CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > OpenFOAM

about pEqn.H in bubbleFoam

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Display Modes
Old   May 17, 2011, 09:39
Default about pEqn.H in bubbleFoam
  #1
Member
 
Kai
Join Date: May 2010
Location: Stockholm
Posts: 40
Rep Power: 7
kaifu is on a distinguished road
Hi Foamers,

The boundary condition of p in the tutorials of bubbleColumn (bubbleFoam) may be wrong. From
@ 0/p
Code:
boundaryField
{
    inlet
    {
        type            zeroGradient;
    }

    outlet
    {
        type            fixedValue;
        value           uniform 0;
    }

    walls
    {
        type            buoyantPressure;
        value           uniform 0;
    }
}
@ constant/g
Code:
value           ( 0 -9.81 0 );
@ constant/polyMesh/blockMwshDict
Code:
...
vertices        
(
    (0 0 0)
    (0.15 0 0)
    (0.15 1 0)
    (0 1 0)
    (0 0 0.1)
    (0.15 0 0.1)
    (0.15 1 0.1)
    (0 1 0.1)
);
...

patches         
(
    patch inlet 
    (
        (1 5 4 0)
    )
    patch outlet 
    (
        (3 7 6 2)
    )
    wall walls 
    (
        (0 4 7 3)
        (2 6 5 1)
    )
);
we may know the gravity is in -y direction, and the inlet and outlet are in xz plane (normal to y axis) while wall normal to x axis. Apparently it is a vertical pipe. So how could the zeroGradient BC applied to inlet and the buoyantPressure applied to walls? In my opinion, inlet should be applied to buoyantPressure BC while walls zeroGradient BC.

Another issue comes from
@pEqn.H
Code:
pEqn.setReference(pRefCell, pRefValue);
the pRefCell and pRefValue were defined in createFields.H as
Code:
    label pRefCell = 0;
    scalar pRefValue = 0.0;
    setRefCell(p, mesh.solutionDict().subDict("PISO"), pRefCell, pRefValue);
what do pRefCell and pRefValue mean? Since p refers to the "reference pressure" in all kinds of CFD generally, why do we need a pRefValue here? Do we make a reference for pressure reference once more here? In my case, the pressure at outlet is fixed at 0.

On the other hand, if we designate 0 for pRefCell, (it is no problem with serial computation), when it comes to parallel computation, will it be problem dependent? So far i have modified the bubbleFoam solver to my case, it works well with serial computation. But in the parallel computation, it shows,
Quote:
GAMG: Solving for p, Initial residual = 0.0382384, Final residual = 9.98777e-11, No Iterations 767
in which the No Iterations is almost 30 times as it is in serial computation...

BTW i am using openfoam171.

// Kai

Last edited by kaifu; May 17, 2011 at 09:55.
kaifu is offline   Reply With Quote

Old   September 12, 2013, 00:16
Default
  #2
Senior Member
 
Join Date: Sep 2013
Location: Bangalore India
Posts: 134
Rep Power: 3
sam.ho is on a distinguished road
Hallo Foamers

I have the same problem and i would like to know the meaning of "pEqn.setReference(pRefCell, pRefValue);".

Could you please explain this line ?

Thanks a lot for your support
sam.ho is offline   Reply With Quote

Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
about bounded alpha equation for bubbleFoam and twoPhaseEulerFoam kaifu OpenFOAM 2 May 6, 2011 05:33
using bubbleFOAM to model a sludge digester tank Franz_J OpenFOAM Running, Solving & CFD 1 September 30, 2010 22:09
Inputs for bubbleFoam rans2009 OpenFOAM 0 October 8, 2009 07:59
bubbleFoam rans2009 OpenFOAM 3 October 5, 2009 04:28
Lift force modeling in bubbleFoam holger_marschall OpenFOAM Running, Solving & CFD 2 December 10, 2007 16:24


All times are GMT -4. The time now is 06:56.