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insulated container divided into equal volumes by a partition

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Old   April 5, 2011, 11:20
Default insulated container divided into equal volumes by a partition
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Alain
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Hi,

my goal is to model the following problem:
A gas is confined to one side of a rigid, insulated container divided into equal volumes by a partition. The other side is initially evacuated. The partition is removed, and the gas expands to fill the entire container. Assuming ideal gas behavior, determine the final equilibrium pressure.

I tried two ways to do this: first using two domains of fluid with an fluid-fluid interface, then using cell expression language to do a global initialization for a single fluid domain. But my results until now have been unsuccessful.

Anybody knows how to simulate this kind of problem?

Last edited by Alain_aftch; April 10, 2011 at 23:32.
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Old   April 5, 2011, 16:27
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I guess the first question is why not just use the back of an envelope rather than a CFD solver! I assume you have your reasons?
Did you run this as steady-state? In steady-state mass is not going to get conversed during convergence, so I think you would need to run this as a transient case.
Unfortunately that would be difficult to converge due to the high mach numbers in the evacuated space. Perhaps there's an expert parameter for the steady state case - anybody?
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Old   April 5, 2011, 18:51
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There are no expert parameters which will help. Stumpy's comment is correct - sounds like a first year uni thermodynamics question which can be solved in a few minutes with the ideal gas laws.... So why bother with CFD?

It will be a tricky CFD simulation with all sorts of nasty initial transients.
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Old   April 6, 2011, 08:44
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Not sure if this would work, but if you set it up as a multiphase case with initial conditions set so the volume fraction of gas is 1, then you may be able to run steady-state. For steady-state multiphase cases in a closed system a global correction is applied to converse the mass of each phase.
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Old   April 10, 2011, 02:35
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Quote:
Originally Posted by stumpy View Post
Not sure if this would work, but if you set it up as a multiphase case with initial conditions set so the volume fraction of gas is 1, then you may be able to run steady-state. For steady-state multiphase cases in a closed system a global correction is applied to converse the mass of each phase.
the main idea is to simulate a burst disc
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Old   April 10, 2011, 02:40
Default something like that
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Quote:
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the main idea is to simulate a burst disc
e.g.:
http://www.drthfrank.de/publications...ensation_b.pdf
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Old   April 10, 2011, 06:49
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What are you trying to get out of the analysis? Your first post only mentioned the final pressure, but now you are talking about a burst disc.
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Old   April 10, 2011, 15:51
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What are you trying to get out of the analysis? Your first post only mentioned the final pressure, but now you are talking about a burst disc.
i'm trying to get the simulation of a pressure vessel failure and the release/dispersion of fluid into a low pressure chamber. Imagine that the fail is due to a burst disc. For this reason, I started this work with the first problem, which I know the theoretical answers.

Last edited by Alain_aftch; April 10, 2011 at 23:25.
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Old   April 10, 2011, 22:21
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I assume you mean the final steady state mixed result for the "first problem".

So is your question how can you make the opening suddenly appear?
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Old   April 10, 2011, 23:23
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I assume you mean the final steady state mixed result for the "first problem".

So is your question how can you make the opening suddenly appear?
thatīs the stuff
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Old   April 11, 2011, 06:28
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Lots of ways.

1) Define an initial condition with different conditions on each side. This is the easiest way.
2) Do a simulation to define the initial conditions where they are not connected (maybe a wall in the gap). Then use this as an initial condition on a simulation with the gap connected.
3) Put a source term, probably a momentum source, in the gap which initially stops flow (or at least greatly slows it down) and then dissappears.
4) Use a GGI and a sliding interface to slide it open.
5) Use moving mesh to open a connection up.

I could probably think of more if I could be bothered. But option 1 is simplest so go with that if it is suitable.
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