Dimensionless coefficients for the evaluation of spatial discretization resolution in RANS CFD simulations of Horizontal Axis Wind Turbines

This study presents a computational fluid dynamics (CFD) methodology for predicting the aerodynamic performance of horizontal-axis wind turbines (HAWTs) while reducing the number of evaluations required in mesh independence studies. A geometry-based parameterized approach was developed using the Reynolds-averaged Navier–Stokes (RANS) equations with a Moving Reference Frame (MRF) formulation and the k - ω SST turbulence model, introducing wall distance ( y⁺ ) and Grid-Reduced Vorticity ( GRV ) as dimensionless indicators of mesh adequacy. Systematic mesh refinement was combined with experimental measurements on a commercial wind tunnel and turbine, and the methodology was subsequently verified on a second rotor from the literature. The predicted characteristic curve, power coefficient ( Cᴘ ) versus tip-speed ratio ( TSR ), reproduced the main experimental performance features, with relative deviations within 0 - 15% near and above the optimal TSR ( TSR opt ). Flow-field assessments highlighted refinement-critical zones at the suction-side leading-edge/tip region, trailing-edge wake, tip-vortex trajectory and near wake. From these results, practical mesh-quality reference ranges were established for comparable small-scale HAWT RANS/MRF simulations: blade-surface-averaged y + close to unity, and Rotating-Zone averaged GRV up to approximately 0.026 in the low- TSR , highly vortical regime, decreasing toward 0.010 - 0.006 near and above TSR opt . These indicators provide practical guidance for parameterized mesh generation, potentially supporting CFD-based rotor design, optimization workflows and fluid–structure interaction analyses with reduced mesh-sensitivity effort.