| At the Beijing International Wind Energy Conference in October 2020,representatives from more than 400 companies around the world jointly released the Beijing Declaration on Wind Energy,proposing that China’s total installed wind power capacity will reach at least 800 million kilowatts by 2030 and at least 3 billion kilowatts by 2060,providing more than 30% of the country’s electricity demand.At the same time,the "double carbon" goal for wind power development has put forward higher requirements.In order to accomplish the established goals and reduce the cost of wind energy,one of the common means of the wind power industry is to design larger,more efficient wind turbines.The downstream wake effect of larger wind turbines has a significant impact on the efficiency and safety of wind farm operations.In order to reduce the effect of wind turbine wake effect and improve the overall output of wind farms,this paper focuses on the effect of atmospheric stability on the wake of a single wind turbine,and the effect of atmospheric stability on the power generation efficiency and stability of aligned wind farms and vertically staggered wind farms.The study provides a basis for simulation and physical modeling of the interaction between flow fields and wind turbines under different stability conditions that affect their wake recovery and thus downstream wind farm power generation.The main research content and results of this paper are as follows:In order to understand the influence of atmospheric stability on the velocity distribution and structural evolution of wind turbine wake,the flow field characteristics of a single wind turbine under different atmospheric stability are studied by Large Eddy Simulation(LES),and the flow field structure is analyzed by Proper Orthogonal Decomposition(POD)method.The results show that atmospheric stability has a significant effect on the mean statistical characteristics and transient oscillation of the wind turbine wake,and the mean wake lengths of the wind turbine under convective,neutral and stable atmospheric conditions are around,and,respectively;the strongest wake meander and the largest wake center offset under convective conditions,and the offset increases with the increase of wake length;the transient wake offset at the downstream of the wind turbine under convective conditions can reach The instantaneous offset of the wake downstream of the wind turbine under convective conditions can reach 27.80%,while it is 18.75% and 8.75% under neutral and steady conditions,respectively.In addition,atmospheric stability also has a significant effect on the large-scale structure of the wind farm,with the scale of the downflow coherent structure being 5 and 1.67 times higher under convective and neutral conditions,respectively,than under stable atmospheric conditions,and the vortex energy content in the near-trail region is also significantly higher than under stable atmospheric conditions.A large eddy simulation method based on the brake disc model was used to investigate the effect of atmospheric stability on the magnitude and fluctuation of power generation,as well as the wake velocity and turbulence intensity of wind turbines at different locations in an aligned large wind farm with different atmospheric stability.The results show that the time-averaged dimensionless power output of the wind farm under convective,neutral and steady conditions are 76.45%,53.70% and 61.73%,respectively,and the convective and steady conditions significantly increase the overall power generation of the wind farm by 22.75% and 8.03%,respectively,compared to the neutral condition.The(Relative standard deviation,RSD)RSDs of wind farm power fluctuations for the three weather conditions were 14%,13% and 24%,respectively.The wind turbine wake lengths were 2.8D,4.5D and 5.3D,and the wake widths were 3.4D,2.4D and 1.8D under convective,neutral and steady conditions,respectively,and the wind turbine wake losses reached stability at row 5,row 8 and row10 or more,respectively;meanwhile,the turbulence intensity in the atmospheric boundary layer showed a trend of convective > neutral > steady,while the additional turbulence intensity was maximum in the steady atmospheric boundary layer and minimum in the convective atmospheric boundary layer and the smallest in the convective atmospheric boundary layer.Atmospheric stability affects the wind turbine wake velocity recovery and wind energy absorption and utilization by affecting the turbulence intensity of the incoming flow,which in turn affects the output power of the entire wind farm.The effects of four wind farm layout methods(VS0,VS1,VS3,LS1)with different atmospheric stability conditions on the output power of the whole wind farm were studied.The results show that the odd-high and even-low layout can effectively reduce the overlap of the front wind turbines on the wind turbine surface of the back wind turbines,reduce wake interference,and increase the total power output of the wind turbines;in particular,the vertical staggered layout of the wind farm under convective conditions can significantly increase the power output of the wind farm,with a maximum increase of 29.6% for the VS3 case.However,by weighting the impact of different wind turbine rows on wind farm power under three atmospheric stability conditions,it is found that horizontal staggered rows boost power by about 35.39%,and vertical staggered rows boost power by 5.69% and 24.78% in and respectively.At the same time,atmospheric stability will also have an impact on the power fluctuation of wind turbines,with a greater impact on power in the middle of the wind farm than in the entrance and exit areas of the wind farm.The vertical staggered layout only reduces the power fluctuation of the wind farm under stable atmospheric conditions,while increasing the power fluctuation of the wind farm under the same atmospheric stability conditions aggravates the power fluctuation of the wind farm,while the horizontal staggered layout both significantly reduces the power fluctuation of the wind farm.In addition,the additional turbulence intensity of wind farms varies under different stability conditions,with the highest additional turbulence intensity of 39%,41% and 76% for wind farms under convective,neutral and steady conditions,respectively.The additional turbulence intensity can enhance the interaction between the wind turbine wake and the surrounding fluid,increase the wind turbine plane energy density,and enhance the wind turbine power.Under unstable conditions,vertical staggered layout of wind turbines is more likely to induce additional turbulence intensity,but the effect is not significant;under neutral and stable conditions,horizontal staggering is more likely to induce additional turbulence intensity,and the effect is almost the same for aligned and vertically staggered wind farms. |
PDF Full Text Request