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Old   December 10, 2012, 06:20
Default Emptying Tank simpleFoam
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Claus Meister
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Hello Foamers,

has anybody ever done a simulation of emptying a tank using simpleFoam. My intention is to simulate a stationary single phase flow of tank draining with the goal to predict the mass flow rate. Can I do it and what I have to considered in order to get the simulation going?

Cheers in advance
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Old   December 10, 2012, 14:06
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Wouter van der Meer
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Hello Idrama,
Do you use a moving boundary for this simpleFoam simulation? Because were the fluid goes away something else must come in its place. So I think you need a two phase solver, or a moving boundary solver. But I am in no way an expert. The draining of a tank is not a stationary process. Another possibility; if you only want the flow through the outlet, you must create an equal flow through an inlet.


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Old   December 10, 2012, 16:11
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I know the leaving fluid must be replaced, but I consider the case when the water level does not change. Currently, I do the following issue, I set for the U field at the inlet and outlet zeroGradient. Pressure at the inlet is also set zeroGradient and at the outlet the bc is set to fixedValue uniform 0. I modified the simpleFoam-Solver by gravity. The simulations converge, but I don't know, if the result is correct or rather is my approach correct.

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Old   December 10, 2012, 17:23
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Wouter van der Meer
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Hello,
You probably know this too, but you can calculate the flow through an orifice with:
flow=C*A*sqrt(2*(press_inside - press_outside)/rhol)

Where A is surface area of orifice and C a constant depending on the shape of the orifice, for a first estimate C=1 will do.

Hope this helps a bit. I do not yet know enough of OpenFoam to help you with the other part.

Wouter
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Old   December 10, 2012, 21:45
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Hi

If you think a little about it emptying of a tank is purely driven by gravity.
If no gravity no pressure difference between inlet and outlet.

You need a solver that includes the gravity otherwise you will not get the correct pressure.
Or estimate the hydro-static pressure difference between inlet and outlet and just use the formula by Wouter.

Its pretty easy to set up a simulation of this using interFoam and just don't include the air phase.
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Old   December 11, 2012, 06:06
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@linnemann: I have implemented the gravity in simpleFoam by extending the Ueqn.H. Then I ran the simulation using the BC as described above. My problem is, was this approach correct - in an approximative manner of course.

I know that I have to taken two phase into account, but interFoam solver takes too much time. I need fast results of stationary tank drainages.

I also experimented with LTSInterFoam, but I haven't gotten any convergences up to now.

Cheers
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Old   May 10, 2013, 03:38
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Quote:
Originally Posted by idrama View Post
@linnemann: I have implemented the gravity in simpleFoam by extending the Ueqn.H. Then I ran the simulation using the BC as described above. My problem is, was this approach correct - in an approximative manner of course.

I know that I have to taken two phase into account, but interFoam solver takes too much time. I need fast results of stationary tank drainages.

I also experimented with LTSInterFoam, but I haven't gotten any convergences up to now.

Cheers
Hi idrama.
Sorry to hajack your thread!But I think our goal is the same.interFoam use much time to calculate the twophase interface.and I use LTSInterFoam too can did not get congergance!!So I want to use simpleFoam too or just use it to generate the iniitial fields.But you can see in this thread.
3Dmixer on simpleFoam and MRFInterFoam. the different solvers I get the different velocity field.But both of them get to convergence.In the last I think its caused by my B.C. and "without gravity in simpleFoam".
But I am not sure of this.Do you think if I add gravity in to simpleFoam I can get a much better velocity field?Thanks in advance!
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