Setting turbulent convection on unstructured mesh parameters

Normally the turbulent convection can be computed using the structured meshes. The algorithm on the structured mesh is more stable for the turbulent flow applications. The standard k-ε turbulence model with wall functions is used on both types of the numerical meshes.

The standard k-ε turbulence model requires the solution of two additional highly nonlinear transport equations of the kinetic energy of the turbulent movement and for the eddy dissipation rate. These values are the field variables of the turbulence model. The secondary field variable is the turbulent viscosity that is derived algebraically from the computed values of k and ε. The turbulent viscosity affects the diffusive momentum transport described in the Navier-Stokes equations. Additionally the effective heat conductivity value is affected by the turbulent viscosity for the thermally coupled flows.

The computation of the turbulent flow on the unstructured mesh is also implemented. Special numerical parameters for the turbulence treatment on the unstructured mesh are available in the Turbulence dialog tab. They manage the solution procedure of k-ε turbulence model equations.

  1. Select Computation > Convection parameters > Turbulence tab.

    The Turbulence tab in the Convection parameters dialog opens:

    Turbulence tab in the Convection parameters dialog 

    Figure 24. Turbulence tab in the Convection parameters dialog

  2. The underrelaxation factors for turbulent energy and eddy dissipation equations are applied separately, obvious both linearized equations are solved together in the same matrix equation. The recommended value for both underrelaxation factors is 0.1.

    Change the underrelaxation of turbulent energy and eddy dissipation, if necessary.

  3. Set the underrelaxation for turbulent viscosity to a small value ( < 0.1 ). Because of the strong underrelaxation the calculated turbulent viscosity will be changed iteratively very slowly. But in case of weaker underrelaxation, the turbulence equations might diverge.

    Change the underrelaxation of turbulent viscosity, if necessary. The recommended value is 0.08.

  4. Set the convergence criteria Max. inner iterations and Desired residuum, if desired.

  5. The next parameter is required in order to achieve a stable solution behavior. The computation of the turbulent viscosity in the triangles laying at the boundary fluid-solid is avoided at the beginning of the calculation because of the numerical stability reasons.

    The turbulent viscosity will be updated everywhere after the residuum of the k-ε turbulence equations have achieved some critical value. This value is prescribed in the Set last triangle at parameter. By setting of the larger residuum value the calculation of the turbulent viscosity in the last triangles begins earlier.

    Adjust Set last triangle at parameter, if desired.

  6. Click on Apply and Close.

    or

    Click on OK to apply the changes and to close the dialog.

Related Procedures

Computing Turbulent Gas Convection on unstructured mesh

Related Dialogs

Turbulence