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how to drive cyclic channel flow by a given pressure gradient

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Old   June 6, 2022, 07:14
Question how to drive cyclic channel flow by a given pressure gradient
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Jiaolong Deng
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hi guys, I am now confused by this issues for a long period. If any good suggestions are arisen, I would appreciate that a lot. I'm using OpenFOAM 8 and the following is the detailed description of my case:

The geometry is a 1/4 pipe and the mesh is generated by SALOME. I'm using a modified chtMultiRegionFoam solver (just do not solving EEqn). The material of the pipe is air, the flow is x-direction. The inlet and outlet of the pipe is set as cyclic BC.

I have checked lots of similar posts carefully about how to drive the cyclic pipe flow, most of them just adopt the fvOption "meanVelocityForce" by giving a special Ubar for the whole computational domain, and an extra pressure gradient is used to adjust U to Ubar dynamically. However, in contrast, what I'd like to do is to set a given pressure gradient (pressure increase) in part of the pipe as driving source. The velocity is calculated and to the end the corresponding pressure loss equals to the given pressure increase, so that the steady-state can build.

To do that, I use fvOption "vectorCodedSource" to add my given pressure gradient in the UEqn as:
Code:
codeAddSup
#{
       vectorField& USource = eqn.source();
       USource += vector(1, 0, 0);
#};
This source term is only added to a special cellzone located in:
[IMG]<a href="https://sm.ms/image/kTM2efi64WolqUz" target="_blank"><img src="https://s2.loli.net/2022/06/06/kTM2efi64WolqUz.png" ></a>[/IMG]

The simulation result seems pretty bad , the inlet p_rgh gets divergence, and the internal velocity goes up to 1e5!!

So I decreased the given source term to less than 0.00001, but the simulated U keeps growing and looks like it will never get steady as I wished... So I have no idea how to correctly set this momentum source value.

By the way, since the pressure field only has gradient BC in my case, I set pRefValue to 0 in fvSolution. But the simulated p_rgh never close to 0 as I set.

Anyway, my main problems can be summarized as:
1) how to drive a cyclic channel flow by adding a given momentum source? does anyone ever succeeded for that?
2) why the simulated p does not follow the given pRefValue for such a case where only pressure gradient BC is used?
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Old   June 7, 2022, 05:52
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Lukas
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Hello djilliam,

The boundary condition »fixedJump« is usually used to create the pressure jump across cyclic patches. It is often used to "simulate" a pump or fan. Maybe this helps you.
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cyclic bc, prefvalue, pressure gradient force

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