5.3.10 Reading Multiple Mesh Files

There may be some cases in which you will need to read multiple mesh files (subdomains) to form your computational domain. Some examples are listed below:

• If you plan to solve on a multiblock mesh, you can generate each block of the mesh in the grid generator and save it to a separate grid file.

• For very complicated geometries, it may be more efficient to save the mesh for each part as a separate grid file.

Note that you do not need to ensure that the grid node locations are identical at the boundaries where two separate meshes meet; FLUENT can handle non-conformal grid interfaces. See Section  5.4 for details about non-conformal grid boundaries.

The procedure for reading multiple grid files is as follows:

1.

Generate the grid for the whole domain in the grid generator, and save each cell zone (or block or part) to a separate grid file for FLUENT.

!! If one (or more) of the grids you wish to import is structured (e.g., a FLUENT 4 grid file), you will need to first convert it to FLUENT format using the fl42seg filter described in Section  5.3.8.

2.

Before you start the solver, use either TGrid or the tmerge filter to combine the grids into one grid file. The TGrid method is more convenient, but the tmerge method allows you to rotate, scale, and/or translate the grids before they are merged.

• To use TGrid, follow the procedure below:

  (a)

  Read all of the grid files into TGrid. When TGrid reads the grid files, it will automatically merge them into a single grid.

  (b)

  Save the merged grid file.

  See the TGrid User's Guide for information about reading and writing files in TGrid.

• To use the tmerge filter, follow the procedure below (before starting FLUENT):

  (a)

  For 3D problems, type utility tmerge -3d. For 2D problems, type utility tmerge -2d.

  (b)

  When prompted, specify the names of the input files (the separate grid files) and the name of the output file in which to save the complete grid. For each input file, you can specify scaling factors, translation distances, or a rotation angle. In the example below, no scaling, translation, or rotation is performed.

  user@mymachine:>utility tmerge -2d
  
  Starting /Fluent.Inc/utility/tmerge2.1/ultra/tmerge_2d.2.1.13
  
  Append 2D grid files.
  tmerge2D Fluent Inc, Version 2.1.11
  
   Enter name of grid file (ENTER to continue) : my1.msh
  
  
   x,y scaling factor, eg. 1 1             : 1 1
  
  
   x,y translation, eg. 0 1                : 0 0
  
  
   rotation angle (deg), eg. 45            : 0
  
  
   Enter name of grid file (ENTER to continue) : my2.msh
  
  
   x,y scaling factor, eg. 1 1             : 1 1
  
  
   x,y translation, eg. 0 1                : 0 0
  
  
   rotation angle (deg), eg. 45            : 0
  
  
   Enter name of grid file (ENTER to continue) : <ENTER>
  
  
   Enter name of output file               : final.msh
  
  
  Reading...
    node zone: id 1, ib 1, ie 1677, typ 1
    node zone: id 2, ib 1678, ie 2169, typ 2
        .
        .
        .
  done.
  Writing...
    492 nodes, id 1, ib 1678, ie 2169, type 2.
    1677 nodes, id 2, ib 1, ie 1677, type 1.
        .
        .
        .
  done.
  Appending done.
  

  In the above example, where no scaling, translation, or rotation is requested, you could simplify the inputs to the following:

  utility tmerge -2d -cl -p my1.msh my2.msh final.msh
  

3.

Read the combined grid file into the solver in the usual manner (using the File/Read/Case... menu item).

For a conformal mesh, if you do not want a boundary between the adjacent cell zones, you can use the Fuse Face Zones panel to fuse the ``overlapping'' boundaries (see Section  5.7.7). The matching faces will be moved to a new zone with a boundary type of interior. If all faces on either or both of the original zones have been moved to the new zone, the original zone(s) will be discarded.

!! If you are planning to use sliding meshes, or if you have non-conformal boundaries between adjacent cell zones, you should not fuse the overlapping zones. You must instead change the type of the two overlapping zones to interface (as described in Section  5.4).