Tdyn reference manual
- 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 Figure
35). 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 100. In
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.