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2D case giving 3D result

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Old   July 15, 2011, 14:37
Default 2D case giving 3D result
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Hi all;
trying to solve a simple 2D circular cylinder with simpeFoam but the results I'm getting are actually 3D results, as you can see from the following picture which shows the pressure on the cylinder surface.



The cylinder axis is in the z-direction (so the cylinder lies on the x-y plane). I only have one cell in z-direction and both the planes of the domain parallel to the x-y plane are set as empty.

Could you please check my case directory and tell me what I am doing wrong?

Thank you!

Lorenzo
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Old   July 15, 2011, 18:39
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Looking at your fields, there is a fluctuation in the z component of you simulatiom, which shouldn't happen when you doing a 2D simulation. Your boundary conditions look okay, though I'm curious why you chose slip conditions on the farField; wouldn't it be better to make it an outletInlet?
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Old   July 16, 2011, 04:35
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Yes, I could try that! With farField you mean frontAndBack, right?
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Old   July 16, 2011, 06:59
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I changed the boundary on frontAndBack as a symmetryPlane but I still can't get a 2D solution.
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Old   July 17, 2011, 07:31
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I found out the problem: I meshed the cylinder using snappyHexMesh which always gives a 3D mesh. In fact my cylinder surface has more than one cell in Z-direction although my block mesh has only one.
So what we can do is:

1. Use blockMesh only without running snappyHexMesh. This is fine in this case for a simple circular cylinder but is not for different (even simple) geometries, such as an airfoil.

2. Extrude the mesh from snappyHexMesh you have on a plane, using extrudeMesh. Haven't tried that yet. I'll do it later. The tutorial I'll be referring to will be

/tutorials/incompressible/pimpleDyMFoam/wingMotion/wingMotion2D_simpleFoam
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Old   July 17, 2011, 10:45
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I'm having some problems with createPatch and createPatchDict. Does anybody know how to use it?
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Old   July 18, 2011, 02:14
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Quote:
Originally Posted by lovecraft22 View Post
I'm having some problems with createPatch and createPatchDict. Does anybody know how to use it?
Probably a good place to start is the example createPatchDict-file in $FOAM_UTILITIES/mesh/manipulation/createPatch/createPatchDict.
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Old   July 18, 2011, 08:11
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Thank you Joel! I'll have a look!
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Old   July 18, 2011, 14:34
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I managed to solve the case but I'm getting some funny results. The velocity, for example, lies in an extremely wide range (-7000, +7000) m/s while the inlet velocity should me 30 m/s. Also the overall field, thus being 2D, doesn't seem to be that of a circular cylinder…
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Old   July 20, 2011, 18:40
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Greetings to all!

I'm probably late in writing about this, but I just re-found this example: http://openfoamwiki.net/index.php/Ma...Examples/2DsHM - basically it's a step-by-step guide on how to generate a 2D mesh using snappyHexMesh.
This subject has already been discussed in the past here in the forum, but I didn't manage to find the time to search for it... but now I stumbled on this handy wiki page, so I remembered to post it here.

Best regards,
Bruno

Last edited by wyldckat; July 20, 2011 at 18:42. Reason: fixed typo...
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Old   July 21, 2011, 02:18
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Thank you wyld. I already knew that tutorial but I still can't figure out why I'm getting so strange results…
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