Effect of Rainfall on Evolution of the wind turbine wake：A LES Study

The rainfall directly affects wind turbine operation by eroding the turbine blades and changing their aerodynamic performance, however, little research has been conducted on the effects of rainfall on wake evolution. The present study simulates the impact of rainfall on wind turbine wake using a coupled LES-ADMR model, in which a double Euler method is employed for the rainfall injection. The numerical simulation results indicate that the rainfall reduces the wake wind speed in the sweep area while increasing it in the outer region of the upper blade tip, reaching up to 2.1% for increment. Rainfall also weakens the turbulence in the near wake and the outer region of the top tip (as much as 2.0%), with the influence extending up to 10 diameters downstream the wind turbine. These modifications are positively correlated with the rainfall intensity and inversely correlated with wind speed. By analyzing the rainfall-induced changes in MKE (Mean Kinetic Energy) and TKE (Turbulent Kinetic Energy) budget terms, the study reveals that the alteration of turbulent radial transport of MKE is the main cause of changes in wind speed, while the variation of shear production of  TKE is responsible for the turbulent intensity changes. The rainfall-induced change of  reynold stress u'w' is the root cause of the above phenomenons.