[shouvik ghorui]

Hello, everyone, I am new in OpenFOAM, I am trying to simulate a negative pressure ventilation room.there is a present and a bed inside the room and the present release constant heat flux. for creating the negative pressure inside the room. I want to give an inlet and outlet as a pressure boundary condition. for inlet, I will give 0pa and for the outlet -8pa.
and I use buoyantPimpleFoam
now the question is
1) can I use both pressure boundary condition at inlet and outlet?
2) in which file(p or p_rgh) I have to specified value of pressure -8pa?
if any data is required to say then, please let me know. thanks in advance. if anyone helps me it will be great for me.

[HPE]

Hi,

>> 1) can I use both pressure boundary condition at inlet and outlet?

Yes, you can.

>> 2) in which file(p or p_rgh) I have to specified value of pressure -8pa?

If you will carry out incompressible flow simulation, specification in "p" should suffice. But, note that "p" is the kinematic pressure, and in units of "m2/s2", therefore, you need to do a unit conversion from "Pa".

Hope it helps.

BTW: I would set inlet 8Pa and outlet 0Pa (no specific reason).

[Tobi]

Just want to make one statement. Using a "negative pressure" needs the assumption of incompressible as only in this scenario we have only pressure gradients to look at. For compressible flows one has to take an EOS into account. Thus, a negative pressure will make trouble as we all know, there is no pressure value with a negative sign.

[shouvik ghorui]

Originally Posted by Tobi

Just want to make one statement. Using a "negative pressure" needs the assumption of incompressible as only in this scenario we have only pressure gradients to look at. For compressible flows one has to take an EOS into account. Thus, a negative pressure will make trouble as we all know, there is no pressure value with a negative sign.

thank you sir.

[shouvik ghorui]

Originally Posted by HPE

Hi,

>> 1) can I use both pressure boundary condition at inlet and outlet?

Yes, you can.

>> 2) in which file(p or p_rgh) I have to specified value of pressure -8pa?

If you will carry out incompressible flow simulation, specification in "p" should suffice. But, note that "p" is the kinematic pressure, and in units of "m2/s2", therefore, you need to do a unit conversion from "Pa".

Hope it helps.

BTW: I would set inlet 8Pa and outlet 0Pa (no specific reason).

thank you sir.

[Sakun]

Hi guys,


Sorry for messaging to an old thread

i am simulating a compressor blade and i need to required apply total pressure,static pressure for "p" and total temperature for "T" .

my simulation shows a tendency to converge but after around 2000 iterations it diverges and continue till end .


i attached p ,U codes and BC values, i would really appreciate if you could comment on them whether it is correct or wrong. i need desperately need help.


p file,

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  v2112                                 |
|   \\  /    A nd           | Website:  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 97251;

boundaryField
{
    INLET
    {

        //type            zeroGradient;

        //type            freestreamPressure;
        //freestreamValue uniform $pOut;

        type            totalPressure;
        p0                uniform 115775;
        value           uniform 115775;
    
        //type            fixedValue;
        //value           uniform 84636.34;
    }

    OUTLET
    {
        
        //type            zeroGradient;         
        
        //type            freestreamPressure;
        //freestreamValue $internalField;    
            
        type            fixedValue;
        value           $internalField;

    }

    CASCADE
    {
        type            zeroGradient;
    }

    "(TOP|BOTTOM)"
    {
        type            cyclicAMI;
    }

    frontAndBackPlanes
    {
        type            empty;
    }
}


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

U file,

/*--------------------------------*- C++ -*----------------------------------* \
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  v2112                                 |
|   \\  /    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
{
    INLET
    {
        //type            pressureInletOutletVelocity;
        //value           uniform (110.534 135.673 0);

        //type            freestreamVelocity;
        //freestreamValue uniform $Uinlet;
        //value           uniform $Uinlet;
    
        //type            fixedValue;
        //value           uniform (232.43 20.34 0);
        
        type pressureDirectedInletVelocity;
        inletDirection uniform (0.631623456 -0.775275312 0);
        value uniform (0 0 0);

        //type            pressureInletOutletVelocity;
        //value           uniform (0 0 0);
        //inletValue      uniform (0 0 0);
    }

    OUTLET
    {
        //type           inletOutlet;
       //inletValue    uniform (0 0 0);
        //value         $internalField;

        type            pressureInletOutletVelocity;
        value           uniform (0 0 0);
        inletValue      uniform (0 0 0);

        //type            fixedValue;
        //value           uniform (0 0 0);

        //type            zeroGradient;
    }

    CASCADE
    {
        type            noSlip;
    }
    
    "(TOP|BOTTOM)"
    {
        type            cyclicAMI;
    }

    frontAndBackPlanes
    {
        type            empty;
    }

    
}


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

T file,

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  v2112                                 |
|   \\  /    A nd           | Website:  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 340.2;

boundaryField
{
    INLET
    {
        type            totalTemperature;
        gamma           1.4;
        T0              $internalField;

        //type            inletOutlet;
        //inletValue      uniform $Tinlet;
        //value           $inletValue;
        
        //type            fixedValue;
        //value           $internalField;
    }
    
    OUTLET
    {
        type            inletOutlet;
        inletValue      $internalField;
        value           $internalField;
    }

    CASCADE
    {
        type            zeroGradient;
    }

    
    "(TOP|BOTTOM)"
    {
        type            cyclicAMI;
    }

    frontAndBackPlanes
    {
        type            empty;
    }

    
}


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

please help