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New_Old November 28, 2016 14:59
Reported phi values exactly twice as high as expected
 
2 Attachment(s)
Hello everyone,

I am new to OpenFoam and today I was getting familiar with the run-time monitoring possibilities when I spotted some strange results.

I have spent quite some time trying to figure this out with no luck, but I believe I have now narrowed the problem down to the point where a more experienced user could easily tell me what's going on.

I attach here two small cases, ready to go on v1606+ (./Allrun).Those are somewhat modified versions of the multiRegionHeater tutorial case:
- case 1 is a transient run, very similar to the original tutorial provided with my version of OpenFOAM (v1606+ on Windows).
- case 2 is a steady-state analysis of the the same problem.

For both case I monitor what is going on at minX on the water side (inlet, fixed velocity), and obtain the following results:

Case 1:
Code:
- Total area:        4.00000000e-03
- average(U):        (1.00000000e-03 0.00000000e+00 0.00000000e+00)
- sum(phi):        -4.00000000e-03
Case 2:
Code:
- Total area:        4.0000000e-03
- average(U):        (1.0000000e-03 0.0000000e+00 0.0000000e+00)
- sum(phi):        -8.0000000e-06
The reported areas and velocities are correct. So is Phi for case one, assuming OpenFOAM reports a mass flow rate in this case.
However, I can't understand how Phi is computed in case two. A volumetric flow rate would explain the different order of magnitude but the reported flow rate would still be twice as high as I would expect.

I have tried to run case 2 on a single processor, which didn't change the results.

I would be extremely thankful if someone could have a look at this.

Cheers
/Jay

New_Old December 2, 2016 06:44
Update
 
I believe I have identified what the problem was:
As a consequence of some shameless copy-pasting of the fvSolution files from a steady-state tutorial, and although I had defined the fluid density as constant (1000 kg/m3), those SIMPLE settings were limiting the density to 2 kg/m3.

Lesson learned... :o

Code:
SIMPLE
{
    momentumPredictor on;
    nNonOrthogonalCorrectors 0;
    pRefCell        0;
    pRefValue      100000;
    rhoMin          0.2;
    rhoMax          2;
}


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