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chtMultiRegionFoam steady vs unsteady

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Old   September 22, 2022, 12:36
Default chtMultiRegionFoam steady vs unsteady
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Joao Coelho
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Hi,

I am trying to check if using the steady version of chtMultiRegionFoam would be accurate enough to reach my solution. The case is a cooling channel, with an inlet and outlet, with solid walls all over. In one of the external boundaries of the solid wall (let's call it Wall_Gas), a temperature distribution is imposed, and the heat flux is computed during the simulation.

I have attached the average pressure in the Inlet patch at each timestep (steady simulation) and along the physical time (unsteady), and the average heat flux in the Wall_Gas boundary. The residuals are also shown.

unsteady_steady.zip


The unsteady simulation was started from the results of the steady simulations.

Even though the heat flux seems to not have any significant changes during the unsteady simulation (not only the average value but also the spatial distribution), the inlet pressure has a significant change, resulting in oscillations that tend to converge to a different final result (83.3 bar vs 80 bar) in each simulation.

Does anyone have any idea why this happens?

I have also attached the different folders "system" for each case.

Thanks in advance

system_unsteady.zip

system_steady.zip
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Old   September 22, 2022, 13:47
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Kumaresh
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Do pressure changes aggravate your problem?
Could you please elaborate on the significance of this thread.
Thank you*
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Old   September 23, 2022, 05:23
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Joao Coelho
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Quote:
Originally Posted by Kummi View Post
Do pressure changes aggravate your problem?
Could you please elaborate on the significance of this thread.
Thank you*
Since there are two different inlet pressures computed from those two different methods, I don't know which one of them is "more accurate" (and why). That was the main goal of this thread: Find a reason behind these two different results since the problem is exactly the same. I would expect the same results (or simply slightly different).

Does it make sense?


EDIT: I am not sure if I was clear in this so I will try to explain it better: I impose the outlet pressure and the inlet mass flow rate. Thus, the inlet pressure comes as a result of the simulation.

Last edited by jcoelho5; September 23, 2022 at 12:45. Reason: added more info
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