26.17.2 Checking Model Selections

Figure 26.17.4: The Models Tab in the Case Check Dialog Box

The following recommendations appear under the Models tab (Figure  26.17.4):

• Consider realizable k-epsilon in lieu of the standard k-epsilon turbulence model.

  The realizable $k$- $\epsilon$ model is a more recent development of the standard $k$- $\epsilon$ model and differs from it in that the realizable $k$- $\epsilon$ model contains a new formulation for the turbulent viscosity, as well as a new transport equation for the dissipation rate, $\epsilon$, derived from an exact equation for the transport of the mean-square vorticity fluctuation.

  realizable $k$- $\epsilon$ model means that the model satisfies certain mathematical constraints on the Reynolds stresses, consistent with the physics of turbulent flows. For more information on the standard $k$- $\epsilon$ model and the realizable $k$- $\epsilon$ model, visit this section and this section (in the separate Theory Guide), respectively.

  Models Viscous Edit...

  For information on all $k$- $\epsilon$ model options, go to this section in the separate Theory Guide.

• Disable DO/Energy coupling if the optical thickness is less than 10.

  DO/Energy coupling should only be used when the optical thickness is greater than 10. Refer to this section in the separate Theory Guide for more information.

  Models Radiation Edit...

• Verify that an appropriate partial enclosure temperature is specified.

  When using the S2S radiation model, make sure that you use the correct partial enclosure temperature. In most cases this is the ambient temperature, which by default is set at 300K. See Section  13.3.6 for more information.

  Models Radiation Edit...

• Change the under-relaxation factor for the mixing plane model to 1.0.

  If you have created a mixing plane, set the Under-Relaxation in the Mixing Plane dialog box to 1. Look under Global Parameters in Section  10.10.2 for information about the mixing plane under-relaxation.

  Define $\rightarrow$ Mixing Planes...

• Enable the smoothing option for dynamic mesh simulations when remeshing.

  When your case involves the use of dynamic meshes and remeshing is enabled, then it is recommended that you also perform smoothing on the mesh. For a complete discussion of smoothing and remeshing, see Section  11.3.1.

  Dynamic Mesh Dynamic Mesh

• Disable species inlet diffusion for laminar flow with species transport.

  By default, ANSYS FLUENT includes the diffusion flux of species at inlets. In some cases involving species transport and laminar flow, it is recommended that the Inlet Diffusion option in the Species Model dialog box is disabled. For example,

  • If you wish to include only the convective transport of species through the inlets of your domain.

  • If at one of the inlets, the convective flux is very small, resulting in mass loss by diffusion through the inlet.

  Models Species Edit...

  For more information about diffusion at inlets, go to Section  15.1.5.

• Include turbulence interaction for the NOx model.

  When running thermal NOx simulations and your flow is turbulent, then be sure to set the NOx Turbulence Interaction Mode.

  Models NOx Edit...

  In turbulent combustion calculations, ANSYS FLUENT solves the density-weighted time-averaged Navier-Stokes equations for temperature, velocity, and species concentrations or mean mixture fraction and variance. Methods of modeling the mean turbulent reaction rate can be based on either moment methods or probability density function (PDF) techniques. ANSYS FLUENT uses the PDF approach.

  To learn about how this feature is set up, go to Section  21.1.1.

• Consider using the default Schnerr-Sauer or the Zwart-Gerber-Belamri cavitation model.

  When using the mixture multiphase model with the Singhal et. al cavitation model enabled, consider changing it to either the Schnerr-Sauer or the Zwart-Gerber-Belamri cavitation model. Refer to this section in the separate Theory Guide for more information.

  Phases Interaction...