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Problem with Acoustic Pulse Simulation

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Old   November 6, 2016, 04:40
Question Problem with Acoustic Pulse Simulation
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Weng-Ji Chen
Join Date: Sep 2016
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Hi, I want to test sound wave simulation solver, therefore I make a single acoustic pulse with groovyBC and have the viscosity term zero.

My solver is rhoCentralFoam and the faces except for inlet and outlet are cyclic. Outlet is wave transmissive.
In the first case, the distance between the inlet and the outlet is about 3 times the width of acoustic pulse. It seems to be good. The pulse can propagate from the inlet to the outlet and remain the waveform.
However, when I elongate my chamber size, that is, have the distance between the inlet and outlet be 30 times the width of pulse, the peak of the pulse begins to oscillate. It decays, grows, decays ... Obviously, something went wrong.

http://imgur.com/5tFGnyC
peak time evolution


I make sure the boundary conditions, time step and the mesh size are the same. Here are my boundary conditions:
Code:
/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  v1606+                                |
|   \\  /    A nd           | Web:      www.OpenFOAM.com                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       volScalarField;
    object      p;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

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

internalField   uniform 1e5;

boundaryField
{
    inlet1
    {
       type            zeroGradient;
    }


    outlet
    {
        type            waveTransmissive;
        phi             phi;
        psi             thermo:psi;
        rho             rho;
        gamma           1.3;
        fieldInf        1e5;
        lInf            50;
        value           $internalField;
    }

    right
    {
        type            cyclic;
    }

    left
    {
        type            cyclic;
    }

    up
    {
        type            cyclic;
    }
   down
    {
        type            cyclic;
    }

}

// ************************************************************************* //
Code:
/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  v1606+                                |
|   \\  /    A nd           | Web:      www.OpenFOAM.com                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       volVectorField;
    object      U;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

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

internalField   uniform (0 0 0);

boundaryField
{
    inlet1
    {
       type           groovyBC;
       valueExpression "vector(10*pow(e,-(time()-0.00017)*(time()-0.00017)/0.000000002),0,0)";
        variables "e=2.7182;"
      //omega=2*pi/0.00004;";
       timelines ();
       value uniform (0 0 0);  
     }


    outlet
    {
        type            pressureInletOutletVelocity;
        inletValue      uniform (0 0 0);
        value           uniform (0 0 0);
    }

    right
    {
        type            cyclic;
    }

    left
    {
        type            cyclic;
    }

    up
    {
        type            cyclic;
    }

 down
    {
        type            cyclic;
    }

}

// ************************************************************************* //
Code:
/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  v1606+                                |
|   \\  /    A nd           | Web:      www.OpenFOAM.com                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       volScalarField;
    object      T;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dimensions      [0 0 0 1 0 0 0];

internalField   uniform 300;

boundaryField
{
    inlet1
    {
        type            fixedValue;
        value           uniform 300;
    }



    outlet
    {
        type            inletOutlet;
        inletValue      uniform 300;
        value           uniform 300;
    }

    right
    {
        type            cyclic;
    }

    left
    {
        type            cyclic;
    }

    up
    {
        type            cyclic;
    }

    down
    {
        type            cyclic;
    }

}

// ************************************************************************* //
Code:
/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  v1606+                                |
|   \\  /    A nd           | Web:      www.OpenFOAM.com                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    location    "constant";
    object      thermophysicalProperties;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

thermoType
{
    type            hePsiThermo;
    mixture         pureMixture;
    transport       const;
    thermo          hConst;
    equationOfState perfectGas;
    specie          specie;
    energy          sensibleInternalEnergy;
}

mixture
{
    // normalised gas
    specie
    {
        nMoles      1;
        molWeight   28.96;
    }
    thermodynamics
    {
        Cp          1004.5;
        Hf          2.544e+06;
    }
    transport
    {
        mu          0;
        Pr          1;
    }
}


// ************************************************************************* //
Code:
/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  v1606+                                |
|   \\  /    A nd           | Web:      www.OpenFOAM.com                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    object      blockMeshDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

convertToMeters 0.001;

vertices
(
    (0 0 0)
    (2004 0  0)
    (2004 1 0)
    (0 1 0)  
    (0 0 1)
    (2004 0 1)
    (2004 1 1)
    (0 1 1)
);

blocks
(
     hex (0 1 2 3 4 5 6 7) (2004 1 1) simpleGrading (1 1 1)
     
);

edges
(
);

boundary
(
    inlet1
    {
        type patch;
        faces
        (
            (0 4 7 3)
        );
    }

    outlet
    {
        type patch;
        faces
        (
           (1 2 6 5)
         );
    }
    right
    {
        type  cyclic;
        neighbourPatch left;
        faces
        (
            (2 3 7 6)
        );
    }
    left
    {
        type cyclic;
        neighbourPatch right;
        faces
        (
            (0 1 5 4)
         );
    }
    up
    {
       type cyclic;
       neighbourPatch down;
       faces
       (
           (4 5 6 7)
       );
    }
    down
    {
       type cyclic;
       neighbourPatch up;
       faces
       (
           (0 1 2 3)
       );
    }
);

mergePatchPairs
(
);

// ************************************************************************* //
Besides, I tried sinusoidal wave. It went well, then I elongated the chamber and the same problem occurred.
Any advises will be helpful, thank you.

Last edited by Weng-Ji; November 6, 2016 at 22:07.
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