[JasonG]

I have been looking at pressure drops for internally bounded, steady-state, incompressible fluid flow cases with the simpleFoam solver. Typically, I specify a velocity at the entrance to the fluid domain and a reference pressure of 0 at the exit of the fluid domain.

A new case I am working on requires me to specify a velocity at the exit and a reference pressure at the entrance. I have been able to successfully do this with laminar assumptions, but as soon as I attempt to switch to the kOmegaSST turbulence solver I run into convergence issues. It appears the kinetic turbulence values become discontinuous near the entrance.

Any help and/or recommendations are greatly appreciated. Below are the current BC's I am implementing:

"intialConditions"

flowVelocity         (0 0 165.760612715333);
pressure             0;
turbulentKE          194.091657099187;
turbulentOmega       1731.03910939215;
kinematicvis         nu [ 0 2 -1 0 0 0 0 ] 0.0398447454916618;   // in^2/s
density             0.00007839;           //  Value of the density(sslug/in^3) pstatic = lbf/in^2 

//RAS PROPERTIES

RAS_MODEL         kOmegaSST; //kOmegaSST;    //laminar;
turb_on_off         on;    //on


#inputMode           merge

"p"

#include        "initialConditions"

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

internalField   uniform $pressure;

boundaryField
{
 
    outlet_1          
    {
        type            inletOutlet;
        inletValue      $internalField;
        value           $internalField;
    }



    inlet_1      
      {
        type            fixedValue;
        value           $internalField;
    }
   

    boundary       
    {
        type            zeroGradient;
    }

    symmetry      
    {
        type        symmetryPlane;
    }


}

"u"

#include        "initialConditions"

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

internalField   uniform (0 0 0);

boundaryField
{
    outlet_1   
    {
        type            outletInlet;
        outletValue     $flowVelocity;
        value           $flowVelocity;
    }




    inlet_1        
    {
        type            outletInlet;
        outletValue     $internalField;
        value           $internalField;
    }



    boundary       
    {
        type            fixedValue;
        value           $internalField;
    }

    symmetry       
    {
        type        symmetryPlane;
    }


}

"k"

#include        "initialConditions"

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

internalField   uniform $turbulentKE;

boundaryField
{

    outlet_1
    {
       type  fixedValue;
       value $internalField;
    }



    inlet_1
    {
        type            outletInlet;
        outletValue     $internalField;
        value           $internalField;
    }



    
    boundary
    {
        type            kqRWallFunction;
        value           $internalField;
    }

    symmetry       
    {
        type        symmetryPlane;
    }

}

"nut"

dimensions      [0 2 -1 0 0 0 0];

internalField   uniform 0;

boundaryField
{
    inlet_1
    {
        type            calculated;
        value           uniform 0;
    }



    outlet_1
    {
        type            calculated;
        value           uniform 0;
    }



  
     boundary
    {
        type            nutLowReWallFunction;
        value           uniform 0;
    } 



    symmetry       
    {
        type        symmetryPlane;
    }
}

"omega"

 
#include        "initialConditions"

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

internalField   uniform $turbulentOmega;

boundaryField
{


    outlet_1
    {
       type  fixedValue;
       value $internalField;
    }



    inlet_1
    {
        type            outletInlet;
        outletValue     $internalField;
        value           $internalField;
    }



    boundary
    {
        type            omegaWallFunction;
        value           $internalField;
    }



    symmetry       
    {
        type        symmetryPlane;
    }

}

[jherb]

You might try the fixedMean boundary condition for the velocity, k and omega at the outlet (assuming the the specified flow is going "outwards").
Then you do not enforce a constant value over the whole outlet but just the (area averaged) mean for the three quantities. So the turbulent block profile within your flow domain is not destroyed at the outlet.