# uniformTotalPressure BC problems

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 January 4, 2015, 03:54 uniformTotalPressure BC problems #1 New Member   Join Date: Mar 2013 Posts: 10 Rep Power: 4 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.

 January 4, 2015, 04:22 #2 New Member   Join Date: Mar 2013 Posts: 10 Rep Power: 4 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);     } } // ************************************************************************* //  ```

January 12, 2015, 03:04
#3
New Member

Join Date: Mar 2013
Posts: 10
Rep Power: 4
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....
Attached Images
 24_CH5.jpg (24.9 KB, 16 views) 24_CH6.jpg (38.5 KB, 13 views)

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