Adapting mesh

The usual mode of the computation of the turbulent convection with CrysMAS is the hybrid method with application of the block-structured-mesh for the flow domain. Additionally the turbulent fluid flow can be computed on a pure unstructured mesh. The numerical method on the unstructured mesh consumes much larger computational time, its stability is worse in comparison with the method based on the structured mesh. The appropriate mesh quality in the boundary layers is much more difficult to achieve than using the structured mesh. Therefore a special procedure for the adaption of the unstructured mesh was developed for the turbulent fluid flow computation.

The implementation of turbulence model in CrysMAS on the unstructured mesh may require a special mesh at the boundary between e. g. the gas and solid regions. The normal computed mesh can be adjusted in order to fit the needs.

This function does not change the number of degrees of freedom or the mesh topology. It causes a shifting of the nodes from the middle of the selected region towards the region boundary (boundary layer). It can be applied after the generation of the default mesh and either before or after the computation of the view factors.

  1. Before adapting mesh, set required mesh parameters by generating the normal mesh.

    Some minimum density of the numerical mesh is required in the turbulent boundary layer in order to calculate the transport of heat, momentum and special values of the turbulence model. The required mesh density depends on the Reynolds number. A typical mesh size of 3 mm or less is advised at the boundary between convective gas region and solid body. In the center of the convective region the mesh size should be 15 mm or less and the progression denominator for the transition in the mesh density from the boundary toward the region center should be 0.15.

    • set the Edge length to 0.015 and Fit slope to 0.15 for convective gas region.
    • set the Edge length to 0.003 for the boundaries of convective gas region, excepting the symmetry axis.
    • recompute the mesh by selecting Computation > Generate mesh or clicking on   tool button.

    For details about setting mesh parameters see Unstructured mesh Properties.

  2. Select Computation > Adapt mesh.

    The Adapt mesh dialog opens and you set the mesh adaption parameters.

    Setting mesh adaption parameters 

    Figure 31. Setting mesh adaption parameters

  3. Select the region for mesh adaption process, e.g. the gas region.

    The adaption could be generally applied for a group of regions.

    You can either manually select the regions, if the adapt for selected regions option is checked,

    or

    the program automatically selects all regions involved into a physical model, if the adapt for physical phenomena option is checked. The list of the available physical models is provided in this case, the default is turbulent_energy. In this case you have to set the corresponding physical phenomena to the adapted regions before adapting the mesh, see Physical Phenomena.

  4. Set the strength of the mesh deformation

    It is defined according to two methods:

    • by indicating the reduction degree for the distance of last node to the region boundary (the decrease distance by factor of should be checked).

    • by indicating the absolute distance of last node to the wall (the distance last node - boundary should be checked).

    Adjust parameters for mesh refinement, if desired.

  5. Click on Apply to adjust the mesh.

Note

The mesh adaptation can be applied not only for calculation of the turbulent fluid flow but for any problem where the inhomogeneous numerical refinement in the region core and on its boundaries is necessary, for example by the species transport in the melt.
Related Procedures

Adjusting the mesh

Related Dialogs

Adapt mesh