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

Boundary Conditions of Phase Fractions (alpha-file)

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   January 22, 2015, 09:09
Default Boundary Conditions of Phase Fractions (alpha-file)
  #1
New Member
 
Join Date: Jan 2015
Posts: 1
Rep Power: 0
Truehnue is on a distinguished road
Hello everybody,

I am a very new user of OpenFoam and currently I have some trouble with these boundary conditions of phase fractions.
Currently, I am looking into the alpha-file that can be found in the 0-folder of the example multiphase/twoPhaseEulerFoam/bubbleColumn.
There, the following boundary conditions are defined:

Code:
boundaryField
{
    inlet
    {
        type            fixedValue;
        value           uniform 0.5;
    }
    outlet
    {
        type            inletOutlet;
        phi             phi.air;
        inletValue      uniform 1;
        value           uniform 1;
    }
    walls
    {
        type            zeroGradient;
    }
}
My question now is how to interpret the inletOulet boundary condition at the patch "outlet". The documentation states that U and p are switched between fixedValue and zeroGradient depending on direction of U.

For this example, U is the velocity of air (since we are in the alpha.air-file), right?

But why should the direction of velocity of the air change? Initially, it moves up with a velocity of 0.1 m/s (defined in U.air) and afterwards, the air should escape at the top of the column as well.

And what does "U and p are switched between fixedValue and zeroGradient" mean?

I am really looking forward for you answers. Thank you :-)

Greetings,
Katharina
Truehnue is offline   Reply With Quote

Old   February 8, 2015, 06:22
Default
  #2
Senior Member
 
Nima Samkhaniani
Join Date: Sep 2009
Location: Tehran, Iran
Posts: 1,264
Blog Entries: 1
Rep Power: 21
nimasam is on a distinguished road
Dear Katharina

this Bc works as:
1- for outflow similar zeroGradient
2- for inflow or in other word back flow like fixedValue
__________________
Telegram channel (https://telegram.me/openfoam4Iranian)
My Weblog in Persian(http://openfoam.blogfa.com/)
My Personal Website (http://nimasamkhaniani.ir/)
nimasam is offline   Reply With Quote

Old   December 2, 2016, 13:27
Default b.c. for closed block uniformly filled with a two-phase mixture
  #3
New Member
 
Nicoḷ Scapin
Join Date: Apr 2016
Posts: 15
Rep Power: 6
nic92 is on a distinguished road
Dear Foamers,
I'm experiencing some convegence problems for a closed box initially uniformly filled with a two-phase mixture. I am using twoPhaseEulerFoam 3.0.x.
Since there isn't inlet and outlet mass flow rate, I set for velocity:

dimensions [0 1 -1 0 0 0 0];

internalField uniform (0 0 0);

boundaryField

{

bodyWall
{
type fixedValue;
value uniform (0 0 0);
}

}

For pressure (p_rgh):
{

bodyWall
{
type fixedFluxPressure;
value $internalField;
}

}
Since there is not a patch with fixed pressure, I need to set it in pRefCell and pRefValue (fvSolution) the reference values. Even by doing so, the solver crashes after few time steps since the GAMG solver is not able to zero the residuals.

Courant Number mean: 0 max: 0
Max Ur Courant Number = 0
deltaT = 1.5e-06
Time = 1.5e-06

PIMPLE: iteration 1
MULES: Solving for alpha.air
alpha.air volume fraction = 0.2 Min(alpha.air) = 0.2 Max(alpha.air) = 0.2
MULES: Solving for alpha.air
alpha.air volume fraction = 0.2 Min(alpha.air) = 0.2 Max(alpha.air) = 0.2
MULES: Solving for alpha.air
alpha.air volume fraction = 0.2 Min(alpha.air) = 0.2 Max(alpha.air) = 0.2
Constructing momentum equations
min T.air 300
min T.water 350
GAMG: Solving for p_rgh, Initial residual = 1, Final residual = 0.000486295, No Iterations 1000
GAMG: Solving for p_rgh, Initial residual = 0.00374525, Final residual = 0.000509884, No Iterations 1000
PIMPLE: iteration 2
MULES: Solving for alpha.air
alpha.air volume fraction = 0.2 Min(alpha.air) = 0.2 Max(alpha.air) = 0.2
MULES: Solving for alpha.air
alpha.air volume fraction = 0.2 Min(alpha.air) = 0.2 Max(alpha.air) = 0.2
MULES: Solving for alpha.air
alpha.air volume fraction = 0.2 Min(alpha.air) = 0.2 Max(alpha.air) = 0.2
Constructing momentum equations
min T.air 225.521
min T.water 349.979
GAMG: Solving for p_rgh, Initial residual = 0.00374532, Final residual = 1.02015e+49, No Iterations 1000
GAMG: Solving for p_rgh, Initial residual = 1, Final residual = 9.65999e-07, No Iterations 54
PIMPLE: iteration 3
MULES: Solving for alpha.air
alpha.air volume fraction = 4.97724e+18 Min(alpha.air) = -1.10963e+35 Max(alpha.air) = 6.01367e+34
MULES: Solving for alpha.air
alpha.air volume fraction = 4.40872e+89 Min(alpha.air) = -9.57781e+105 Max(alpha.air) = 1.16947e+106
MULES: Solving for alpha.air
alpha.air volume fraction = -1.98169e+229 Min(alpha.air) = -8.59538e+246 Max(alpha.air) = 1.2115e+247
Constructing momentum equations
#0 Foam::error:rintStack(Foam::Ostream&) at ??:?
#1 Foam::sigFpe::sigHandler(int) at ??:?
#2 ? in "/lib/x86_64-linux-gnu/libc.so.6"
#3 Foam::tmp<Foam::GeometricField<double, Foam::fvPatchField, Foam::volMesh> > Foam::mag<Foam::Vector<double>, Foam::fvPatchField, Foam::volMesh>(Foam::tmp<Foam::GeometricField<Foam ::Vector<double>, Foam::fvPatchField, Foam::volMesh> > const&) at ??:?
#4 Foam::dragModels::segregated::K() const at ??:?
#5 Foam::BlendedInterfacialModel<Foam::dragModel>::K( ) const at ??:?
#6 Foam::twoPhaseSystem::Kd() const at ??:?
#7 ? at ??:?
#8 __libc_start_main in "/lib/x86_64-linux-gnu/libc.so.6"
#9 ? at ??:?
Floating point exception (core dumped)

I have also tried the PCG solver but the problem still remains (it is only postponed).

The strange aspect is that if I set a fixedValue for pressure in one the patch, I obtain a convergent solution. However, I would like to avoid this possibility since I am treating a strictly incompressible case and where I set a velocity I do not want to set a pressure.

I have attached the system directory.
Thanks for your feed-back.
Attached Files
File Type: gz system.tar.gz (1.9 KB, 4 views)
nic92 is offline   Reply With Quote

Reply

Tags
alpha, boundaries, inlet, outlet

Thread Tools Search this Thread
Search this Thread:

Advanced Search
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 Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Wind turbine simulation Saturn CFX 58 July 3, 2020 02:13
SparceImage v1.7.x Issue on MAC OS X rcarmi OpenFOAM Installation 4 August 14, 2014 07:42
An error has occurred in cfx5solve: volo87 CFX 5 June 14, 2013 18:44
[swak4Foam] funkySetFields compilation error tayo OpenFOAM Community Contributions 39 December 3, 2012 06:18
pisoFoam compiling error with OF 1.7.1 on MAC OSX Greg Givogue OpenFOAM Programming & Development 3 March 4, 2011 18:18


All times are GMT -4. The time now is 20:53.