Non-physcial solution in the case of triangular mesh from interFoam

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 October 11, 2011, 06:43 #21 Senior Member     ata kamyabi Join Date: Aug 2009 Location: Kerman Posts: 322 Rep Power: 10 Hi Niels Gjoel Jacobsen I know it was in OF1.6 and in the OF1.7 p_rgh has been used but as I know they used p_rgh to make BC more comfortable grad(p_rgh)=0 but as I said I think we can solve this problem by using p in the momentum equation and setting grad(p)=grad(rgh) on the walls. I do not know do you understand me? Good luck Best regards Ata

 October 11, 2011, 22:21 #22 Senior Member   Arjun Join Date: Mar 2009 Location: Nurenberg, Germany Posts: 504 Rep Power: 13 @Ata, Does openFOAM able to run standard test problems with triangular or tet meshes. For example there must be simple tutorial that openFOAM can run. What happens if you keep everything the same and just change the mesh?? Are you able to run the solver. A simple test could be a water column falling etc etc.

 October 12, 2011, 02:54 #23 Senior Member     ata kamyabi Join Date: Aug 2009 Location: Kerman Posts: 322 Rep Power: 10 Hi Yes I examine some different grids and in all triangular grids I had the same problem. Good luck Ata

October 12, 2011, 05:25
#24
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Arjun
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Quote:
 Originally Posted by ata Hi Yes I examine some different grids and in all triangular grids I had the same problem.

Quote:
 Originally Posted by ata Good luck
Thank you. I need lots of luck.

In my case though, my solver works well irrespective of the type of grid (if no negative volume cells exist then usually no problems). Grid type is not much a problem for me.

 October 12, 2011, 05:43 #25 Senior Member     ata kamyabi Join Date: Aug 2009 Location: Kerman Posts: 322 Rep Power: 10 Hi In your cases how much is the density ratio? Good luck Ata

October 12, 2011, 06:16
#26
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Arjun
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Quote:
 Originally Posted by ata Hi In your cases how much is the density ratio? Good luck Ata

1000 : 1

Water air.

Edited to add: So far as per my experience with multiphase simulations with various softwares like Fluent, CFX, StarCCM+ etc, I think the viscosity ratio is much much more problematic than density ratio. 1000 : 1 density ratio is usually not much a problem.

Last edited by arjun; October 12, 2011 at 06:45.

March 6, 2013, 17:25
#27
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Similar issue here. Test problem of a sphere entering a free-surface. Using OF-2.1.0 with sliding AMI interfaces. InterDyMFoam solver although issue occurs with others as well. Results for cavity shape/pinch-off etc. are fine with cartesian grids. When there are just a few non-cartesian cells however, the cavity closes unphysically (see image).

Have a copy of Wemmenhove's paper. Their analysis makes sense to me. I am going to start looking into the evaluation of the snGrad terms in the momentum equation (pd and rho), unless others have some ideas. Has there been anymore discussion on this topic? This is the only thread I could find dealing with the issue.

Also, changing the snGrad scheme from corrected to limited did not fix the issue (results shown here are with the limited scheme).
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 July 8, 2013, 05:34 opposite experience with mesh geometry #28 Member   Join Date: Mar 2013 Posts: 94 Rep Power: 5 Hi to all, this is a very interesting thread. I simulated a multiphase case in which a horizontal closed pipe filled with water is opened at one side at time zero, allowing the gas to enter and liquid to exit the domain. I used a hexahedral mesh with all possible scheme for gradient and divergence scheme (also cellMDLimited version) and the result are very bad. So i tried to change mesh geometry and I used a tetrahedral mesh. In this case the results are very good. So this experience is opposite to yours. The reason is probabily that using a tetahedral mesh there isn't a preferential direction for gradient calculations. What is your opinion? Thank to all

September 4, 2016, 11:59
#29
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Saumitra Joshi
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Quote:
 Originally Posted by arjun In my case though, my solver works well irrespective of the type of grid (if no negative volume cells exist then usually no problems). Grid type is not much a problem for me.
Hey Arjun,

I'm working on building an Adaptive Mesh Refinement algorithm based on the current version, but that also deals with arbitrary meshes. I face a huge problem of spurious currents in my solution - the grid I'm using is mainly tetrahedral.

Could you share what corrections you used to make your code independent of cell shape and orientation?

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