Research On The Temporal-Spatial Inhomogeneity Characteristic Of The Wake Profile With The Proposed Temporal-spatial Wake Model And Wind Tunnel Experiment

Wake expansion of the upwind wind turbine closely influences the power output and fatigue load of downwind wind turbines.However,previous studies mainly focuses on the spatial distribution characteristics of the wake but ignore the time-varying characteristics of the wake profile,which highly affects the operation control strategy of the downwind wind turbine and increases the difficulty of achieving efficient and low fatigue load operation of the unit.In order to further understand the time-varying characteristics of the wake profile from the time change of the free incoming wind of the upwind turbine,a mathematic method for investigation on the temporal-Spatial inhomogeneity characteristic of the wake profile are given with the temporal wake model been proposed and its authenticity and accuracy is verified.Firstly,suitable typical near and far wake models are selected.Based on the relationship between the axial induction factor and the fan thrust coefficient,the necessity of correcting the axial induction factor was judged.Based on the anisotropy of wake expansion,the effect of turbulence intensity on the typical wake model is corrected to avoid repeated experiments and calculations of wake expansion coefficients.Secondly,the continuity of the modified typical near and far wake models was corrected using the super-Gaussian function to form a modified wake combination model.A more accurate wind velocity distribution in the flow direction behind the hub is obtained.Based on the time required for the incoming particle to flow from the wind wheel to a specific position downstream,the concept of delay time is proposed.The expression of the delay time is obtained by the modified combined model calculation.Combined with the engineering wake model,a temporal-spatial wake model that can describe the wind speed distribution over the whole field is obtained.Then,the experiment of the wake time variation characteristics of the wind turbine is carried out in the low-speed reflux wind tunnel with two experimental sections: Hot-wire anemometers are used to measure the wake velocity distribution of a single wind turbine.The wind speed distribution results of horizontal wake of hub center height under constant inflow are given: With the increase of axial distance,the wind speed of the wake fluctuates obviously in a certain range,but the variation tendency of loss of speed is generally Gaussian model.The prediction results of the modified combined wake model show that the modified combined model has a better prediction result for wake with higher turbulence intensity of free incoming.Under the same turbulence intensity of free flow,the combination of the near wake model and the far wake model based on the Gaussian distribution has a better prediction for the wake.The calculated value of the delay time is also influenced by the intensity of the flow turbulence.Finally,wind tunnel tests are carried out to verify the accuracy of the proposed temporal-spatial wake model with the relative error been analyzed.The prediction error of the temporal-spatial wake model is smaller than the prediction error of the wake model without considering the delay time.The prediction error of the Temporal-Jensen-Gaussian-k model gradually increases with the increase of the axial distance.Regardless of the time variation characteristics of the incoming flow,the error of the Temporal-Jensen-Gaussian-k model is almost within 4%.The results show that the temporal-spatial wake model based on the delay time has a better prediction of the spatial distribution and time variation characteristics of the wake.It provides guidance for the control strategy of wind turbine operation process and a reference for wind power prediction.