After enabling beta feature access (Introduction), the Wall Roughness settings in the Momentum tab of the Wall dialog box become available for some additional turbulence model combinations:
-equation models with enhanced wall treatment (EWT) or the Menter-Lechner (ML)
near-wall treatment.The wall roughness model must work in wall function mode, which requires fully rough flows (
> 90). In order to avoid a singularity in the downward shift of the
velocity profiles for large roughness heights and low values of 
, Fluent redefines the roughness height based on the mesh refinement (see
section in the Fluent User’s Guide,"Wall Roughness Effects in Turbulent Wall-Bounded
Flows") for these near-wall treatments:The mesh requirement for rough walls in this case is
> 
, so that a reduction of 
for fine meshes (small 
values) is avoided.The following turbulence models based on the
-equation can be combined with rough walls and EWT or ML: all
-
models (that is, standard, RNG, and realizable)Reynolds stress model with the Linear Pressure-Strain option selected
Detached eddy simulation (DES) model with the Realizable k-epsilon option selected
Reynolds stress models based on the ω-equation
Reynolds stress models based on the ω-equation are using the same rough wall model as the two-equation ω-based models like BSL or SST. However, no special calibration and only limited testing has been performed in combination with Reynolds stress models.
In order to avoid a singularity in the downward shift of the velocity profiles for large roughness heights and low values of
, the wall is virtually shifted to 50% of the roughness element height. For
more information about wall roughness for ω-based models, see the section in the Fluent
User’s Guide,"Wall Roughness Effects in Turbulent Wall-Bounded Flows".
The following Reynolds stress models based on the ω-equation can be combined with rough walls:
Stress-Omega
Stress-BSL