Wind turbine aerodynamics using ALE-VMS: validation and the role of weakly enforced boundary conditions

In this article we present a validation study involving the full-scale NREL Phase VI two-bladed wind turbine rotor. The ALE-VMS formulation of aerodynamics, based on the Navier-Stokes equations of incompressible flows, is employed in conjunction with weakly enforced essential boundary conditions. We find that the ALE-VMS formulation using linear tetrahedral finite elements is able to reproduce experimental data for the aerodynamic (low-speed shaft) torque and cross-section pressure distribution of the NREL Phase VI rotor. We also find that weak enforcement of essential boundary conditions is critical for obtaining accurate aerodynamics results on relatively coarse boundary layer meshes. The proposed numerical formulation is also successfully applied to the aerodynamics simulation of the NREL 5MW offshore baseline wind turbine rotor.