Reply To: Three-dimensional turbulent rough flows – y+ calculation

[Nikolaos Monokrousos]

Thank you for your reply. The system is turbulent, yes. I have been reading regarding the shift in the origin of the y-coordinate that roughness introduces, placing the origin inside the roughness sublayer instead of the wall of interest and it is understood. However, in the case we accept the ANSYS suggestion that the mesh size should be twice the roughness height (equivalent sand-grain roughness height), which other metric could be utilised to qualify the Boundary Layer mesh and the near wall resolution?

In section "7.4.15.3.1.1. Setting the Roughness Parameters" of the ANSYS User's Guide 2023R2 it is stated that: "The advantage of the rough wall formulation using a virtual shift of the wall (Equation 7.120 (p. 1426)) compared to reducing the roughness height as decreases (Equation 7.119 (p. 1425)) is that it eliminates all restrictions with respect to mesh resolution near the wall, and can therefore be used on arbitrarily fine meshes". Assuming that someone is employing the k-omega SST turbulence model which inherently adopts the rough wall formulation using a virtual shift of the wall, is it safe to say that the "restriction" of y+ around 1 is eliminated and it is only a matter of using a fine mesh?