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

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Old   October 11, 2011, 06:43
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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
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Old   October 11, 2011, 22:21
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@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.
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Old   October 12, 2011, 02:54
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Hi
Yes I examine some different grids and in all triangular grids I had the same problem.
Good luck

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Old   October 12, 2011, 05:25
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Quote:
Originally Posted by ata View Post
Hi
Yes I examine some different grids and in all triangular grids I had the same problem.
Thats too bad.


Quote:
Originally Posted by ata View Post
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.
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Old   October 12, 2011, 05:43
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Hi
In your cases how much is the density ratio?
Good luck

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Old   October 12, 2011, 06:16
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Quote:
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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.
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Old   March 6, 2013, 17:25
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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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Old   July 8, 2013, 05:34
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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
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