Research On The Model Of Streamwise Turbulence Intensity For Wind-turbine Wakes

Accurate prediction of the streamwise turbulence intensity in turbine wakes is of great significance to the layout of wind turbines.However,the understanding on the streamwise turbulence intensity in the turbine wakes is very inadequate,and we still lack an accurate model to predict the added turbulent intensity in the wakes.To address these issues,the wakes of a single turbine and single-row turbines are studied via large-eddy simulation under neutral atmospheric condition,and the evolution of the added streamwise turbulence intensity(ΔIu)in single turbine and single-row turbines wakes are deeply researched,then a novel three-dimensional analytical model and novel superposition method of ΔIu are proposed.The comparison with date shows that the newly-derived models are agreement well with simulations and experiences.The main research contents of this dissertation are as follows:(ⅰ)The wakes of a single turbine with different thrust coefficients and ground roughness heights are studied via large-eddy simulation,and the results of ΔIu in the wake are analyzed in detail,we find that the ΔIu’s peak position expands linearly andΔIu exhibits a self-similar characteristic.The numerical results show that ΔIu in the turbine wake presents an obvious double-peak characteristic in the horizonal plane at the hub height,due to the ground effect,the ΔIu above the hub height in the vertical plane is largest;And like the velocity deficit of the turbine wake,the ΔIu’s peak position expands approximately linearly along the downstream to both sides in the horizontal plane and to the up side in the vertical plane.The peak positions of the ΔIu appear near the locations with maximum wind shear,which agrees well with the half width of the wake.(ⅱ)A novel three-dimensional analytical model of ΔIu is proposed.Based on the above findings of ΔIu characteristic in the horizonal plane at the hub heigh,a physical model of the ΔIu is proposed considering the wake expansion which are often neglected by the previous models,a combination of the Gaussian function and cosine function is adopted to characterize the variation of ΔIu in the radical direction,and an asymmetrically two-dimensional model of ΔIu is derived.Considering the ground effect,a new three-dimensional correction model is proposed accounting for the ground effect,then,a novel three-dimensional analytical model of ΔIu is proposed.Data from both wind tunnel experiments and high-fidelity numerical simulations are adopted to validate the proposed model.The results show that the proposed model can accurately predict the variation of added streamwise turbulence intensity in both the vertical and horizontal directions,it also can accurately predict the wake expansion characteristics,and outperforms the existing models.(ⅲ)A novel superposition model of ΔIu is proposed.The wakes of a single-row six equidistant turbines with two different ground roughness heights are studied via large-eddy simulation,it reveals the basic characteristics of ΔIu first increase at different turbine positions and then tends to be stable in the case of full wake.Based on the recognition that ΔIu is more susceptible to the influence of adjacent turbines,the influence of different turbulence intensity superposition methods is studied,and a novel superposition model of ΔIu is proposed.Numerical simulation results show that the proposed model can accurately predict the streamwise turbulence intensity in the wake overlap area.The work in this paper has deepened the understanding of the evolution of streamwise turbulence intensity in wake.The proposed turbulence model and turbulence superposition model can provide guidance for the optimization of turbines arrangement.