# 2D case giving 3D result

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July 15, 2011, 14:37
2D case giving 3D result
#1
Senior Member

lore
Join Date: Mar 2010
Location: Italy
Posts: 458
Rep Power: 11
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
Attached Files
 cilindro2D_2.zip (53.1 KB, 16 views)

 July 15, 2011, 18:39 #2 Senior Member     Marco A. Turcios Join Date: Mar 2009 Location: Vancouver, BC, Canada Posts: 716 Rep Power: 21 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?

 July 16, 2011, 04:35 #3 Senior Member   lore Join Date: Mar 2010 Location: Italy Posts: 458 Rep Power: 11 Yes, I could try that! With farField you mean frontAndBack, right?

 July 16, 2011, 06:59 #4 Senior Member   lore Join Date: Mar 2010 Location: Italy Posts: 458 Rep Power: 11 I changed the boundary on frontAndBack as a symmetryPlane but I still can't get a 2D solution.

 July 17, 2011, 07:31 #5 Senior Member   lore Join Date: Mar 2010 Location: Italy Posts: 458 Rep Power: 11 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

 July 17, 2011, 10:45 #6 Senior Member   lore Join Date: Mar 2010 Location: Italy Posts: 458 Rep Power: 11 I'm having some problems with createPatch and createPatchDict. Does anybody know how to use it?

July 18, 2011, 02:14
#7
New Member

Joel Lehikoinen
Join Date: Jun 2011
Posts: 26
Rep Power: 8
Quote:
 Originally Posted by lovecraft22 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.

 July 18, 2011, 08:11 #8 Senior Member   lore Join Date: Mar 2010 Location: Italy Posts: 458 Rep Power: 11 Thank you Joel! I'll have a look!

 July 18, 2011, 14:34 #9 Senior Member   lore Join Date: Mar 2010 Location: Italy Posts: 458 Rep Power: 11 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…

 July 20, 2011, 18:40 #10 Super Moderator   Bruno Santos Join Date: Mar 2009 Location: Lisbon, Portugal Posts: 10,138 Blog Entries: 39 Rep Power: 110 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 __________________ OpenFOAM: FAQ | Getting started Forum: How to get help, to post code/output and forum guide What am I doing/planning: blog/wiki Read this before sending me PM Last edited by wyldckat; July 20, 2011 at 18:42. Reason: fixed typo...

 July 21, 2011, 02:18 #11 Senior Member   lore Join Date: Mar 2010 Location: Italy Posts: 458 Rep Power: 11 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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