[nawa]

Can anyone help me with the boundary conditions for my simple multiphase problem?

The problem is similar to the pressure difference flow of fluid from one tank (in my case, the inlet tank) to the bottom dome through a pipe, as shown in the picture. For my problem, what should be the inlet and outlet boundaries to avoid floating-point execution errors? All mesh tests are okay, so I suspect the issue lies solely with the boundary conditions.

It works perfectly well when I change the boundary conditions to zeroGradient for all. However, I must derive my inlet pressure and velocities based on the fluid flow driven by the pressure difference.

When I use the inletOutlet boundaries, it results in floating-point exceptions. I need the inlet and outlet sections to allow reverse flow as well.

Here are the case files for my scenario that run successfully but don't work with inletOutlet boundaries:

alpha files = I just pasted alpha.air file here but let me tell you all the boudaries are same for alpha.air slurry and gas and it is to reduce some spaces since it is getting long.

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  4.0                                   |
|   \\  /    A nd           | Web:      www.OpenFOAM.org                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       volScalarField;
    object      alpha.air;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dimensions      [0 0 0 0 0 0 0];//kg m s K mol A cd

internalField   uniform 0;
boundaryField
{
    inlet
    {
        type           inletOutlet;
	inletValue 	uniform 0;
	value 		uniform 0;
    }

    outlet
    {
        type           inletOutlet;
	inletValue 	uniform 0;
	value 		uniform 0;
    }

    walls
    {
        type            zeroGradient;
    }
    inlet_pipe
    {
        type            zeroGradient;
    }
	dome
    {
        type           zeroGradient;
    }
	gas_outlet
    {
        type           zeroGradient;
    }
}
// ************************************************************************* //

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  4.0                                   |
|   \\  /    A nd           | Web:      www.OpenFOAM.org                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       volScalarField;
    object      p_rgh;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dimensions      [1 -1 -2 0 0 0 0];//kg m s K mol A cd

internalField   uniform 0; 

boundaryField
{

inlet
    {
        type            	zeroGradient;
    }
	outlet
    {
        type            fixedValue;
			value 		uniform 0;
    }

    gas_outlet
    {
        type            zeroGradient;
    }

    walls
    {
        type            zeroGradient;
    }
    
    inlet_pipe
    {
        type            zeroGradient;
    }
	dome 
	{	
		type 			zeroGradient;
	}
}

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

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  4.0                                   |
|   \\  /    A nd           | Web:      www.OpenFOAM.org                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       volVectorField;
    location    "0";
    object      U;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dimensions      [0 1 -1 0 0 0 0];//kg m s K mol A cd

internalField   uniform (0 0 0);

boundaryField
{
    inlet
    {
        type            noSlip;
    }
	
   outlet
     {
        type            fixedValue;
		value 			uniform (0 0 0);
    }
    inlet_pipe
    {
        type            noSlip;
    }

    walls
    {
        type            noSlip;
    }
    
    gas_outlet
    {
        type            noSlip;
    }
	dome 
	{
		type 	noSlip;
	}
}


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

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  4.0                                   |
|   \\  /    A nd           | Web:      www.OpenFOAM.org                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    location    "constant";
    object      transportProperties;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

phases  
(
slurry
{
    transportModel powerLaw; 
    powerLawCoeffs
	{
		n    n [0 0 0 0 0 0 0] 0.467;
		k    k [0 2 -1 0 0 0 0] 1.052;
		nuMin    nuMin [ 0 2 -1 0 0 0 0 ] 0.07;
		nuMax    nuMax [ 0 2 -1 0 0 0 0 ] 0.29;
	}
	rho      [ 1 -3 0 0 0 0 0 ] 1000; 
}

gas
{
    transportModel  Newtonian;
    nu              [0 2 -1 0 0 0 0] 0.00001816;
    rho             [1 -3 0 0 0 0 0] 0.627;
}
air
{
    transportModel  Newtonian;
    nu              [0 2 -1 0 0 0 0] 0.00001655; 
    rho             [1 -3 0 0 0 0 0] 1.145; 
}
);
sigmas
(
	(slurry air) 0.071
	(slurry gas) 0.071
	(air gas)    0
);

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

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  4.0                                   |
|   \\  /    A nd           | Web:      www.OpenFOAM.org                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       uniformDimensionedVectorField;
    location    "constant";
    object      g;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dimensions      [0 1 -2 0 0 0 0];//kg m s K mol A cd
value           (0 0 -9.81);//gravitational accelertaion


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

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  4.0                                   |
|   \\  /    A nd           | Web:      www.OpenFOAM.org                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    location    "constant";
    object      turbulenceProperties;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

simulationType  laminar;//we assume the flow to be laminar


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

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  4.0                                   |
|   \\  /    A nd           | Web:      www.OpenFOAM.org                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    object      fvSchemes;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

ddtSchemes
{
    default         Euler;
}

gradSchemes
{
    default         Gauss linear;
    grad(U)         Gauss linear;
    grad(gamma)     Gauss linear;
}

divSchemes
{
    div(rhoPhi,U)   Gauss upwind;
    div(phi,alpha)  Gauss vanLeer;
    div(phirb,alpha) Gauss linear;
    div(((rho*nuEff)*dev2(T(grad(U))))) Gauss linear;
}

laplacianSchemes
{
    default         Gauss linear corrected;
}

interpolationSchemes
{
    default         linear;
}

snGradSchemes
{
    default         corrected;
}


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

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  4.0                                   |
|   \\  /    A nd           | Web:      www.OpenFOAM.org                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    object      fvSolution;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

solvers
{
    "alpha.*"
    {
        nAlphaSubCycles 4;
        cAlpha          1;
    }

    "pcorr.*"
    {
        solver          PCG;
        preconditioner
        {
            preconditioner  GAMG;
            tolerance       1e-05;
            relTol          0;
            smoother        GaussSeidel;
        }
        tolerance       1e-05;
        relTol          0;
        maxIter         100;
    }

    p_rgh
    {
        solver          GAMG;
        tolerance       1e-07;
        relTol          0.05;
        smoother        GaussSeidel;
    }

    p_rghFinal
    {
        solver          PCG;
        preconditioner
        {
            preconditioner  GAMG;
            tolerance       1e-07;
            relTol          0;
            nVcycles        2;
            smoother        GaussSeidel;
        }
        tolerance       1e-07;
        relTol          0;
        maxIter         20;
    }

    U
    {
        solver          smoothSolver;
        smoother        GaussSeidel;
        tolerance       1e-08;
        relTol          0.1;
        nSweeps         1;
    }

    UFinal
    {
        $U;
        tolerance       1e-08;
        relTol          0;
    }
}

PIMPLE
{
    nCorrectors     2;
    nNonOrthogonalCorrectors 0;
}

relaxationFactors
{
    equations
    {
        "U.*"           1;
    }
}


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

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  4.0                                   |
|   \\  /    A nd           | Web:      www.OpenFOAM.org                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    location    "system";
    object      setFieldsDict;
}

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

defaultFieldValues
(
    volScalarFieldValue alpha.air 1
	volScalarFieldValue alpha.slurry 0
	volScalarFieldValue alpha.gas 0
);
regions
(
	boxToCell
	{
        origin (0 0 0);
        box    (-2.5 -1.5 -0.975) (2.5 1.5 0.975);
        fieldValues
        (
            volScalarFieldValue alpha.slurry 1
            volScalarFieldValue alpha.gas 0
			volScalarFieldValue alpha.air 0
        );
    }
  boxToCell
	{
        origin (-2.3 0 1.65);
        box    (-2.8 -0.5 1.525) (-1.8 0.5 1.775);
        fieldValues
        (
            volScalarFieldValue alpha.slurry 1
            volScalarFieldValue alpha.gas 0
			volScalarFieldValue alpha.air 0
        );
    }
		boxToCell
	{
        origin (0 0 1.475);
        box    (-1.25 -1.25 0.975) (1.25 1.25 1.975);
        fieldValues
        (
            volScalarFieldValue alpha.slurry 0
            volScalarFieldValue alpha.gas 1
			volScalarFieldValue alpha.air 0
        );
    }	
);

I really appreciate your help ! THank you ! Happy Foaming

this is the previous thread that I have already explored but nohing seems to work

Inlet Boundary Condition for Open Channel type flow