2 above and containing only geometry data at present. If necessary, use pro-STAR’s built-in file browser to locate the file.
2. Output CCM file — The refined mesh solution file, case-fine.ccm. At the end of the mapping operation, this will contain (mapped) solution data as well as geometry data and will therefore be suitable as a restart file for a fine mesh analysis.
3. Instructions on how to assign flow variable values to any fine-grid cells that may lie outside the domain defined by the coarse-grid cells. The available Outside Options are:
(a) Default — use default values, as defined in panel“Initialisation” of sub-folder Liquids and Gases in STAR-GUIde
(b) Nearest — use values from the nearest cell neighbours (c) Zero — use a value of 0.0
Note that the default mapping algorithm is selected by the Use Smap button.
Clicking the Use Tsmap button activates a slightly different algorithm that attempts to enforce global conservation on the fine-grid domain. Other ways in which this option differs from the standard option are as follows:
1. It is not applicable to polyhedral fluid cells
2. Only two Outside Options are available, Nearest and Zero.
3. The volume made up by the fine-grid cells should be fully contained within the volume of the coarse-grid cells. This condition may be satisfied within a tolerance (specified as a volume fraction) entered in the Volume Tolerance box.
Step 7
To visualise the outcome of the mapping operation, use the“Load Data”panel in STAR GUIde’s Post-Processing folder. The mapped solution data file just created may be accessed via the“File(s) tab”and field values loaded via the“Data tab”. The data may then be checked by plotting contours but note that only“Cell Data”should be used for this purpose.
Step 8
If the mapped results are deemed satisfactory, terminate the pro-STAR session without writing a model file (as this would save the original coarse-grid data) and then run STAR to continue the analysis from the mapped solution.
Other noteworthy points are:
• If option Use Tsmap is selected in moving mesh problems containing
removed cells (see “Cell-layer Removal/Addition” on page 12-14), the cell set to be mapped should not include removed cells.
• If any baffles are present in the coarse-grid domain to be refined and mapped, delete the baffles before refinement and redefine them after refinement.
• Do not change the reference temperature in the restart run.
Solution-Adapted Mesh Changes
Section“Solution Control with Mesh Changes” of this chapter shows how to transfer a solution from one mesh to another. In that section,Step 2 simply states
Solution-Adapted Mesh Changes
that you need to perform whatever mesh refinement operations are necessary. This section aims to show how these changes can be made using the solution from a previous run as a guide.
The most frequently used refinement procedures have been assembled in the
“Adaptive Refinement” panel of the STAR GUIde system. This caters for mesh refinement based on the results of a previous run. One may employ a refinement operation based on either
• flow variable gradients, or
• solution residuals.
Both types of data are stored in the solution (.ccm) file and one may then choose the flow variable and selection method to be employed. A typical refinement session would consist of the following steps:
Step 1
Go to the Analysis Preparation/Running folder in the STAR GUIde system and open the“Adaptive Refinement”panel. In the“Refinement Criteria”tab, choose a criterion by selecting the appropriate sub-tab. The flow variable on which to base the refinement depends on the application. For flow-dominated problems, the velocity magnitude or the turbulence kinetic energy have been found to give good results; for chemical reaction- dominated problems, the temperature might be a better choice. Note that:
• Using the Percent of Cells selection method allows you to closely control the number of cells selected for refinement
• You may perform multiple selections based on different variables and different criteria; the selection results are accumulated into a compound cell.
set
• You may abandon your current selection at any stage and start again by clicking the New button
Step 2
Go to the“Set Modifications” tab and select set modification options, e.g.
• The Near Wall Cell Options may be used to ensure that near-wall cells are left unrefined when limitations on the magnitude of y+ need to be observed.
• The final set can be ‘grown’, i.e. expanded to include neighbouring cells, to account for inaccuracies in the error estimate and to prevent large differences in refinement level between neighbouring parts of the mesh.
Check the set to be refined visually by plotting it. If necessary, last-minute
modifications can be made to this set using the standard pro-STAR cell set utilities (see “Set Manipulation” on page 2-21).
Step 3
Once the required cells are finally selected, the“Refine” tab enables you to
• refine them using a simple 2× 2 × 2 subdivision,
• recreate the cell connectivity,
• prepare the resulting new model for the next run. This last step entails
mapping the old solution to the new geometry, changing the solution mode to a restart run from the new (mapped) .ccm file and redefining the monitoring
Solution-Adapted Mesh Changes
and pressure reference cells, if these were within the area that has been refined.
Note, however, that there are many other ways to proceed. Consider filling the volume occupied by the chosen cells with one or more blocks (maybe after a little padding out) and then specifying block factors to build a mesh with progressive, concertina-style refinement. You may also choose to fill the volume with a completely new mesh built by any pro-STAR operation or imported from an external package (see “Importing Data from other Systems” on page 3-1 of the Meshing User Guide). The reverse effect, coarsening the mesh, may by achieved via one of the above methods or by using the CJOIN command.