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Pressure driven flow in vertical pipe

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Old   September 3, 2013, 04:00
Default Pressure driven flow in vertical pipe
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Hale
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Hi to all,

I have a tank connected to a vertical pipe. The tank is full of water and the sides of the tank have the following boundary condition

Inlet
U: zeroGradient;
p: zeroGradient;
alpha1: fixedValue uniform 1;

The water in the tank would then fall into the vertical pipe. The outlet of the pipe has the following boundary condition

outlet
U: zeroGradient;
p: fixedValue uniform -250;
alpha1: zeroGradient;

The upper side of the tank is then open to the atmosphere with following boundary condition

atmosphere
U: inletOutlet;
p: totalPressure (p0=0);
alpha1: zeroGradient;

In this way I want the water to fall down based on the pressure difference between outlet and inlet. But with the mentioned boundary conditions the water moves upward and the simulation crashes after some seconds. I guess that the hydrostatic pressure at the outlet causes problems, since there is a positiv hydrostatic pressure corresponding to the water in the pipe.

Am I choosing wrong boundary conditions?

I really appreciate any help and idea.

NB. I'm using interFoam.
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Old   September 4, 2013, 13:47
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well whats your OpenFOAM version ?
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Old   September 4, 2013, 17:44
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It's version 2.0.1
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Old   September 5, 2013, 00:53
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then you should assign p_rgh not p! p will be calculated then through solving problem whats your p_rgh configurations?
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Old   September 5, 2013, 04:15
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Quote:
Originally Posted by nimasam View Post
then you should assign p_rgh not p! p will be calculated then through solving problem whats your p_rgh configurations?
Sorry I didn't write that in the discribtion but I am actually assigning p_rgh and not p.

By the way do you know how to change the values for Sp and Su. In the page below, post #7 decribes that the problem with unbounded alpha1 can be solved by changing Sp and Su but I have no idea how and where to change them. Do you know that?

http://www.cfd-online.com/Forums/ope...tml#post449990


Thanks for your time
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Old   September 5, 2013, 09:17
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Quote:
Originally Posted by Hale View Post
Sorry I didn't write that in the discribtion but I am actually assigning p_rgh and not p.
why do u assign p_rgh a negative value?
Quote:
By the way do you know how to change the values for Sp and Su. In the page below, post #7 decribes that the problem with unbounded alpha1 can be solved by changing Sp and Su but I have no idea how and where to change them. Do you know that?

http://www.cfd-online.com/Forums/ope...tml#post449990


Thanks for your time
well, you should change the source code, look at alphaEqn.H, in
Code:
solvers/multiphase/interFoam
and 
solvers/multiphase/compressibleInterFoam
then compile your code , however i think atleast now you should get sure about your BC it can be future step
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Old   September 13, 2013, 08:16
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Thanks a lot Nima. I have solved the problem.
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