[Slanth]

Hello, everyone. I want to implement a time-varying total pressure BC. So I use the uniformTotalPressure in OpenFOAM-2.2.2. The velocity boundary is pressureInletOutletVelocity. But as time going on, I always obtain the negative temperature, which is insane.

However, if I just use totalpressure BC without time-varying properties. The simulation is ok. The case aims at solving compressible flow using LES. Piso is used.

Any assistance is appreciated, thanks very much.

[Slanth]

The pressure boundary and velocity boundary are belows

PHP Code:

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  2.2.2                                 |
|   \\  /    A nd           | Web:      www.OpenFOAM.org                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       volScalarField;
    location    "492";
    object      p;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dimensions      [1 -1 -2 0 0 0 0];

internalField   uniform 118847;

boundaryField
{
    intake_intake
    {

        type            uniformTotalPressure;
        U               U;
        phi             phi;
        rho             none;
        psi             psi;
        gamma           1.4;
        pressure        tableFile;
        tableFileCoeffs 
       { 
          fileName     "$FOAM_CASE/constant/p_intake" 
          outOfBounds  clamp; 
       } 

    }
        exhaust_exhaust
    {

        type            uniformTotalPressure;
        U               U;
        phi             phi;
        rho             none;
        psi             psi;
        gamma           1.4;
        pressure        tableFile;
        tableFileCoeffs 
       { 
          fileName     "$FOAM_CASE/constant/p_Exhaust" 
          outOfBounds  clamp; 
       } 


    }
    intake_wall_intake_wall
    {
        type            zeroGradient;
    }
    valve1_seat_valve1_seat
    {
        type            zeroGradient;
    }

    exhaust_wall_exhaust_wall
    {
        type            zeroGradient;
    }
    valve2_seat_valve2_seat
    {
        type            zeroGradient;
    }
    cylinderHead
    {
        type            zeroGradient;
    }
    SparkPlug_SparkPlug
    {
        type            zeroGradient;
    }
    stem_wall1_stem_wall1
    {
        type            zeroGradient;
    }
    stem_wall2_stem_wall2
    {
        type            zeroGradient;
    }
    piston
    {
        type            zeroGradient;
    }
    liner
    {
        type            zeroGradient;
    }
    valve1_stem_valve1_stem
    {
        type            zeroGradient;
    }
    valve1_top_up_valve1_top_up
    {
        type            zeroGradient;
    }
    valve1_top_down_valve1_top_down
    {
        type            zeroGradient;
    }
    valve1_bottom_valve1_bottom
    {
        type            zeroGradient;
    }
    valve2_stem_valve2_stem
    {
        type            zeroGradient;
    }
    valve2_top_up_valve2_top_up
    {
        type            zeroGradient;
    }
    valve2_top_down_valve2_top_down
    {
        type            zeroGradient;
    }
    valve2_bottom_valve2_bottom
    {
        type            zeroGradient;
    }
    valve2Baffle_region0
    {
        type            zeroGradient;
    }
    valve2Baffle_region0_slave
    {
        type            zeroGradient;
    }
}


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


PHP Code:

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  2.2.2                                 |
|   \\  /    A nd           | Web:      www.OpenFOAM.org                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       volVectorField;
    location    "492";
    object      U;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dimensions      [0 1 -1 0 0 0 0];

internalField   uniform (0 0 0);

boundaryField
{
    intake_intake
    {
        type            pressureInletOutletVelocity;
        value           uniform (0 0 0);
    }
    intake_wall_intake_wall
    {
        type            fixedValue;
        value           uniform (0 0 0);
    }
    valve1_seat_valve1_seat
    {
        type            fixedValue;
        value           uniform (0 0 0);
    }
    exhaust_exhaust
    {
        type            pressureInletOutletVelocity;
        value           uniform (0 0 0);
    }
    exhaust_wall_exhaust_wall
    {
        type            fixedValue;
        value           uniform (0 0 0);
    }
    valve2_seat_valve2_seat
    {
        type            fixedValue;
        value           uniform (0 0 0);
    }
    cylinderHead
    {
        type            fixedValue;
        value           uniform (0 0 0);
    }
    SparkPlug_SparkPlug
    {
        type            fixedValue;
        value           uniform (0 0 0);
    }
    stem_wall1_stem_wall1
    {
        type            fixedValue;
        value           uniform (0 0 0);
    }
    stem_wall2_stem_wall2
    {
        type            fixedValue;
        value           uniform (0 0 0);
    }
    piston
    {
        type            movingWallVelocity;
        value           uniform (0 0 0);
    }
    liner
    {
        type            fixedValue;
        value           uniform (0 0 0);
    }
    valve1_stem_valve1_stem
    {
        type            fixedValue;
        value           uniform (0 0 0);
    }
    valve1_top_up_valve1_top_up
    {
        type            movingWallVelocity;
        value           uniform (0 0 0);
    }
    valve1_top_down_valve1_top_down
    {
        type            movingWallVelocity;
        value           uniform (0 0 0);
    }
    valve1_bottom_valve1_bottom
    {
        type            movingWallVelocity;
        value           uniform (0 0 0);
    }
    valve2_stem_valve2_stem
    {
        type            fixedValue;
        value           uniform (0 0 0);
    }
    valve2_top_up_valve2_top_up
    {
        type            fixedValue;
        value           uniform (0 0 0);
    }
    valve2_top_down_valve2_top_down
    {
        type            fixedValue;
        value           uniform (0 0 0);
    }
    valve2_bottom_valve2_bottom
    {
        type            fixedValue;
        value           uniform (0 0 0);
    }
    valve2Baffle_region0
    {
        type            fixedValue;
        value           uniform (0 0 0);
    }
    valve2Baffle_region0_slave
    {
        type            fixedValue;
        value           uniform (0 0 0);
    }
}


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


[Slanth]

I have solved the problem, just because the uniform pressure within the domain is too small, which induces numerical instability.

But now I met another question, calculation inflow has no problems. But when reverse flow happens, negative temperature occurs near the valve-intake BC (which is the only exit).
I have attached the temperature and velocity distribution as below, the left fig is overall view while the right fig is the enlarged view.
[IMG][/IMG] [IMG][/IMG]
Any advice is appreciated....