Investigation Of Self-Similarity Characteristics Of Wind Turbine Rotor Wake

The wake effect is one of the main factors affecting the power generation efficiency and wind turbine fatigue life of wind farms.Real-time control of wind turbine rotor wake via wake analytical wake model to mitigate the wake effect is one of the most direct and effective ways to maximize the economic benefits of wind farms.Therefore,investigating the self-similarity characteristics and the streamwise evolution of scaling law of wind turbine rotor wake,and developing a more accurate and physically meaningful analytical wake model have significant importance.In this paper,we study the wake characteristics and the streamwise evolution of the self-similarity state of wind turbine rotor wake under different operating conditions to provide a reference for the establishment of a wake mode with physical significance.The contents are briefed as follows:Firstly,the wake characteristics and the streamwise evolution of the wake selfsimilarity state of the non-yaw rotor under uniform laminar inflow are studied.From the perspective of the characteristic scales,a new self-similar stage is proposed,and combined with the simplified Reynolds-averaged equation of motion,the scaling laws of the wake in this self-similar stage are theoretically derived;then the existence of this self-similarity stage is verified by wind tunnel experiments,and the self-similarity state of the wake and its streamwise evolution is investigated;furthermore,the coefficients of the scaling law of the wake is identified by combining the experimental data and compared with the wind tunnel experimental measurements of the present study.Secondly,the asymmetries of the yaw rotor wake under uniform laminar inflow and the similarities between the yawed rotor wakes under different yaw angles are studied.First of all,the evolution of the asymmetry of the velocity deficit profiles in the self-similarity region with yaw angle is theoretically derived and confirmed by the experimental measurements of the present study.By dividing the wake profiles into two parts on both sides by the center of the profile in the yawed plane,the contribution of the difference in the width of the two parts of the wake profiles and the difference in the two parts of the normalized wake profiles to the wake asymmetry is studied.Then the streamwise evolution of the ratio of the width of the two parts of the wake profiles is studied.And the evolution of the ratio of the width of the two parts of the wake profiles and the two parts of the normalized wake profiles with yaw angle is studied.Furthermore,the streamwise evolution of the yawed rotor wake self-similarity state is studied.By comparing and analyzing the streamwise evolution of the characteristic value of the rotor wake under different yaw angles,the similarity between the rotor wakes under different yaw states is analyzed.Thirdly,the wake characteristics of the rotor wake and its self-similarity under the condition of atmospheric boundary layer inflow are studied.By analyzing the momentum transport at different heights in the incoming flow and wake region,the interaction between the wake of the offshore wind turbine supporting platform wake and the rotor wake is investigated.Furthermore,a wind turbine wake model with consideration of the effect of supporting platform wake is proposed.Finally,the streamwise evolution of the interaction between the individual rotor wakes and the merge process of the individual rotor wakes of a multi-rotor turbine are studied.The influence of the gap flow in the gap region on the mean-field characteristics and spectral characteristics of the multi-rotor wake is analyzed.By comparing the characteristic values and their streamwise evolution of the multi-rotor wind turbine and the single-turbine wind turbine under the non-yawed and yawed conditions,the advantages and disadvantages of the multi-rotor wind turbine compared with the traditional singlerotor wind turbine are investigated.