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 inf.vish August 1, 2013 07:34

convergence problems with simpleFoam

3 Attachment(s)
Hi all,
I am trying to achieve a pressure driven steady state laminar flow of water through a pipe. (2D case). I am not able to achieve a convergence. But I solved the same case with velocity driven flow and the convergence reached in 105 iterations.
I am attaching my system directory as well as 0 directory.

looking forward to some solution.

Attachment 24014

Attachment 24015

Attachment 24016

 gillimaniac August 1, 2013 09:28

Hey there,

first of all in "constant" you define the kinematic viscosity nu = 858e-9 but the kinematic viscosity of water at 20°C is 1e-6 m²/s i believe.

Additionally your applied pressure difference between inlet and outlet is very low. It calculates to:

1e-4 m²/s² * 1000 kg/m³ = 0,1 kg/(m*s²) = 0,1 Pa.

Cheers

 inf.vish August 1, 2013 10:19

Oh my bad. Thanks for pointing out the mistake. I will try to rectify and run the simulation again. Thanks again

 inf.vish August 2, 2013 04:29

The solution still won't converge. Can you help. I changed the value of nu to 1e-06 and pressure to 1 m^2/s^2

 gillimaniac August 2, 2013 05:43

How does your case look after maybe 100 iterations?

Do you have perhaps inflow at your outlet?
In this case you can try using inletOutlet instead of zeroGradient for U @ outlet at first.

Perhaps you can plot your initial residuals and share the graph here.

 gillimaniac August 2, 2013 05:45

Okay i took your case files, changed the nu and p values and the case converged after 224 iterations so there should be no problem.

 inf.vish August 2, 2013 06:00

Yeah it converged after 224 iterations. You are absolutely correct about that. But did you look at the results? My results are very weird. The velocity distribution looks odd. It should have an entrance region and then gradually become parabolic.

 inf.vish August 2, 2013 06:02

1 Attachment(s)
Attachment 24047

Just check the above image.

 inf.vish August 2, 2013 07:36

1 Attachment(s)
Here is my test case again. Please tell me where am i going wrong. As far as i know the boundary conditions conform with those for Poiseuille flow. :confused::confused::confused:

Attachment 24052

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