[maliheh]

Hi everybody,

I try to model an open channel with smooth bed in OpenFOAM software by pimpleFOAM (LES) solver. I will be appreciated if you help me to model it properly. Actually, I modeled an open channel. Unfortunately, I think my model has some problems. The specifications of my model as follow:
long 2.5 m; width= height =0.2 m (channel)
mean velocity =0.21 m/s; water height= 0.045 m; size mesh 2*2*2 mm
B.C

(0/U)

atmosphere
{
        type            symmetry;
        
    }

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

   outlet
    {
        type            inletOutlet;
        inletValue      uniform (0 0 0);
        value           uniform (0.21 0 0);
    }

    inlet
    {
         type            fixedValue;
         value           uniform (0.21 0 0);
    }

    smooth
    {
        type            fixedValue;
        value           uniform (0 0 0);
    }
}
///////////////////////////////////////////////


(0/P)

boundaryField
{

atmosphere
{
        type            symmetry;
        
    }

    walls
    {
     
        type            fixedFluxPressure;
        value           uniform 0;
    }

   inlet
    {
     
          type           zeroGradient;
 
    }

    outlet
    {
     
           type           zeroGradient;       
    }

smooth
    {

        type            fixedFluxPressure;
        value           uniform 0;
       
    }
//////////////////////////////////////////////////////////


(0/K)

     atmosphere
      {
        type            symmetry;
        
    }
    inlet
    {
        type            fixedValue;
        value           uniform 0.000165;
    }
    outlet
    {
         type            inletOutlet;
        inletValue       uniform 0.000165;
        value            uniform 0.000165;
       
    }
    walls
    {
        type            fixedValue;
        value           uniform 0;

    }
  
  smooth
    {
      
         type            fixedValue;
         value           uniform 0;
    }
} 



//////////////////////////


controlDict


application     pimpleFoam;

startFrom      latestTime;

startTime       0;

stopAt          endTime;

endTime 600;

deltaT          0.001;

writeControl    timeStep;

writeInterval   200;

purgeWrite      0;

writeFormat     ascii;

writePrecision  6;

writeCompression off;

timeFormat      general;

timePrecision   6;

//runTimeModifiable   true;
adjustTimeStep    yes;
maxCo    0.5;

functions
{
    fieldAverage1
    {
        type            fieldAverage;
        functionObjectLibs ( "libfieldFunctionObjects.so" );
        enabled         true;
        outputControl   outputTime;

        fields
        (
            U
            {
                mean        on;
                prime2Mean  on;
                base        time;
            }

            p
            {
                mean        on;
                prime2Mean  on;
                base        time;
            }
        );
    }
}
/////////////////////////


((fvSchemes))




ddtSchemes
{
    default           Euler;
}

gradSchemes
{
    default         Gauss linear;
}

divSchemes
{
    default         none;
    div(phi,U)      Gauss linear;
    div(phi,k)      Gauss limitedLinear 1;
    div(phi,B)      Gauss limitedLinear 1;
    div(B)          Gauss linear;
    div(phi,nuTilda) Gauss limitedLinear 1;
    div((nuEff*dev(T(grad(U))))) Gauss linear;
}

laplacianSchemes
{
    default         Gauss linear corrected;
}

interpolationSchemes
{
    default         linear;
}

snGradSchemes
{
    default         corrected;
}

fluxRequired
{
    default         no;
    p               ;
}


//////////////////////////////


fvSolution



solvers
{
    p
    {
        solver          GAMG;
        tolerance       0;
        relTol          0.1;
        smoother        GaussSeidel;
        nPreSweeps      0;
        nPostSweeps     2;
        cacheAgglomeration true;
        nCellsInCoarsestLevel 10;
        agglomerator    faceAreaPair;
        mergeLevels     1;
    }

    pFinal
    {
        $p;
        smoother        DICGaussSeidel;
        tolerance       1e-06;
        relTol          0;
    }

    "(U|k)"
    {
        solver          smoothSolver;
        smoother        symGaussSeidel;
        tolerance       1e-05;
        relTol          0.1;
    }

    "(U|k)Final"
    {
        $U;
        tolerance       1e-05;
        relTol          0;
    }
}

PIMPLE
{
    nOuterCorrectors 1;
    nCorrectors     2;
    nNonOrthogonalCorrectors 0;
    pRefCell        1001;
    pRefValue       0;
}
///////////////////////////////

1. I entered initial velocity of flow equal with 0.21 m/s (as mean velocity) but mean velocity is increasing during the channel while you may know it should be constant. Would you help me to solve this problem?

2. I want to verify my model with results from a paper that the plotted figure is attached. Based on this figure my model is not in good agreement with results from paper. (I didn't consider air influence on my model. Do this difference between my model and paper is related to the air effect???-paper didn't mentioned about air effect-)


Thank you for your valuable time.


Tobi: Put all your content of the files into code tags! Please keep clearance!

[hulli]

from my little experience with the channel tutorial and looking at your profile I think you need to run that a bit longer so the profile will equilibrate ... I meant that you should try cyclic boundaries and let it run for a very long time until you will see turbulences... Then do a timeaverage and your profile should HOPEFULLY fit ... may be that helps ... Best H

[maliheh]

Originally Posted by hulli

from my little experience with the channel tutorial and looking at your profile I think you need to run that a bit longer so the profile will equilibrate ... I meant that you should try cyclic boundaries and let it run for a very long time until you will see turbulences... Then do a timeaverage and your profile should HOPEFULLY fit ... may be that helps ... Best H

Many thanks for your response.

Actually, the channel has been run about 600 sec. Does this run time is enough???
Do my file(0) and system file are correct? If it is possible for you, please check my files.
I appreciate you.

[hulli]

Hi,

Well I guess looking at the Profiles that you want to get a fully turbulent flow? Right ? As I mentioned I never did any two Phase flows with OF. But in oder to get turbulences and a locartitmic shaped profile as shown in your figure and done in the tutorial channel 3xx you have either to run the case for a very long time... or you Speed that up using the utilities boxturb or perturbU to generate some white noise that helps to get a fully turbulent flow. The development of turbulences is also denpendent on your resolution (check your Yplus) and the Dimensions of your domain. After the turbulences developed do that timeaveraging I mentioned above... Just check the forum in that issue there are million of posts on that... i hope that helps