Grid Merge
 

I tried to generate grids using unstructured and structured meshes for different zones in seperate mesh files , and later to merge them together using Tgrid. In Fluent, I used interface definition to merge the non-conformal grids for the surfaces that are overlapped.

However, after pairing up the non-conformal surfaces using grid interface definition, the grid check failed. There were indications in the console window: negative volume appear, right and left handed surfaces. Fluent couldn't proceed after the warning.

By the way, the case was a VOF model with a quite big computational domain.

Please give your advices and comments on the possible reasons for the above problem.

Thank you very much in advance.

Re: Grid Merge
 

Either your mesh or geometry has a defect - do a check on both geometry and mesh in Gambit before exporting...

Re: Grid Merge
 

Thank you for your response. Before pairing up the overlapping surfaces, there is no problem for grid checking. Just after the grid interface definition, the grid check fails. Thanks again.

Re: Grid Merge
 

If neither your geometry nor your individual mesh files have any problem, I would recommend you to also try merging the different meshfiles using the "tfilter tmerge3d (or tmerge2d)" command, on the terminal console window before going to fluent.

When I did this way, I did not have any problem with grid check. In my problem, I merged about 6 different mesh files.

Re: Grid Merge
 

I would also like to add that, in case your grid check fails "after" "creating the interfaces" in "Grid interfaces" panel and no such problem "before", then I would recommend you to please check if any of your interfacing surfaces contain "periodic" edges. "Sometimes" this may be one reason to give such a problem.

Please note that, in case you do have some periodic edges as part of your interfacing surfaces, it is a good idea to define periodic zones before "creating" interfaces. Once you create interfaces, FLUENT cannot make those zones periodic, "if they have any periodic edges".

Regards,

Sridhar.

Re: Grid Merge
 

Thank you so much for your valuable advices. Actually, there is no periodic edge in my model. Could you tell me how to start tfilter tmerge3d? Is it included in the standard package of Fluent software? Looking forward to your reply. Thank you again.

Grid Merge
 

Hello ,

After you have your independent mesh files, before invoking Fluent, on the terminal console command prompt just type "tfilter tmerge3d". This is a standard command that is incorporated in the Fluent package itself. When you do that, from then on it is interactive, it will first ask for the name of the 1st mesh file that you want to include in merging. Then it will ask if you want to scale the grid (in x,y or z directions- if you donot want to scale the grid just type in 1 1 1) and then it will ask if you want to traslate the grid to another co-ordinate location. If you donot want just type 0 0 0. Then it will ask if you want to rotate the grid about any axis and through what angle. If you donot want then just type 0 0.

Then press "enter".

Then it will prompt for another mesh file. And if you want to merge the same mesh with itself but by translating or rotating, you can do so. Else you can enter the name of another mesh file.

You can similarly merge as many mesh files as you want by following the same procedure.

When you are done with all the mesh files, and donot want to merge any more, when it propmts for a new mesh file to merge, just press "enter" then it will understand that input mesh files are over and then it will ask for the name of the "merged" mesh file. Once you give the "Output" file name, it will start merging. After this is done then you can start fluent and then read in this final output mesh file.

You can find the same and more information about using the "tfilter tmerge3d" command in Fluent users' guide, Volume 1, in the topic on Non-Conformal Grids in Chapter on Reading Grids.

And, as you are aware it is always a good idea to check your grid as soon as you read in the mesh.

I hope this would be of some use to you. Please do let me know if it solved your problem. Thanks and Regards,

Sridhar.

Re: Grid Merge
 

Dear Sridhar,Thank you for your detailed advices.

I would also be interested to know how to use these utilities in Windows versions of FLUENT.

*EDIT*
I found out myself: To use theses utilities on Windows, browse to the Fluent.Inc folder and then the 'utility' sub-folder.