[saifee]

I am running an incompressible laminar flow simulation with the pimpleFoam solver. It has two openings on one side (n1 and n2) and one on the other (n3). I have set up the pressure boundary conditions so that the flow is driven primarily by the pressure applied at n3. The flow should be changing direction halfway. Realistically, the total volume passing through an opening should be the same for the two flow direction. Yet, when I sum over the patch flow rates (postProcessing function) of the two flow directions and compare them, they are different. What could be the potential reason(s) for this phenomenon?

Following is the pressure boundary condition I set up:

/*--------------------------------*- C++ -*----------------------------------*\
  =========                 |
  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
   \\    /   O peration     | Website:  https://openfoam.org
    \\  /    A nd           | Version:  10
     \\/     M anipulation  |
\*---------------------------------------------------------------------------*/

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

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

internalField   uniform 0;

boundaryField
{
    n1
	{
		type            totalPressure;
		p0              uniform 0;  // Reference total pressure (e.g., atmospheric pressure in Pascals)
		U               U;               // Velocity field name
		phi             phi;             // Flux field name
		rho             none;            // Density, use 'none' for incompressible flow
		psi             none;            // Compressibility, use 'none' for incompressible flow
		gamma           1;               // For incompressible flow, use 1
	}

	n2
	{
		type            totalPressure;
		p0              uniform 0;  // Reference total pressure
		U               U;
		phi             phi;
		rho             none;
		psi             none;
		gamma           1;
	}


    n3
    {
		type		uniformTotalPressure;
	p0
	{
		type		sine;
		frequency	0.3333333333333333;
		amplitude	-50.0;
		level		0;
	}


    }
    walls
    {
        type            zeroGradient;
    }

    defaultFaces
    {
        type            empty;
    }

}

// ************************************************************************* //

and U boundary condition:

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  v2006                                 |
|   \\  /    A nd           | Website:  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
{
    n1
    {
	type 		pressureInletOutletVelocity;
	value		uniform (0 0 0);
    }
    
    n2
    {
	type 		pressureInletOutletVelocity;
	value		uniform (0 0 0);
    }

    n3
    {
	type		pressureInletOutletVelocity;
	value		uniform (0 0 0);
    }

    walls
    {
        type            noSlip;
    }

    defaultFaces
    {
        type            empty;
    }
}

// ************************************************************************* //