[shang2]

I have been trying to run this Mach 2.5 supersonic nozzle through OpenFoam and can't seem to figure out the correct boundary conditions. For reference, this is a nozzle that is attached to the 15cm x 15cm supersonic wind tunnel at NASA GRC.

Boundary conditions are:

• Temp = 520 R
• Inlet: Total Pressure = 34.6 PSI
• Outlet: Static Pressure = 1.78 PSI

After trying out a large number of combinations of boundary conditions (read as 50+), this following one seems to work the best:

Pressure, p

{
internalField   uniform 238559;

boundaryField
    inlet
    {
        type            totalPressure;
        gamma           1.4;
        p0              uniform 238559;
        value           $internalField;
    }
    outlet
    {
        type            waveTransmissive;
        gamma           1.4;
        fieldInf        12272.7;
        lInf            0.005;
        value           uniform 12272.7;
    }
    nozzle
    {
        type            zeroGradient;
    }
}

Temperature, T

{
    inlet
    {
        type            fixedValue;
        value           uniform 348.432;
    }
    outlet
    {
        type            zeroGradient;
    }
    nozzle
    {
        type            zeroGradient;
    }
}

Velocity, U
(changing the wall condition from slip to noSlip seems to not make a big difference with the centerline velocity)

{
    inlet
    {
        type            zeroGradient;
    }
    outlet
    {
        type            zeroGradient;
    }
    nozzle
    {
        type            noSlip;
    }
}

I get an outlet centerline velocity of around 630m/s or about Mach 1.83, which is definitely not correct. Do any of you guys have any suggestions as to what is wrong and why I am not getting Mach 2.5? Also, why do I have to use waveTransmissive instead of fixedValue for the outlet pressure? If I use fixedValue, I get a huge velocity discontinuity at the outlet.

My case file exceeds the attachment limit, so I have, instead, put them in my Google Drive, accessible here: https://drive.google.com/open?id=1YQ...T9sU9mh8mpQw8h

Thanks in advance for the help. I have been staring at this for the past 2 weeks, making little progress if any, albeit learning a lot about OpenFoam.

[lukasf]

Hi Shang,


why did you choose the value of lInf? What does it represent for you?


What Solver are you using? I must be a compressible one. The waveTransmissive boundary condition is important to let pressure waves exit your CFD domain. Otherwise they get reflected and influence your solution.


What is your progress?



Lukas