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Flow through circular pipe not converging

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Old   June 12, 2013, 11:17
Default Flow through circular pipe not converging
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Tanjina Afrin
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Hi,
I am trying to solve flow through a circular pipe from a rectangular reservoir(3-D). I used VOF, turbulent, energy equation model , enabled gravity, transient time. my time step is 1e-8. I commanded to run upto 1600 run. After 932 run, it says that "courat number is greater that 250, velocity is diverging. please check the solution and reduce the time step if necessary". I tried with smaller time step, but it didn;t complete the full run.

I created and meshed the geometry by workbench. I couldn't find the problem why it's not running. Could anybody help me? How can I find the appropriate mesh size for run?

I have attached the contour of symmetry plane after 932 run.

Thanks in advance.
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File Type: jpg Trial 4.jpg (51.7 KB, 12 views)
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Old   June 12, 2013, 14:21
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ousegui
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Hi
your time step is small enough, so I advise you to improve your mesh
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Old   June 12, 2013, 14:29
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Tanjina Afrin
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Thank you. Right now the mesh element size is 6E-003m. I used workbench's default mesh which is triangular. And the dimension of the geometry is : reservoir size 2mm height, 2mmX2mm base, Pipe size : 6 mm length, 1 mm dia.

Should I use more fine mesh ?
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Old   June 12, 2013, 14:31
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Can u send a picture of your meshing?
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Old   June 12, 2013, 14:40
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Tanjina Afrin
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Yea, off course. Please find the following images of mesh. One is showing the element size .
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File Type: jpg Mesh _full.jpg (96.1 KB, 11 views)
File Type: jpg mesh with body sizing.jpg (89.1 KB, 8 views)
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Old   June 12, 2013, 14:59
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It seem's to be correct, perhap's verify your BC and other parametrs (turbulence intensity, ...)
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Old   June 12, 2013, 15:05
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Tanjina Afrin
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I used pressure inlet and outlet BC, turbulent intensity is 5%, epsilon and k are 1 and 1 respectively. ( I used smaller epsilon and k, but that also gave the another type of divergence error message ).

When I use steady time instead of transient, after 500 and 1500 run, the images looked like this. (Attached)
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File Type: jpg trial_steady_1500.jpg (47.8 KB, 5 views)
File Type: jpg trial5_steady_500.jpg (49.1 KB, 8 views)
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Old   June 12, 2013, 15:29
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Hi
In general it'.s adviced to set an velocity inlet and pressure outlet for best convergence
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Old   June 12, 2013, 15:47
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Tanjina Afrin
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I tried it that way also.... velocity was not converging.

Actually, I wanted to let the water enter from static reservoir into pipe and air will replace the empty place of reservoir. That's why I put pressure inlet. But it didn't give this type of result. Could you suggest me how can I model this type of flow?
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