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Pressure difference as an input to simpleFoam

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Old   August 29, 2021, 09:22
Question Pressure difference as an input to simpleFoam
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Ahmad Mahmoud
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I have a problem where I am required to simulate the flow through a reconstructed geometry of a human vessel (pipe flow), where the pressure at the inlet and at the outlet is known, in order to find the resultant flow rate.



My question is how should I set up a case in openFoam using the simpleFoam solver, where the pressures are the input and no velocity is specified. I have tried doing this by setting the velocity boundary condition to zero gradient at both ends, and the pressure as fixed value for both values, but the results were usually unstable and did not converge satisfactorily. I have tried with k-epsilon turbulence models as well as k-omega SST and even fully laminar, but none of them would converge.


What appropriate boundary conditions should I use and how can I improve the stability and convergence of the problem?


Thank in advance!
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Old   August 29, 2021, 21:00
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Francisco T
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That seems correct. Check the file attached, which is a microchannel (100microns x 20) the velocity is generated correctly with pressure. This case is laminar.

microch_vel.png
microchannel100x20Pressure.zip
Perhaps you can try laminar first and then add turbulence later?


What issues are you having?
Cheers
Francisco
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Old   August 31, 2021, 03:10
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Andreas P.
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Maybe you can try the pressureInletUniformVelocity instead of zeroGradient for one side. This sets velocity to a constant value over the whole inlet in one direction, which made simulations stable in my case...

https://www.openfoam.com/documentati...d.html#details
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Old   September 6, 2021, 06:52
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Ahmad Mahmoud
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Quote:
Originally Posted by AndreasPe View Post
Maybe you can try the pressureInletUniformVelocity instead of zeroGradient for one side. This sets velocity to a constant value over the whole inlet in one direction, which made simulations stable in my case...

https://www.openfoam.com/documentati...d.html#details

What value would I set i to. Note that I do not have vales for the velocity or the flux, that is the value i am after.
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Old   September 6, 2021, 07:04
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The "value" field ist just a dummy field for this boundary condition, that will be overwritten by the calculation of the boundary condition. So you can just set it to 0.
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Old   September 6, 2021, 12:21
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Another suggestion is to apply a total pressure boundary condition at the upstream end; the ESI documentation page (https://www.openfoam.com/documentati...tions-subsonic) suggests that this gives good stability ... my experience is a bit mixed though. Let us know what ends up working for you.
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Old   September 6, 2021, 13:44
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Domenico Lahaye
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Aha!

What has your experience with subsonic cases been?

I am working on a jet-in-co-flow with transonic jet to (hopefully) clarify convergence issues. What are in your experience are point to look into?

Would pressure-velocity coupled solver help in these cases?

Thx, Domenico.
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boundary condition, internal flow, pipe flow, simplefoam convergence, simplefoam pressure bc

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