Page 107 - ansys

Including Thermal Effects
If the enhanced wall treatment is used, you may include thermal effects by enabling the Thermal
Effects option under Enhanced Wall Treatment Options. Thermal Effects option is enabled if the ideal
gas law is selected for the fluid density in the Create/Edit Materials dialog box.
Including the Wall Reflection Term
If the RSM is used with the default model for pressure strain, ANSYS FLUENT will, by default, include
the wall-reflection effects in the pressure-strain term. Note that wall-reflection effects are not
included if you have selected the quadratic pressure-strain model.

Solving the k Equation to Obtain Wall Boundary Conditions
In the RSM, ANSYS FLUENT, by default, uses the explicit setting of boundary conditions for the
Reynolds stresses near the walls, with the values computed. The turbulent kinetic energy, k, is
calculated by solving the k equation obtained for normal stresses. To disable this option and use the
wall boundary conditions given in
Customizing the Turbulent Viscosity

If you are using the Spalart-Allmaras, k- , k-ω, DES, or LES models, a user-defined function can be used
to customize the turbulent viscosity. This option will enable you to modify µt in the case of the Spalart-
Allmaras, k- , and k-ω models, and incorporate completely new subgrid models in the case of the LES
model. More information about user-defined functions can be found in the separate UDF Manual.

In the Viscous Model dialog box, under User-Defined Functions, select the appropriate user-defined
function in the Turbulent Viscosity drop-down list. For the LES model, select the appropriate UDF in
the Subgrid-Scale Turbulent Viscosity drop-down list.
Customizing the Turbulent Prandtl and Schmidt Numbers
If you are using the standard or realizable k- model or the standard k-ω model, a user-defined function
can be used to customize the turbulent Prandtl and Schmidt numbers. This option will allow you to
calculate σk and either σ or σω (depending on the choice of either k- or k-ω model) by using a UDF. You
will also be able to calculate the value of the energy turbulent Prandtl number.
In the Viscous Model dialog box, under User-Defined Functions, select the appropriate user-defined
function from the drop-down lists under Prandtl and Schmidt Numbers. Options include: TKE Prandtl
Number, TDR Prandtl Number (k- models only), SDR Prandtl Number (k-ω model only), Energy
Prandtl Number, Wall Prandtl Number, and Turbulent Schmidt Number.
Modeling Turbulence with Non-Newtonian Fluids

If the turbulent flow involves non-Newtonian fluids, you can use the define/models/
viscous/turbulence-expert/turb-non-newtonian? Text command to enable the se-lection of non-
Newtonian options for the material viscosity.

100