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Some questions about 3D meshing

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Old   September 16, 2009, 12:25
Default Some questions about 3D meshing
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Daniel
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Hello all,

This is my first post. I'm fairly new to Gambit and Fluent. I had some experience, but now I will be using it full time. I've gone through much of the forums to try and gather some information for my problem.

I will be using Gambit and Fluent to mesh and analyze an aircraft in 3D, subsonic flow. For the most part, I would like to extract lift, drag, moment and pressure distribution.

Right now I'm trying to get the thing meshed correctly and I have some questions.

1. Control Volume Size
I remember in 2D subsonic problems, the downstream of the control volume was about 10-15 times the size of the cord. I'm guessing that this holds for a 3D problem also. But I would like to know what the dimensions in the upstream, spanwise (or semispan for symmetry problems) and height directions should be in terms of cord size.

2. Boundary Layer
This is obviously very important to mesh correctly. Is it possible to have an unstructured boundary layer? I know Gambit has the boundary layer functions, but is it wise to define ones own s-function and create a boundary layer this way (using unstructured or structured meshes).

I read that when meshing a surface (or maybe a volume?), that if there are any cell hit tree depth, to increase the maximum background grid level, so I am aware of this problem. But an explanation as to what this all means would be nice (I really want to know the 'why' and not just the 'how').

3. Mesh Zones
I'm using zones here for lack of a better word. Besides the boundary layer, what zones around the aircraft would benefit from a specific type of mesh. The wake area would require a finer mesh. Are there any other areas that I should be concerned with?

If anybody can give me some directions with these (or other areas) that would be great.

Thanks in advance for any and all help.
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