Modern wind turbines employ thick airfoils in the outer region of the blade with strong adverse pressure gradients and high sensitivity to flow separation, which can be anticipated by leading-edge roughness. However, Reynolds average Navier-Stokes simulations currently overpredict the Reynolds shear stresses near the surface, and the flow separation is not correctly predicted. Hence, these methods are not representative enough to optimize the blade design to avoid flow separation, which becomes relevant for rough blades. While several eddy-viscosity corrections in the (Figure presented.) turbulence model have been previously studied to predict flow separation over smooth airfoils, the present study aims to extend their applicability to airfoils with leading-edge roughness. Two corrections, whose effect on flow physics has not been empirically quantified, are addressed. Particle image velocimetry measurements have been performed on a 30% thick airfoil to quantify the impact of these corrections. The reduction of the eddy viscosity introduced by the corrections leads to a shift of the peak location of the Reynolds shear stresses away from the surface, which, in turn, promotes flow separation and improves the prediction of the mean velocity and the pressure-coefficient distribution. Besides, the ratio between the main turbulent shear stress and turbulent kinetic energy is demonstrated to be lower than the standard value used in the (Figure presented.) turbulence model at the boundary-layer outer edge. Adjusting this ratio for an angle of attack of 0° decreases the error on the predicted lift and drag coefficients from 75% to 3% and from 58% to 39%, respectively.@en

A computational fluid dynamics study is carried out to model the effects of distributed roughness at the airfoil leading-edge using the equivalent sand grain approach and Reynolds-averaged Navier–Stokes equations. The turbulence model k - ω-shear stress transport (SST) is selected to emulate a fully turbulent flow. Three k and ω boundary conditions are studied to model roughness effects. One refers to Wilcox’s boundary condition and the other two refer to Aupoix’s boundary conditions. Besides, Hellsten’s correction is used to ensure Wilcox’s boundary condition compatibility with the shear stress transport limiter. After validating the implementation of these boundary conditions, they are applied to three different airfoils. One of them is a thick airfoil with industrial relevance. For this airfoil, Wilcox’s boundary condition significantly underestimates the roughness impact on aerodynamic coefficients. The pressure gradient simplification in Wilcox’s boundary condition formulation is the driving factor behind this effect. The pressure gradient effect on Aupoix’s boundary condition is minimal.@en