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Old   November 16, 2005, 14:35
Default Mesh in Gambit
  #1
vijaya
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Hi, I considered a helical model and used a strunctured boundary layer meshing. I have two questions: 1. How do u say that the mesh is coarse or fine. Should it be coarse or fine. 2. Can we find how many nodes and cells are present in the meshed structure, like how we can determine in other anlysis softwares like Ansys, Ne-Nastran

Iam new to Gambit and Fluent and would greatly appreciate your answers

Thanks Vijaya
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Old   November 16, 2005, 23:38
Default Re: Mesh in Gambit
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Bharat
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Hi VIjaya,

The coarseness and finess of your grid depends on the accuracy of the solution you are looking for. Generally, if u refine ur grid, the solution improves but this is not in the case of turbulent flow, where u need to consider the y+ plus values also.

hope this helps Bharat
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Old   November 17, 2005, 10:45
Default Re: Mesh in Gambit
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Jason
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In Gambit, under the volume meshing tools, you can right click on the mesh info icon (the icon is a big "i") and you'll notice one of the available commands that shows up is the check mesh command (icon looks like a check mark). Select this command and then pick the volume you're interested in (or select all the volumes). This will list how many cells there are, and will give you a breakdown of the quality of the cells (I can't remember if the default is equi-angle skewness, or equi-size skewness, but you can change this by going to Edit->Defaults, select the "Mesh" tab, and the "Examine" radial button... in the variable list you'll see "Element_3D_Quality" which determines the quality check that is shown when you do a mesh check). It doesn't list the number of nodes, because Fluent is a cell centered solver, and Gambit is really setup to work for Fluent. If the number of nodes is important, then you can see this in Fluent by opening your mesh and then going to Grid->Info->Size.

There's more involved in meshing then just determining if the mesh is "coarse" or "fine". The quality of the mesh is important (skewness of the cells, growth rate from cell to cell, aspect ratio of the cells). As Bharat said, if the model is turbulent, then paying attention to the y+ value of the cells is important (y+ determines where in the BL that the cell center lays... if your y+ value isn't in the proper range for the turbulence model, then you can get questionable results for wall shear stress and other boundary layer properties... there has been a lot of discussion on this forum about y+ and turbulence modeling, so I recommend doing a search of the forum to see what you can find).

Hope this helps, and good luck, Jason
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