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Bifurcation explode at intersection

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Old   June 28, 2011, 04:10
Default Bifurcation explode at intersection
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Guifan Li
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Hi everyone,

I am simulation the blood flow in the bifurcation( I used Gmsh to mesh the bifurcation and import it to Openfoam). When I icoFoam it, the courant number always explode at the intesecation which you can view it one the picutures below.

It seems like the velocity is reflected by the sharp corner and pierce the wall then cause it explode.

I am quite new to Openfoam and not sure whether it is because my mesh or because of other reasons.

Can anyone point out what's going wrong?

Screenshot.jpg
Screenshot.jpg

Screenshot-1.jpg
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File Type: jpg Screenshot-2.jpg (13.0 KB, 13 views)
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Old   June 28, 2011, 04:13
Default My p and U file
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p file
dimensions [0 2 -2 0 0 0 0];
internalField uniform 0;
boundaryField
{
wall
{
type zeroGradient;
}
inlet
{
type zeroGradient;
}
bent_outlet
{
type fixedValue;
value uniform 0;
}
straight_outlet
{
type fixedValue;
value uniform 0;
}
}
U file
dimensions [0 1 -1 0 0 0 0];

internalField uniform (0 0 0);

boundaryField
{
wall
{
type fixedValue;
value uniform (0 0 0);
}
inlet
{
type fixedValue;
value uniform (0 0 0.05);
}
bent_outlet
{
type zeroGradient;
}
straight_outlet
{
type zeroGradient;
}
}

Last edited by liguifan; June 28, 2011 at 04:43.
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Old   June 28, 2011, 04:20
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Can you check whether there's any "funny" cell in that region?
I would open the mesh in paraview (or whichever software you prefer) and do some slices...
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Old   June 28, 2011, 04:48
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Quote:
Originally Posted by lovecraft22 View Post
Can you check whether there's any "funny" cell in that region?
I would open the mesh in paraview (or whichever software you prefer) and do some slices...
Hi lore,

Thanks for replying my post.

I tried to use paraview to slice it. First of all , there is no hole in that region and I didn't find any wired cells in that region.

Could other reasons lead to explode?
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Old   June 28, 2011, 06:06
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Can you please post a picture of that region? just the mesh.
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Old   June 28, 2011, 06:26
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Picture 4.jpg

Screenshot-3.png

Screenshot-4.png

Picture 2.jpg

Picture 3.jpg

Screenshot-4.png
Quote:
Originally Posted by lovecraft22 View Post
Can you please post a picture of that region? just the mesh.
Hi lore,
Here are some pictures of the mesh, please let me know if you need more.
thanks
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Old   June 28, 2011, 06:29
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Screenshot-5.png
and this thanks
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Old   June 28, 2011, 07:03
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Could you please post a slice of the region where you're having the blown up?
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Old   June 28, 2011, 07:52
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Screenshot-6.png

Screenshot-7.png

Screenshot-8.png

Screenshot-9.jpg

Hi lore,

It is quite hard to slice the exact point where it blow up, but here are some mesh slice that is the blow up region. hope it helps .

If you want, I can send you my file which is too large to upload here.

Cheers
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Old   June 28, 2011, 08:05
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Guifan, you should slice the pipe with a zx plane, ie a plane wich lies in the flow direction.
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Old   June 28, 2011, 08:16
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Hi lore, Sorry for the misunderstanding.

Screenshot-10.jpg

Screenshot-11.jpg

Screenshot-12.jpg
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Old   June 28, 2011, 08:44
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Mmm, your mesh seems to be ok...Maybe you should wait for somone with more experience than me...
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Old   June 28, 2011, 08:56
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lore, thanks for that anyway
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Old   June 29, 2011, 09:36
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Have you tried changing the time step?
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Old   July 1, 2011, 04:28
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Quote:
Originally Posted by lovecraft22 View Post
Have you tried changing the time step?
Hi lore,

I tried to change the time step from 0.0001 to 0.000001 and it works. But now I reduced the element sizes from 150,000 to around 60,000 with time step 0.0001. It works as well.

Sorry for the late reply.
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Old   July 1, 2011, 04:34
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Yes, that's what I meant: in both cases you changed the Courant number. I only mentioned the time step and not the cell size because I thought you wanted to keep the mesh the same.
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