When the mesh is fine enough to resolve the laminar sublayer, the wall shear
stress is obtained from the laminar stress-strain relationship:

(12.10-42)

If the mesh is too coarse to resolve the laminar sublayer, it is assumed that
the centroid of the wall-adjacent cell falls within the logarithmic region of
the boundary layer, and the law-of-the-wall is employed:

(12.10-43)

where
is the von Kármán constant and
.
If the mesh is a such that the first near wall point is within the buffer region,
then two above laws are blended in accordance with equation Equation
12.10-28.

For the LES simulations in
FLUENT, there is an alternative near wall approach
based on the work of Werner and Wengle [
398], who
proposed analytical integration of power-law near-wall velocity
distribution resulting in the following expressions for the wall shear stress:

(12.10-44)

where
is velocity parallel to the wall,
are the constants,
and
is the near-wall control volume length scale.

The Werner-Wengle wall functions can be enabled using the
define/models/viscous/near-wall-treatment/werner-wengle-wall-fn? text
command.