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Old   May 10, 2005, 17:21
Default Block meshing using Gambit
  #1
Satish Perivilli
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Hi

I am working on a model that has a cylinder which goes partially through a brick element. I would like to create a block mesh that is unstructured and very fine near the cylinder and becomes structured after a point as we move away. Is there a way to do this using Gambit??

Thanks
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Old   May 11, 2005, 09:47
Default Re: Block meshing using Gambit
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Jason
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I don't know everything about Gambit, but the only way I've been able to accomplish this in the past is to split the volume where I want the transition to occur. If you're using sizing functions, then create those next. Mesh the transition face with a quad mesh. Then finish meshing the local volume with your unstructured mesh. Fluent will use pyramidal elements to make the transition from the unstructured volume mesh to the structured face mesh. Then you can mesh the outer volume with the structured mesh that you had wanted.

Hope this helps, and good luck, Jason
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Old   May 13, 2005, 13:29
Default Re: Block meshing using Gambit
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Satish Perivilli
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Thank you Jason

I have a question here, after doing whatever has been said, I would assume that I would be left with more than one volume in Gambit. Does fluent recognize two volumes while solving the problem, or do I need to unite the volumes in some way to ensure some continuity??

or in other words, Can I directly export the mesh to fluent with these two or more volume meshes and ask it to solve the problem??

thanks
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Old   May 13, 2005, 17:28
Default Re: Block meshing using Gambit
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Jason
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To create your geometry, first create a single volume for your entire control volume. Then break it into smaller, easier to mesh, volumes using the split command with the "connected" option on (on is the default, but just double check to make sure no one's played with the defaults). The "connected" option means that only a single face will exist that the two volumes will share. This way, when you create the surface mesh on this face, it's a surface mesh for both volumes. Do not attach a boundary condition to this face because Gambit recognizes this as construction geometry and exports the mesh as a single volume, and does not write this shared face into the mesh file, so fluent doesn't even know it exists.

Hope this helps, and goodluck Jason
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Old   May 14, 2005, 12:02
Default Re: Block meshing using Gambit
  #5
Satish Perivilli
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Thank you Jason

But there are two more questions here.

1. After I use the split command, it would create two or more volumes, right?? So how do I assign boundary conditions now, for ex: if in the original volume, the bottom surface is wall, there would be two bottom surfaces now after splitting. So do I need to assign wall to both these faces??

2. If i export the mesh, does fluent not read all the volumes?? After doing so, does it solve the problem as I want it to or do I need to do something extra??

Thanks
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Old   May 16, 2005, 12:16
Default Re: Block meshing using Gambit
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Jason
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1) You will have to assign the wall boundary condition to both of those faces. You don't have to define different wall BCs though, just pick all of the faces that represent that one boundary. This is the same for inlets, outlets, etc...

2) Gambit exports all of the meshed volumes as a single volume mesh (unless you specifically define them as different continuums, which is done in the Volume BC defenition panel... normally you don't define a volume bc at all, and gambit automatically writes the model as a "default" continuum which is interpreted in Fluent as a fluid continuum). Since Gambit writes them as a single volume mesh, Fluent doesn't know that this volume was originally made of different volumes. Also, since its written as a single volume, there is nothing else you need to do in Fluent to run the model.

Hope this helps, and good luck, Jason

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