CFD Online Discussion Forums - K-Omega-Epsilon BCs for suction inlet

Hello everyone. I have a question about RAS turbulence boundary conditions related to a suction inlet (i.e. uniform flow velocity out of the domain). While my k omega SST turbulence model converges, my k epsilon implementation blows up (though this might be because this isn't really a free shear layer problem). My y+ is uniform (for now) at about 20. After shadowing these forums extensively, it seemed that k omega SST with the omegaWallFunction, the nutUSpaldingWallFunction, the kqRWallFunction takes care of the wall boundary conditions.

My question is related to the suction inlet (which I hadn't thought of really). I have been using the usual CFD online tool (https://www.cfd-online.com/Tools/turbulence.php) to calculate my k, omega and epsilon assuming my turbulence length scale to be 0.07 the hydraulic diameter and specifying them through turbulentIntensityKineticEnergyInlet (for k), fixedValue (for omega), turbulentMixingLengthDissipationRateInlet (for epsilon).

However this link (https://www.openfoam.com/documentati...alarField.html) says "In the event of reverse flow, a zero-gradient condition is applied" for omega. Now technically in my suction inlet, a reverse flow IS happening. I'm at a loss here - what exactly do I specify for my inlet and outlet BCs for k, omega, epsilon. I have my boundary conditions added here.

U

Code:

internalField   uniform 10;



boundaryField

{

    walls

    {

                type            kqRWallFunction;

                value           $internalField;

    }



    outlets

    {

                type                         zeroGradient;

    }



    inlet

    {

                type                         turbulentIntensityKineticEnergyInlet;

                intensity               0.02;

                value                         uniform 0.00015;



    }

}

Code:

dimensions      [0 2 -2 0 0 0 0];



internalField   uniform 0;



boundaryField

{

    inlet

    {

        type            zeroGradient;

    }



    outlets

    {

        type            totalPressure;

        p0              uniform 0.0;

        gamma                0.0;

        value           $internalField;

    }



    walls

    {

        type            zeroGradient;

    }



}

nut

Code:

dimensions      [0 2 -1 0 0 0 0];



internalField   uniform 0.14;



boundaryField

{

    inlet

    {

        type            freestream;

        freestreamValue uniform 0.14;

    }



    outlets

    {

        type            freestream;

        freestreamValue uniform 0.14;

    }



    walls

    {

        type            nutUSpaldingWallFunction;

        value           uniform 0;

    }

}

Code:

dimensions      [0 2 -2 0 0 0 0];



internalField   uniform 10;



boundaryField

{

    walls

    {

                type            kqRWallFunction;

                value           $internalField;

    }



    outlets

    {

                type                         zeroGradient;

    }



    inlet

    {

                type                         turbulentIntensityKineticEnergyInlet;

                intensity               0.02;

                value                         uniform 0.00015;



    }

}

epsilon

Code:

dimensions      [0 2 -3 0 0 0 0];



internalField   uniform 100;



boundaryField

{

    walls

    {

                type            epsilonWallFunction;

                value                $internalField;

    }



    outlets

    {

                type                         zeroGradient;

    }



    inlet 

    { 

                type turbulentMixingLengthDissipationRateInlet; 

                mixingLength 0.0378; 

                value uniform 200; // placeholder 

    } 

}

omega

Code:

dimensions      [0 0 -1 0 0 0 0];



internalField   uniform 1000;



boundaryField

{

    walls

    {

        type            omegaWallFunction;

        Cmu             0.09;

        kappa           0.41;

        E               9.8;

        value           $internalField;

    }

    inlet

        {

            type                         fixedValue;

            value                            uniform 0.324;

        }

        outlets

        {

            type                         zeroGradient;

        }

}

Thanks for reading! If you need anymore information, feel free to ask.