CFD Online Discussion Forums

CFD Online Discussion Forums (https://www.cfd-online.com/Forums/)
-   OpenFOAM (https://www.cfd-online.com/Forums/openfoam/)
-   -   Inlet & outlet both pressure boundary condition (https://www.cfd-online.com/Forums/openfoam/226760-inlet-outlet-both-pressure-boundary-condition.html)

shouvik ghorui May 7, 2020 05:47

Inlet & outlet both pressure boundary condition
 
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 May 12, 2020 15:04

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 May 12, 2020 20:02

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 May 17, 2020 12:27

Quote:

Originally Posted by Tobi (Post 770159)
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 May 17, 2020 12:28

Quote:

Originally Posted by HPE (Post 770123)
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 November 1, 2022 05:39

Please Help
 
1 Attachment(s)
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,

Code:

/*--------------------------------*- 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,


Code:

/*--------------------------------*- 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,


Code:

/*--------------------------------*- 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


All times are GMT -4. The time now is 14:04.