Because of its large scale, Horizontal Axis Wind Turbines (HAWT) usually operate at high Reynolds numbers. However, because of the combined effect of the blade section profile, and the relatively low angle of attack in which the blade operates, laminar-turbulent transition can still occurs at the blade surface, which increases the frictional drag and might affect the performance of the turbines. Then, this paper aims to study the boundary layer transition on wind turbine blades by performing Large Eddy Simulation (LES).

The open-source, DNS code Nek5000 , which is based Spectral Element Method, is used in this study. It has spectral convergence rate and low numerical dissipation, and is highly scalable. An improved version of the LES dynamic Smagorinsky model that was that was initially developed in the code is presented. The validation of this LES model is first performed on a transitional flat plat boundary layer. The results agree well with the reference Direct Numerical Simulation (DNS) in terms of friction coefficient, transition location, and boundary layer velocity profile.

Then a first LES on the NM80 HAWT turbine with angular velocity 1.8rad/s is performed. The turbine model comes from the DAN-AERO MW project, in which transition measurement has been performed on a full scale turbine. To perform a fully resolved Large Eddy simulation, periodic boundary is used to reduce the domain to 1/3 of the whole turbine, and the resolution is only maintained around the blade and in the very near wake. The transition process and its influence on the wind turbine performance is then assessed.