I think that the most hard to grasp aspect of turbulence modeling in SimScale is the use of automatic wall functions. I would like to focus on two turbulence models: the RANS k-omega SST and the DES of Spalart-Allmaras. In both it seems that automatic wall functions have been extensively used to promote an almost monotonic error decrease as the meshes are refined near the walls, bringing the adjacent to wall cell centers from y+ > 30 (inertial sublayer where the standard wall function would work) to the y+ < 1 range (laminar sublayer, where these turbulence models could be used without any wall function). And here came my questions (not very good ones, I realized later, see my next post below).
For the Spalart-Allmaras (under the LES label) SimScale uses the Spalding wall function ( OpenFOAM: nutUSpaldingWallFunctionFvPatchScalarField Class Reference ) for wall shear stress calculation (when Wall function BC option is selected)? This wall shear stress is used to apply no-slip boundary condition (BC) on the momentum equation while nuTilda = 0 is taken as BC (at walls) for the nuTilda transport equation, right?
For the k-omega SST we need BC’s for momentum, k and omega. SimScale uses the Spalding wall function for obtaining wall shear stress (used in momentum BC) and k at the center of the cell adjacent to the wall (through the third equation in Near-wall treatment for k-omega models -- CFD-Wiki, the free CFD reference ) while the omega value is taken from square root of the sum of squares of the values calculated (as also shown in this same link). Right or wrong?