Law of the Wall functions
- Check the lower limit of y+. In commonly used applications of wall functions, the meshing should be arranged so that values of y+
at all the wall-adjacent integration points are only slightly above the recommended lower limit y+
= 20-30 (see ). This procedure offers the best chances to resolve the turbulent portion of the boundary layer.
- Check the upper limit on y+. If the Reynolds number is moderate, and the boundary layer only extends to y+ between 300 and 500, there is no chance of accurately resolve the boundary layer, if the first integration point is placed at a location with the value of y+ smaller than this cases direct simulation of the boundary layer can be used instead (see V_FixWall
option).
- Check the resolution of the boundary layer. If boundary layer effects are important, it is recommended to check the resolution of the boundary layer after the computation. This can be achieved by a plot of the ratio between the turbulent and the molecular viscosity, which is high inside the boundary layer. Adequate boundary layer resolution requires several points in the layer.
- Check that the correct form of the wall function is being used to take into account the wall roughness.
- In many practical cases, above recommendations can not be accomplished. If this is the case, some deviation from real phenomena can be expected.