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pascool November 16, 2012 13:42

Cyclic boundary conditions concerning channel with constant flow rate
 
Hi there,

I'm trying to simulate a ribbed 2D channel in fully developed flow, by applying cyclic boundary conditions in streamwise direction and using simpleFoam. The case shall be run at a given bulk Reynolds number so that the flow rate must be specified.

My blockMeshDict file looks as follows:

Code:

boundary
(
    inlet
    {
          type cyclic;
          neighbourPatch outlet;
          faces
          (
            (0 21 22 1)
            (1 22 23 2)
            (2 23 24 3)
            (3 24 25 4)
          );
    }

    outlet
    {
        type cyclic;
        neighbourPatch inlet;
        faces
        (
            (16 17 38 37)
            (17 18 39 38)
            (18 19 40 39)
            (19 20 41 40)
          );
    }

    wall1
    {
          type wall;
          faces
          (
            (21 0 8 29)
          );
    }
   
    wall2
    {
          type wall;
          faces
          (
            (26 27 6 5)
            (27 28 7 6)
            (28 29 8 7)
          );
    }
   
    wall3
    {
          type wall;
          faces
          (
            (26 5 13 34)
          );
    }

    wall4
    {
          type wall;
          faces
      (
            (13 14 35 34)
            (14 15 36 35)
            (15 16 37 36)
      );
    }

    wall5
    {
          type wall;
          faces
          (
            (4 25 33 12)
            (12 33 41 20)
          );
    }

    frontAndBack
    {
          type empty;
          faces
          (
            (0 1 9 8)
            (1 2 10 9)
            (2 3 11 10)
            (3 4 12 11)
            (5 6 14 13)
            (6 7 15 14)
            (7 8 16 15)
            (8 9 17 16)
            (9 10 18 17)
            (10 11 19 18)
            (11 12 20 19)
            (21 29 30 22)
            (22 30 31 23)
            (23 31 32 24)
            (24 32 33 25)
            (26 34 35 27)
            (27 35 36 28)
            (28 36 37 29)
            (29 37 38 30)
            (30 38 39 31)
            (31 39 40 32)
            (32 40 41 33)
          );
    }
);

I don't know how to specify the initial and BC? My first attempt for p and U was:

Code:

FoamFile
{
    version    2.0;
    format ascii;
    class volScalarField;
    object p;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

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

internalField uniform 0;

boundaryField {
    inlet
    {
        type cyclic;
    }

    outlet
    {
        type cyclic;
    }
    wall1
    { 
            type            zeroGradient;
    }
    wall2
    {
        type            zeroGradient;
    }
    wall3
    {
        type            zeroGradient;
    }
    wall4
    {
        type            zeroGradient;
    }
    wall5
    {
        type            zeroGradient;
    }
    frontAndBack
    {       
  type            empty;
    }
}

Code:

FoamFile
{
    version    2.0;
    format      ascii;
    class      volVectorField;
    object      U;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dimensions      [0 1 -1 0 0 0 0];

internalField  uniform (2.98 0 0);

boundaryField
{
    inlet
    {
        type            cyclic;
    }
    outlet
    {
        type            cyclic;
    }
    wall1
    {
        type            fixedValue;
        value          uniform (0 0 0);

    }
    wall2
    {
        type            fixedValue;
        value          uniform (0 0 0);
    }
    wall3
    {
        type            fixedValue;
        value          uniform (0 0 0);
    }
    wall4
    {
        type            fixedValue;
        value          uniform (0 0 0);
    }
    wall5
    {
      type            fixedValue;
        value          uniform (0 0 0);
    }
    frontAndBack
    {
        type            empty;
    }

Any help apprechiated!
Best regards,
Pascal

meindert November 16, 2012 14:04

Did you have a look at the channelFoam solver?

Regarding the initial conditions, I would suggest using the perturbU utility. It generates a perturbed laminar velocity field. You should be able to find more information about it on the forums.
The boundary conditions look fine, but be aware that imposing periodic boundary conditions will cause problems in the pressure field if you do not treat the pressure field in a special way (the channelFoam solver takes care of this).


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