Flow through circular pipe not converging

Tanjina · June 12, 2013, 11:17

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.

ousegui · June 12, 2013, 14:21

Hi
your time step is small enough, so I advise you to improve your mesh

Tanjina · June 12, 2013, 14:29

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 ?

ousegui · June 12, 2013, 14:31

Can u send a picture of your meshing?

Tanjina · June 12, 2013, 14:40

Yea, off course. Please find the following images of mesh. One is showing the element size .

ousegui · June 12, 2013, 14:59

It seem's to be correct, perhap's verify your BC and other parametrs (turbulence intensity, ...)

Tanjina · June 12, 2013, 15:05

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)

ousegui · June 12, 2013, 15:29

Hi
In general it'.s adviced to set an velocity inlet and pressure outlet for best convergence

Tanjina · June 12, 2013, 15:47

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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June 12, 2013, 14:21		#2
ousegui New Member ousegui Join Date: Oct 2010 Posts: 19 Rep Power: 15	Hi your time step is small enough, so I advise you to improve your mesh

June 12, 2013, 14:29		#3
Tanjina Senior Member Tanjina Afrin Join Date: May 2013 Location: South Carolina Posts: 169 Rep Power: 12	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 ?

June 12, 2013, 14:31		#4
ousegui New Member ousegui Join Date: Oct 2010 Posts: 19 Rep Power: 15	Can u send a picture of your meshing?

June 12, 2013, 14:59		#6
ousegui New Member ousegui Join Date: Oct 2010 Posts: 19 Rep Power: 15	It seem's to be correct, perhap's verify your BC and other parametrs (turbulence intensity, ...)

June 12, 2013, 15:29		#8
ousegui New Member ousegui Join Date: Oct 2010 Posts: 19 Rep Power: 15	Hi In general it'.s adviced to set an velocity inlet and pressure outlet for best convergence

June 12, 2013, 15:47		#9
Tanjina Senior Member Tanjina Afrin Join Date: May 2013 Location: South Carolina Posts: 169 Rep Power: 12	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?