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Friendly December 14, 2019 10:18

RhoCentralFoam sudden increase of u and drop of T
 
Hi,


I am trying to simulate a supersonic outflow from a pipe into the free environment.

The inlet patch is the beginning of the pipe.
The pipe is convergent and the smallest cross section is the exit.
The outlet is a wide box which resembles the free environment.


The problem arises soon after I start the simulation. Right after the inlet the velocity increases heavily from 0 to 1000 m/s, the temperature drops to almost 0 K,
then even further to negative values which leads to the stop of the simulation.


I think the problem are my BCs. The mesh is easy to generate and has a good quality. The Co-number is 0.2. I am using rhoCentralFoam and openFOAM 4.1.




My boundary conditions are:


for p:


Code:

internalField  uniform 1e5;



    inlet
    {
    type            totalPressure;
    gamma          1.4;
    p0              uniform 100e5;
    }



  outlet
    {
        type            waveTransmissive;
        field          p;
        psi            thermo:psi;
        gamma          1.4;
        fieldInf        1e5;
        lInf            1;
        value          uniform 1e5;
    }




    wall
    {
        type            zeroGradient;
    }

for u


Code:



internalField  uniform (0 0 0);


inlet
    {
    type            fixedValue;
    value        uniform (0 0 0);
    }

    outlet
    {
        type            inletOutlet;
        inletValue      uniform (0 0 0);
        value        uniform (0 0 0);


    wall
    {
        type            fixedValue;
      inletValue      uniform (0 0 0);
    }

for T


Code:



internalField  uniform 293.15;


inlet
    {
    type    fixedValue;
    value    uniform 293.15;

    }

    outlet
    {
        type            zeroGradient;
    }
    wall
    {
        type            zeroGradient;
    }


emjay December 14, 2019 19:11

Hello Friendly,

does your inlet condition for the U variable make sense?

Because you specify a totalpressure condition and for u:
inlet
{
type fixedValue;
value uniform (0 0 0);
}

this b.c. is like a solid wall. Could you test your U.inlet with zeroGradient?

Friendly December 15, 2019 07:21

Oh yes sry, I copied i from the wrong folder it seems.


Here is my real u inlet:


inlet
{

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


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