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Fluid flow caused by initial pressure difference

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Old   December 23, 2010, 19:18
Default Fluid flow caused by initial pressure difference
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I need some help with a simulation I'm tyring to run, and I've hit a wall on my own.

I'm trying the created a device that is basically a tube, open on one end, with air inside it. The air in half the tube (the closed end) is initially at a give pressure, lower than atmospheric. The air in the other half is open to the atmosphere and at atmospheric pressure.

When the simulation runs, the pressure difference should cause a flow to occur untill the fluid within the tube is all at atmospheric conditions. I want to examine the pressure and velocity during this process.

I have created the geometry for the tube, the fluid in the bottom half (the low pressure fluid) and the fluid for the entire tube.

What I can't do, is figure out how to set the initial pressures. Once I do that, I think the program should do the rest.

Pease, if anyone can help, I would be very grateful.

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Old   December 24, 2010, 09:42
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The solution to your problem sounds as simple as an initialize --> patch values in Fluent.

In your tube, you have two regions: one which is at atmospheric, and one which is below atmospheric pressure. Assuming you're not concerned about the small hydrostatic pressure differences in the system (gravity). I'd suggest doing the following:

1) Initialize the whole geometry to the final pressure you want (atmospheric)
2) Then, patch the bottom-half zone (Solve --> Initialize --> Patch) with a lower pressure.

If the bottom-half is not a separate fluid zone, you'll need to mark the bottom-half region manually in Fluent, then patch the region you create.
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