CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > OpenFOAM > OpenFOAM Running, Solving & CFD

Boundary conditions: Asymmetric plane diffuser, k-omega SST, low-Re

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   September 13, 2012, 12:57
Default Boundary conditions: Asymmetric plane diffuser, k-omega SST, low-Re
  #1
New Member
 
Christian
Join Date: Jan 2011
Posts: 5
Rep Power: 15
Krischan is on a distinguished road
Hey everyone,
I'm trying to simulate the flow through an asymmetric plane diffuser (ERCOFTAC Testcase) to compare the results from the simulation against the experimental results as well as results obtained from a simulation with Ansys CFX.
I'm using k-omega SST as turbulence model together with a low Re-mesh in OF 2.1.1.
However, simulation results aren't as expected, as the flow separation is largely overpredicted, so I was wondering if I got the boundary conditions right for this kind of simulation (especially for k, omega and nut). Choosing the settings gave me a hard time, maybe there's still something wrong with it.

The contents of the files is posted below, any help is much appreciated.

Thanks in advance,
Krischan

k:
Code:
#include        "include/initialConditions"

dimensions      [0 2 -2 0 0 0 0];

internalField   uniform $turbulentKE;

boundaryField
{

    WALLUP
    {
        type fixedValue;
        value uniform 1e-11;
    }

    WALLD
    {
        type fixedValue;
        value uniform 1e-11;
    }
    OUTLET
    {
      type zeroGradient;
    }
    INLET
    {
        type            turbulentIntensityKineticEnergyInlet;
        intensity       0.05;
        U               U;
        phi             phi;
        value           uniform 0.05;
    }
    
    #include    "include/symPlanes"
}
omega:
Code:
#include        "include/initialConditions"

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

internalField   uniform $turbulentOmega;

boundaryField
{
    WALLUP
    {
        type            fixedValue;
        value             uniform 1e09;
    }
    WALLD
    {
        type            fixedValue;
        value             uniform 1e09;
    }
    OUTLET
    {
        type            zeroGradient;
    }
    INLET
    {
        type            fixedValue;
        value           $internalField;
    }
    
    #include    "include/symPlanes"    
}
nut:
Code:
dimensions      [0 2 -1 0 0 0 0];

internalField   uniform 0;

boundaryField
{
    INLET
    {
        type            calculated;
        value           uniform 0;
    }
    OUTLET
    {
        type            zeroGradient;
    }
    WALLUP
    {
        type            nutLowReWallFunction; 
        value           uniform 0;
    }
    WALLD
    {
        type            nutLowReWallFunction;
        value           uniform 0;
    }
    #include    "include/symPlanes"
}
p:
Code:
#include        "include/initialConditions"

dimensions      [0 2 -2 0 0 0 0];

internalField   uniform $pressure;

boundaryField
{
    INLET
    {
          type            zeroGradient;
    }

    OUTLET
    {    
        type            fixedValue;
        value            $internalField;
    }

    WALLD
    {
        type            zeroGradient;
    }

    WALLUP
    {
        type            zeroGradient;
    }

    #include    "include/symPlanes"
}
U:
Code:
#include        "include/initialConditions"

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

internalField   uniform $flowVelocity;

boundaryField
{
    INLET
    {
        type            fixedValue;
        value           uniform $flowVelocity;
    }

    OUTLET
    {
        type            zeroGradient;
    }


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

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

    #include    "include/symPlanes"    
}
initial conditions include file:
Code:
flowVelocity         (54.83 0 0);
pressure             0; //101325;
turbulentKE          11.2737;
turbulentOmega       72962;
#inputMode           merge

Last edited by Krischan; September 13, 2012 at 14:30.
Krischan is offline   Reply With Quote

Old   September 14, 2012, 08:45
Default
  #2
New Member
 
Christian
Join Date: Jan 2011
Posts: 5
Rep Power: 15
Krischan is on a distinguished road
Never mind - boundary conditions are correct, after changing the solver parameters in fvSolution (tolereance and reltol), everything works as expected.
Krischan is offline   Reply With Quote

Old   September 16, 2012, 18:17
Default
  #3
Senior Member
 
Join Date: Mar 2010
Posts: 172
Rep Power: 17
Jonathan is on a distinguished road
Hi Krischan,

glad you got your problem sorted! well done!

I just had a quick question regarding your set up! I see you need to use a wall function for nut even though you are using a low Re approach for k-omega ... i was wondering whether you knew why exactly you need to do this? i have seen this is the way you need to go, but still cant figure out why you need to use a WF at all if you are using a low Re implementation for the turbulence model and you have specified k / omega as per guidelines for a low Re implementation as you had done? Nut is a calculated from k / omega as we know, so why do we need a BC / wall function for it (nut) anyway?

many thanks for any help here!

cheers
Jonathan
Jonathan is offline   Reply With Quote

Reply

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
symmetry boundary conditions in cfx lost.identity CFX 41 May 22, 2013 08:21
inlet boundary conditions newOFuser OpenFOAM 1 January 10, 2013 09:08
Water subcooled boiling Attesz CFX 7 January 5, 2013 04:32
natural convection mehrdadeng CFX 10 February 25, 2011 06:25
Boundary conditions low Mach number flow lost.identity Main CFD Forum 0 November 28, 2010 05:44


All times are GMT -4. The time now is 03:25.