Study On The Numerical Simulation Of Wind Turbine Wakes Effect

The distribution of wind velocity will be affected by many factors,such as calculation accuracy of the wind turbine wake model and stability of the atmospheric boundary layer,which thereby affect the assessment of total power generation for the wind farm.During the early stage of the wind farm construction,assessment for the total power generation is one of the most important criteria for micro-sitting,whose accuracy has a direct impact on the layout optimization of wind turbines.Interfering with each other for the wake between wind turbines will reduce the wind energy utilization efficiency of the wind farm,which directly affects the whole economic benefit of the wind farm.Therefore,an in-depth study of the wind turbine wake is of great significance.This paper has separately proposed two revised engineering wake models,i.e.,the Park-Polynomial Model and the Park-Gauss Model,mainly based on the hypothesis of the Park Model that the wake region is in linear expansion and the wind velocity is in polynomial and Gaussian distribution in the cross-velocity.The study on the wind turbine wake effect is based on these two newly revised engineering wake models and the Actuator Disk Model based on the open source software OpenFOAM,with the impact of atmospheric stability on wake effect has been taken into consideration as well.Thereafter,the study for the impact of atmospheric boundary layer stability on micro-sitting layout optimization of the wind farm is conducted based on newly revised engineering wake models.Details of the study are as follows:Firstly,carry out the study on the numerical simulation of single wind turbine wake.Two different numerical simulation methods are used for simulating single wind turbine wake.The first method is carrying out the study on the wind turbine wake through CFD based on the open source software OpenFOAM,adopting the Actuator Disk Model(ADM)and selecting the k-? SST Turbulence Model to conduct the numerical simulation for the wake flow of single wind turbine.The second one is carrying out the study on the numerical simulation for single wind turbine wake by two newly proposed engineering wake models,i.e.,the Park-Polynomial Model and the Park-Gauss Model.The results indicate that based on the open source software OpenFOAM,adopting the ADM+ k-? SST Turbulence Model could better simulate the wake flow of single wind turbine,and wind velocity recovery rate in near wake region is faster than several engineering models;two newly revised engineering models could also well simulate the wind velocity in wake region of single wind turbine;the Park-Gauss model with accuracy nearly close to test results is best in overall performance compared to several other engineering models,which is more consistent with the actual flow field in the velocity-cross distribution.Secondly,carry out the study on the numerical simulation of wake effect for multiple wind turbines.Main job of this part is to conduct the numerical simulation of full wake and partial wake for multiple wind turbines with two different methods.The first method is to conduct the numerical simulation of full wake and partial wake for two wind turbines through CFD method based on the open source software OpenFOAM and adopting the ADM+ k-? SST turbulence model.The second one is carrying out the numerical simulation of full wake and partial wake for two wind turbines by two newly revised engineering wake models,i.e.,the Park-Polynomial Model and the Park-Gauss Model.Thereafter,through a comparative analysis of calculated results with the Park Model,the 2D Jensen Model and LES Numerical Results,following conclusions could be drawn: ADM could better simulate the full wake and skewed wake effect of multiple wind turbines;newly revised Park-Gauss Model could better simulate the full wake effect and the wind velocity in wake region;as for the skewed wake effect simulation,both the Park-Gauss Model and the Park-Polynomial Model could better simulate the wake flow field,while the later is superior to the former;two newly revised engineering wake models not only have an accuracy nearly close to the LES result,but are more consistent with the actual flow field in the radial distribution.Thirdly,carry out the study on the numerical simulation of the impact of atmospheric boundary layer stability on wind turbine wake effect.Main job of this part is to consider the impact of atmospheric boundary layer with three different states on wind turbine wake effect,select the newly revised Park-Gauss Model to conduct the numerical simulation of the wake effect for single wind turbine and the full wake effect for multiple wind turbines,and adopt the newly revised Park-Polynomial Model to conduct the study on numerical simulation of skewed wake for multiple wind turbines.The results show that the more unstable the atmospheric boundary layer is,the faster the wake wind velocity of wind turbine will recover and the greater the expansion radius of wake is.That is to say,the wake wind velocity is of fastest recovery rate and maximum radius of the wake expansion when the atmospheric boundary layer is unstable,and in the second place when the atmospheric boundary layer is neutral and of slowest recovery rate and minimum radius of the wake expansion under stable atmospheric boundary layer.At last,carry out the study for the impact of atmospheric boundary layer stability on micro-sitting layout optimization of the wind farm.Main job of this part is to use the Niche Genetic Algorithm to conduct a study on layout optimization of wind turbines in the wind farm under two wind conditions(constant wind speed and speed & variable wind speed and direction)based on two newly revised models,i.e.,the Park-Polynomial Model and the Park-Gauss Model.The results show that the stability of the atmospheric boundary layer has a significant impact on micro-sitting layout optimization of the wind farm.The more unstable the atmospheric boundary layer is,the more the total number of units installed in the wind farm is,the higher the total power generation and the wind power utilization efficiency are,and the less the cost per kW is.