Study On Wake Characteristics For Horizontal Wind Turbine

With the increasing interests on energy issues,the trend of developing a green and clean energy is inevitable these days.The wind energy which is a popular clean energy has good prospects for its numerical advantages.With the increasing scale of wind farms,the increase number of wind turbines density cause problems,therefor the layout of wind turbines has become a research project that needs to be solved.To ensure the highest power generation efficiency,it is necessary to consider the influence of the wake generated by the upstream wind turbine on the downstream wind turbine.In order to achieve these goals,the researches on optimal layout of the wind turbine and the wake is necessary.This paper introduces the basic theory of wind turbine aerodynamics in the first section.Then solves the wake characteristics of wind turbines by computational fluid dynamics.It is difficult to simulate multiple wind turbines due to the complex structure of the wind turbine.In this paper,the pressure drop method combined with the CFD and brake disc models is used to reduce the pressure of the wind wheel when the airflow passes through the wind wheel,and then the effect of the wind wheel extracting energy is performed.Simulation of single-fan,dual-fan and single-row fans to analyze their wake characteristics.The specific research contents are as follows:(1)Introduce the pressure drop method and the turbulence model then simulate the model with single wind turbine.The obtained simulation results are compared with the measured data.The simulation results at 2.5D fit well with the actual measurements,but the speed is underestimated at 7.5D.The reason for the error is that the downstream flow energy of the SST κ-ω model is gradually attenuated and there is a wind turbine which is shut down between the measured wind turbine and the downstream 7.5D in practice.(2)Analysis of the pressure and velocity at the wake of the single wind turbine simulation results,it is concluded that the pressure and speed will be greatly reduced after passing through the wind wheel,and the speed is slower than the pressure recovery.By changing the flow velocity and thrust coefficient,it is concluded that as the wind speed increases,the speed loss is smaller,especially in the near wake region.(3)Simulate the series and staggered layout of the two-wind-turbine,analyze thepressure velocity changes,and the downstream is affected by the wake of the upstream fan when it is arranged in series.When the staggered arrangement,the influence of the wake of the upstream fan on the downstream fan is greatly reduced.(4)For the simulation of four single-row wind turbine,select 2D and 4D line spacing respectively.According to the analysis of the obtained simulation results,as the line spacing increases,the impact on the wind turbine is smaller,and the line spacing is basically unaffected when the line space is 4D.Two kinds of wind speeds are selected.The comparison results show that as the wind speed increases,the speed loss at the wake decreases,the wake width decreases,and the wake length increases.Analysis of the velocity distribution at the 7.5D area of the 2D wind wheel,the speed loss of the two wind turbines on the outer side is smaller than that of the inner two wind turbines.The reason is that the outer wind turbine is more integrated with the surrounding air environment than the inner wind turbine.The conclusions obtained in this paper can provide some reference for the optimal layout of wind turbines.