basis for ensuring the sustainable development of the wind energy industry.Since the cost of wind power generation largely depends on the wind resources of the wind farm,the key to improving the economic efficiency of wind power generation lies in the scientific location of wind farms and the layout optimization of wind turbines,which depends on the accurate assessment of wind resources and a better understanding of the wake interference effect in the wind farm.The assessment of wind resources should be carried out through the mesoscale meteorological model,and the study of wind farm wake interference needs to be conducted under the framework of microscale computational fluid dynamics(CFD)method.Therefore,the research of wind farm simulation with microscale and mesoscale coupling mode is of great significance for the scientific location of wind farms and the optimal layout of wind turbines.In this paper,a multi-scale computing platform for the simulation of the flow field and operation characteristics of wind farms is established through the combination of computational fluid dynamics and mesoscale meteorological models.On the basis of the microscale CFD software OpenFOAM,the wind turbine flow field solver based on the large eddy simulation(LES)and the actuator line model(ALM)is developed,and the generator torque control and pitch control methods of the wind turbine are coupled to the solver,and a wind farm CFD simulation platform suitable for flat terrain and complex terrain has been established.On the basis of mesoscale Weather Research and Forecasting(WRF)software,through parameteric modeling of the interaction mechanism between wind farm and atmospheric boundary layer,a mesoscale wind farm parameterized(WFP)coupling model WFP-WRF is developed.In addition,a multi-scale WRF-CFD computing platform is developed by coupling the above mesoscale models with microscale models.Based on the above simulation platform,this paper has conducted a systematic study of the flow field and operation characteristics of the wind farm.Firstly,under the microscale CFD mode,the large eddy simulation platform coupled with wind turbine control strategies is used to study the performance of the wind turbine and the wake interference characteristics under dynamic inflow conditions,as well as the influence of wind turbine arrangement on the operation of wind farm.The operation response characteristics of the wind turbine under dynamic inflow wind speed conditions are explored,the results show that after coupling the newly developed control model,the rotor speed,torque,and output power of the wind turbine can respond well to changes in the inflow wind speed,and the simulated wind power curve of the wind turbine also agrees well with the actual power curve of the wind turbine.The research on the wake interference characteristics under dynamic inflow condition shows that,under the influence of wake,the fluctuation amplitude of the torque and axial thrust increases for the downstream wind turbines.With the increase of downstream turbulence,after the wind speed exceeds the rated wind speed,the pitch adjustment of the downstream wind turbine will have an "overshoot" phenomenon,which will cause the wind turbine output power to fluctuate slightly near the rated value.The simulation results under different layout schemes of wind farms show that the staggered arrangement has obvious advantages in reducing wind turbine load fluctuations and improving the capacity factor and the efficiency of the wind farm compared to other arrangement schemes,and increasing the streamwise spacing also helps to improve the capacity factor of the wind farm.Secondly,under the mesoscale mode,based on the WFP-WRF model,the flow field,real time power output characteristics in a real onshore wind farm,and the interaction of wind farm and atmospheric boundary layer are studied in the high resolution numerical simulation for the first time.The calculation accuracy of the model is verified using the measurement data and actual power output data of the wind farm,the results show that the current calculation model has high accuracy in the simulation of wind speed,wind direction and power output of the wind turbine.Next,the output power of each wind turbine in the wind farm and the operation efficiency of the wind farm are compared and analyzed under different wind directions,and the wind farm power output characteristics of the three main wind directions are quantitatively compared.In addition,the influence of wind farm operation on the wind speed and temperature of the atmospheric boundary layer is analyzed,the velocity and temperature fluctuation characteristics of different height levels under the influence of the wind farm are compared,and the influence of wind farm on the wind speed at different locations downstream of the wind farrm is quantitatively revealed.Finally,under the WRF-CFD model coupled with mesoscale and microscale,the multi-scale simulations of the flow field and operation characteristics of an onshore wind farm under complex terrain are carried out.The accuracy of wind power output results based on the mesoscale WFP-WRF model and the multi-scale WRF-CFD model is tested on the basis of the wind farm operation data,the results show that compared to the mesoscale WFP-WRF model,the WRF-CFD multi-scale model has obvious advantages in capturing the flow details and improving the simulation precision of the wind farm.Then,this paper considers the three conditions of the wind turbine on the upwind of the slope,the top of the slope and the downwind of the slope,respectively,and explores the influence of the terrain on the flow field around the wind turbine and the operation characteristics of the wind turbine.In addition,the influence of the inflow wind speed on the operation characteristics of the wind farm is also studied,and the evolution characteristics of the output power,axial thrust and rotor speed of the wind turbine are discussed under four different inflow conditions.The research in this paper has developed a multi-scale coupled calculation platform for the simulation of the flow and operation characteristics of wind farms.It can be used to assist the macro-siting and micro-siting of wind farms and has important engineering application value.