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convergence problems with simpleFoam

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Old   August 1, 2013, 07:34
Default convergence problems with simpleFoam
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Vishal
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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.

0.zip

system.zip

constant.zip
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Old   August 1, 2013, 09:28
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Stefan Gaerling
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Hey there,

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

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

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

Cheers
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Old   August 1, 2013, 10:19
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Oh my bad. Thanks for pointing out the mistake. I will try to rectify and run the simulation again. Thanks again
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Old   August 2, 2013, 04:29
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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
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Old   August 2, 2013, 05:43
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Stefan Gaerling
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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.
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Old   August 2, 2013, 05:45
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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.

please post your terminal content after some iterations.
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Old   August 2, 2013, 06:00
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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.
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Old   August 2, 2013, 06:02
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U.jpg

Just check the above image.
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Old   August 2, 2013, 07:36
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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.

2D_pipe_flow_pres_induced.zip
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