[Lukas1]

Hello everyone,

I´m quite new to OpenFOAM and have a problem with rhoPimpleFoam.
The case is a 3D pipeline with a orifice and a vessel at the end of the pipeline. The excitation is a sinusoidal excitation of velocity (mean flow 10 m/s) with an amplitude of 10 m/s and a frequency of 40 Hz. The aim is to evaluate the pressure fluctuations. The pipeline is splitted in the middle to use symmetry (xyplanes are symmetry planes). (see model in geometry.jpg)
When I start the simulation it stops after about 0,1 s of simulation and there comes the error message which can be seen in error.jpg. The final residual rises to a very high value. Moreover there are strong fluctuations behind the orifice which not really makes sense (see fluctuations.jpg). The turbulence model I use ist k omega SST. The medium is air (atmospheric pressure at outlet).
I tried the exact same simulation with a mean flow of 5 m/s, an amplitude of 5 m/s and a frequency of 40 Hz. This simulation runs normally and gives reasonable results. Can someone maybe tell me why the simulation with rhoPimpleFoam works for 5 m/s mean flow velocity but not for 10 m/s?

0/U:

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

internalField   uniform (0 0 0);

boundaryField
{
    inlet
    {
		type			uniformFixedValue;
		uniformValue	sine;
		uniformValueCoeffs		
		{
			frequency	40;
			amplitude	10;
			scale 		(1 0 0);
                        level 		(10 0 0);
			t0  		0; 
		}
    }

    outlet
    {
        type            zeroGradient;
    }

	xyplane
    {
        type            symmetry;
    }

    wall
    {
        type            noSlip;
    }
	
	wallrefine
    {
        type            noSlip;
    }
	
	xyplanevessel
    {
        type            symmetry;
    }
	
	vessel
    {
        type            noSlip;
    }
}

0/p:

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

internalField   uniform 101325;

boundaryField
{
    inlet
    {
        type            zeroGradient;
    }

    outlet
    {
        type            fixedValue;
        value           uniform 101325;
    }

	xyplane
    {
        type            symmetry;
    }
	
    wall
    {
        type            zeroGradient;
    }
	
    wallrefine
    {
        type            zeroGradient;
    }
	
	xyplanevessel
    {
        type            symmetry;
    }
	
	vessel
    {
        type            zeroGradient;
    }
	
	#includeEtc "caseDicts/setConstraintTypes"
}

0/T:

dimensions      [0 0 0 1 0 0 0];

internalField   uniform 293;

boundaryField
{
	#includeEtc "caseDicts/setConstraintTypes"
	
    inlet
    {
        type            fixedValue;
        value           uniform 293;
    }

    outlet
    {
        type            zeroGradient;
    }

	xyplane
    {
        type            symmetry;
    }

    wall
    {
        type            zeroGradient;
    }
	
	wallrefine
    {
        type            zeroGradient;
    }
	
	xyplanevessel
    {
        type            symmetry;
    }
	
	vessel
    {
        type            zeroGradient;
    }
	
	#includeEtc "caseDicts/setConstraintTypes"
	
}

0/omega:

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

internalField   uniform 25.88;

boundaryField
{
    inlet
    {
        type            fixedValue;
        value           uniform 25.88;
    }

    outlet
    {
        type            zeroGradient;
    }

	xyplane
    {
        type            symmetry;
    }
	
    wall
    {
        type            omegaWallFunction;
        value           uniform 25.88;
    }

    wallrefine
    {
        type            omegaWallFunction;
        value           uniform 25.88;
    }
	
	xyplanevessel
    {
        type            symmetry;
    }
	
	vessel
    {
        type            omegaWallFunction;
        value           uniform 25.88;
    }
}

0/k:

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

internalField   uniform 0.375;

boundaryField
{
    inlet
    {
        type            fixedValue;
        value           uniform 0.375;
    }

    outlet
    {
        type            zeroGradient;
    }

	xyplane
    {
        type            symmetry;
    }
	
    wall
    {
        type            kqRWallFunction;
        value           uniform 0.375;
    }

    wallrefine
    {
        type            kqRWallFunction;
        value           uniform 0.375;
    }
	
	xyplanevessel
    {
        type            symmetry;
    }
	
	vessel
    {
        type            kqRWallFunction;
        value           uniform 0.375;
    }
	
}

0/nut:

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

internalField   uniform 0;

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

    outlet
    {
        type            calculated;
        value           uniform 0;
    }

	xyplane
    {
        type            symmetry;
    }
	
    wall
    {
        type            nutkWallFunction;
        value           uniform 0;
    }

    wallrefine
    {
        type            nutkWallFunction;
        value           uniform 0;
    }
	
	xyplanevessel
    {
        type            symmetry;
    }
	
	vessel
    {
        type            nutkWallFunction;
        value           uniform 0;
    }
}

controlDict:

application     rhoPimpleFoam;

startFrom       latestTime;

startTime       0;

stopAt          endTime;

endTime         1;

deltaT          0.0001;

writeControl    adjustable;

writeInterval   0.002;

purgeWrite      0;

writeFormat     ascii;

writePrecision  6;

writeCompression off;

timeFormat      general;

timePrecision   6;

runTimeModifiable yes;

adjustTimeStep  yes;

maxCo           5;

fvSchemes:

ddtSchemes
{
    default         Euler;
}

gradSchemes
{
    default         Gauss linear;
}

divSchemes
{
    default         none;

    div(phi,U)       Gauss upwind;
    
    div(phi,k)       Gauss upwind;
    div(phi,omega)   Gauss upwind;
    div(phi,nuTilda) Gauss upwind;
    div(phi,R)       Gauss upwind;
    div(R)           Gauss linear;

    div(phi,e)      Gauss upwind;
    div(phi,K)      Gauss upwind;
    div(phi,Ekp)    Gauss upwind;

    div(phiv,p)     Gauss upwind;
    div((phi|interpolate(rho)),p)  Gauss upwind;

    div(((rho*nuEff)*dev2(T(grad(U)))))    Gauss linear;
}

laplacianSchemes
{
    default         Gauss linear corrected;
}

interpolationSchemes
{
    default         linear;
}

snGradSchemes
{
    default         corrected;
}

wallDist
{
    method          meshWave;
}

fvSolution:

solvers
{
    "pcorr.*"
    {
        solver          GAMG;
        tolerance       1e-2;
        relTol             0;
        smoother        DICGaussSeidel;
        cacheAgglomeration no;
        maxIter         50;
    }
	
	p
    {
        $pcorr;
        tolerance        1e-6;
        relTol           0.01;
    }

    pFinal
    {
        $pcorr;
        tolerance        1e-6;
        relTol           0;
    }

    "(U|k|omega|R|nuTilda|e|rho)"
    {
        solver          smoothSolver;
        smoother        symGaussSeidel;
        tolerance       1e-06;
        relTol          0.1;
    }

    "(U|k|omega|R|nuTilda|e|rho)Final"
    {
        $U;
        relTol          0;
    }
}

PIMPLE
{
    nNonOrthogonalCorrectors 1;
    nCorrectors         2;
}

Thanks for your help!

Lukas

[Swirl]

Hi,

from what you posted, I can see two things you may try.

1) reduce the maxmimum Courant number in your controlDict. rhoPimpleFoam does work with values larger than 1, but in any case it is a good idea to keep them below 1.

2) Try to use a waveTransmissive BC for the pressure field at your outlet. Since you are actively trying to generate pressure fluctuations, the fixed value BC at the outlet could be a problem. There is an explanation of how to use it under the link below.

https://openfoamwiki.net/index.php/H...dary_condition


Please let me know if this works.

[dlahaye]

Agree to waveTransmissive BC.

We succesfully applied them in https://www.mdpi.com/2311-5521/7/6/205

I am interested in seeing how it works for you.

[Lukas1]

Originally Posted by Swirl

Hi,

from what you posted, I can see two things you may try.

1) reduce the maxmimum Courant number in your controlDict. rhoPimpleFoam does work with values larger than 1, but in any case it is a good idea to keep them below 1.

2) Try to use a waveTransmissive BC for the pressure field at your outlet. Since you are actively trying to generate pressure fluctuations, the fixed value BC at the outlet could be a problem. There is an explanation of how to use it under the link below.

https://openfoamwiki.net/index.php/H...dary_condition


Please let me know if this works.

Thank you! I reduced the maxCo to 1 and now the simulation works!