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Simulating pressure diffusion in OpenFoam

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Old   February 28, 2022, 06:21
Default Simulating pressure diffusion in OpenFoam
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Julia Fed
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Hi everyone,

I'm studying some simple cases to validate my own code. The initial set up is very simple: a large square of constant pressure with another square of higher pressure at the centre of the domain. Viscosity is very high (100) and the timestep very small (0.01). The goal is to observe pressure diffusion in time.

The whole domain is defined as porous in fvOptions.

I've been trying with pimpleFoam and a lot of different settings, but the result after any timestep > 0 is always a homogeneous pressure field, with the same value as the outer part of the domain. The high-pressure area disappears.

Does this make sense, or is it something that openFoam doesn't do...?
If you think I should be able to see pressure diffusion and I'm doing something wrong, I will post more details.

Thank you!
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Old   February 28, 2022, 16:58
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If you look at the description of pimpleFoam (e.g., you'll see that it says "Transient solver for incompressible, turbulent flow of Newtonian fluids, with ...". In an incompressible flow, the pressure field adjusts instantaneously to the velocity field, and that's why your initial pressure field disappears in the first timestep. So, you need a compressible solver like rhoPimpleFoam.

Secondly, and perhaps you have done this already, it's worth just doing some sums on the speed of sound and the physical dimensions of your pressurised zone to ensure that 0.01s is a fine enough resolution to capture all that you want to see. Good luck!
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Old   March 1, 2022, 04:29
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Thank you very much for your reply, that sounds right! I'll try it and let you know if it works
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openfoam, pimplefoam, pressure diffusion, transient

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