Research On Improvement Of Semi-empirical Wake Model For Wind Turbine

Wind turbine wakes lead to velocity deficit and turbulence intensity increase in the downstream area of wind turbines.It results in power losses and fatigue load,which has negative impact on the economic benefits of wind farms.The semi-empirical wake model is often used to measure the wake effect,however,the accuracy and applicability of the currently used semi-empirical wake model are still to be improved.Therefore,an improved method of semi-empirical wake model based on high accuracy numerical simulation is proposed.The method has sufficient data support in wake area,and can save the high cost of wind tunnel testing.Firstly,three-dimensional full-scale multiblock structured mesh model was established based on NREL Phase VI wind turbine,including the nacelle and tower.Steady and unsteady numerical simulations were carried out,and the distributions of wind speed and turbulence intensity in wake area were studied.Finally,taking Jensen model as an example,the semi-empirical wake model was improved and the improved model was validated based on the rules.Main contents and conclusions are:(1)Wind turbine wake numerical simulations were carried out,and the detailed flow information of the wake was obtained.Three-dimensional full-scale multi-block structured mesh model was established including the nacelle and tower.RANS and URANS numerical simulations were carried out,and the CFD results were validated by comparing with the LES data.The simulation results accurately reflect the wind velocity distribution in the wake area,and can provide the data basis for semi-empirical wake model improvement.(2)The semi-empirical wake model was improved based on the numerical simulation results of wind turbine wake.Jensen model was improved based on the data of wind speed and turbulence intensity in wake.Based on the mass conservation equation,the parabolic function was used to describe the variation of wind speed along the radial direction.The wake decay coefficient was modified,considering the influence of environmental turbulence intensity and additional turbulence intensity.The Improved Parabolic Jensen wake model was obtained and the calculation accuracy was improved comparing with Jensen model.(3)The Li DAR measurement experiment of a single turbine wake was carried out to verify the accuracy and applicability of the modified semi-empirical wake model.The improved semi-empirical wake model was validated based on the wind velocity data obtained from the Li DAR measurement in wind farm,the ECN wind tunnel test data,and Sexbierum wind farm test data in the literature.The accuracy and applicability of Improved Parabolic Jensen model were verified,comparing with Larsen wake model.The feasibility of the improved method of semi-empirical wake model based on high accuracy numerical simulation was proved.