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-   -   can OpenFoam model a pole in Cylindrical mesh?? (https://www.cfd-online.com/Forums/openfoam-solving/143505-can-openfoam-model-pole-cylindrical-mesh.html)

Dan1788 October 26, 2014 20:03

can OpenFoam model a pole in Cylindrical mesh??
 
1 Attachment(s)
I am making a 3D cylindrical mesh for LES computations of premixed flames.

I would like to know if OpenFoam can correctly model singularities or poles at the origin (as shown in the attached figure) correctly, or would I have to mesh my geometry in a different manner.

Would really appreciate any help on this topic. Thanks!

ChristoBeers October 27, 2014 16:17

I had previously tested this with rhoPimpleFoam, and did notice abnormal action along the cylinder axis (center of the "pie slices") where the cell skewness gets really large. I then tried rounding out one square hex, but this introduced abnormalities where the corners were stretched out (probably for the same reason). I then meshed a square in the center of the circle which simulated properly.

I honestly didn't spend too much effort trying to see if there were more advanced solver options to account for skewedness, I just changed the mesh. Somebody else with more experience may speak to your exact question.

Good luck!

RodriguezFatz October 28, 2014 04:05

I am wondering: why..? I mean, people use o-grids for this normally. I didn't really question this up to now, because I thought this is pretty common. Can you explain, why you prefer this way of meshing?

ChristoBeers October 28, 2014 12:11

You are absolutely right, people use o-grids. It may have been my specific mesh/configuration/BC, but there were false temp/density iso's which protruded down the cylinder axis which should not have been the case. I was merely warning the OP that it is possible if he's not careful. As I said, I didn't play with it too much because it was simple enough for me to change the grid.

To keep an o-grid in my system I had calculated an excessively dense mesh in the center to keep the skewness down (increasing #/meter of "onion shells" around the axis where the "pie slice" tips narrow to zero @ the center). I have very little experience in CFD, but in my simulation, the denser mesh & running >3 nonOrthogonalCorrectors will slow me down, and I guessed a nice cubic in the center may help the solver converge more rapidly...? I wanted to spend the mesh density near the walls where there's something more interesting going on. Am I way off?

Dan1788 October 28, 2014 13:14

Even I am modeling my mesh using an O-grid but was wondering if OpenFoam could model poles because for an axisymmetric grid it is able to take into account pole formation.

Anyways thanks for your reply Chris! :)

chun May 30, 2017 22:03

3 Attachment(s)
Although it might be late for you, but I do have what you want.

You can change the length and radius from the .m4 file.
Using the following command, you can get the blockMeshDict from the .m4 file.
Code:

m4 circle.m4 > blockMeshDict


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