The CFD simulation based prediction of the NREL WT
The choice of the rotating reference frame alongside with the axisymmetrical far-field boundary conditions allows for the steady state modelling of the rotor flow. 3D RANS model for incompressible fluid with SST k–ω turbulence model is applied. The SST model is well suited for the blade-flow problems with moderately large separation zones that are expected along the blade suction side. Fully turbulent flow is assumed while using SST model.
The impact of the computational domain size, mesh density and convergence criteria on the power prediction were investigated while observing the necessary computational effort.
It was concluded that the largest AA 29504 of the computational effort with the least loss of prediction accuracy for important physical phenomena was achieved with the size of the computational domain 3D in diameter and 5D in length, while reducing mesh density.
A high quality grid with tetrahedral cells was used. Globally, the maximum allowable cell size was set to 1 m. The first local refinement restraining the maximum cell size to 300 mm was applied in the cylinder-like subdomain with 1.2D (12 m) diameter, stretching 0.2D (2 m) upstream and 0.6D (6 m) downstream of the rotor. The grid sizing at the pressure and suction side of the blade was 30 mm and 15 mm respectively with further refinement along the leading edge of the blade.