Analysis of the anisotropy aerodynamic characteristics of downstream wind turbine considering the 3D wake expansion based on coupling method

The inhomogeneous wake velocity distribution caused by the variation of relative position has a great impact on aerodynamic anisotropy characteristics of downstream wind turbine (WT). To accurately and efficiently evaluate the aerodynamic anisotropy of the downstream WT under wake inflow, an aero-elastic-servo model combined with the 3D Jensen-Gaussian (3DJG) wake model and OpenFAST was proposed in this paper. The accuracy of the model was verified by comparing with Jonkman's research. The effect of the relative installation position of the two 5 MW turbines on the aerodynamic anisotropy of the downstream WT was analyzed. Results indicate that the power loss of the downstream WT can be up to 17.47%-51.53% in the case investigated in this study. Due to the 3D wake expansion and the momentum mixing effect, relative axial distance and relative radial distance alternately become the dominant factor for rotor power recovery when y/R < 1 and y/R >= 1. The phenomenon mentioned in rotor power is also indicated in downstream rotor torque and thrust. Due to the inhomogeneous wind velocity distribution of the wake inflow, the standard deviation and average value of the blade root flapwise moment (BRFM) suffered by downstream WT are 10.84% and 24.30% larger than that suffered by upstream WT respectively. This paper provides better guidance for optimizing the WT layout and quantification of the wake effect on downstream WT.