# Pressure driven flow in vertical pipe

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September 3, 2013, 04:00
Pressure driven flow in vertical pipe
#1
Member

Hale
Join Date: May 2013
Posts: 53
Rep Power: 4
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.
Attached Images
 boundaryCondition.jpg (19.7 KB, 33 views)

 September 4, 2013, 13:47 #2 Senior Member   Nima Sam Join Date: Sep 2009 Location: Tehran, Iran Posts: 1,123 Blog Entries: 1 Rep Power: 14 well whats your OpenFOAM version ? __________________ Training Course on OpenFOAM at (http://www.isme.ir/) My Weblog (http://openfoam.blogfa.com/)

 September 4, 2013, 17:44 #3 Member   Hale Join Date: May 2013 Posts: 53 Rep Power: 4 It's version 2.0.1

 September 5, 2013, 00:53 #4 Senior Member   Nima Sam Join Date: Sep 2009 Location: Tehran, Iran Posts: 1,123 Blog Entries: 1 Rep Power: 14 then you should assign p_rgh not p! p will be calculated then through solving problem whats your p_rgh configurations? __________________ Training Course on OpenFOAM at (http://www.isme.ir/) My Weblog (http://openfoam.blogfa.com/)

September 5, 2013, 04:15
#5
Member

Hale
Join Date: May 2013
Posts: 53
Rep Power: 4
Quote:
 Originally Posted by nimasam 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

September 5, 2013, 09:17
#6
Senior Member

Nima Sam
Join Date: Sep 2009
Location: Tehran, Iran
Posts: 1,123
Blog Entries: 1
Rep Power: 14
Quote:
 Originally Posted by Hale 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
__________________
Training Course on OpenFOAM at (http://www.isme.ir/)
My Weblog (http://openfoam.blogfa.com/)

 September 13, 2013, 08:16 #7 Member   Hale Join Date: May 2013 Posts: 53 Rep Power: 4 Thanks a lot Nima. I have solved the problem.

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