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-   -   Best Practices for Internal Compressible Flows (https://www.cfd-online.com/Forums/openfoam/77068-best-practices-internal-compressible-flows.html)

 jason.ryon June 11, 2010 11:47

Best Practices for Internal Compressible Flows

1 Attachment(s)
I understand this is a bit of a loaded question, but I would like to know the "best" way to setup a time-accurate, subsonic, compressible, internal flow (example is an air nozzle with an applied inlet and exit pressure).

Currently I use the rhoPisoFoam solver.

I understand why there are so many options, and the flexibility is of OpenFOAM is one of it's best qualities! However, I am wanting to know which settings you would select to give the best blend of accuracy, stability, and efficiency (speed).

Please post what you would use - especially for solvers, schemes and boundary condition types.

Here is a generic case of a "swirling nozzle" in an airbox, where pressure is specified at the inlet, and exit.

Attachment 3740

These are some of the "parameters" I have tried adjusting, but I can't seem to get it to be stable when using 2nd order schemes (runs for quite a long time then diverges)

1.) Boundary Conditions to use at inlet
U: pressureInletVelocity / zeroGradient / other
p: totalPressure / other

2.) Boundary Conditions to use at outlet
U: zeroGradient / fluxCorrectedVelocity / pressureInletOutletVelocity / other
p: fixedValue / other

3.) Schemes:
Second Order: Gauss limitedLinear 1 / Gauss linear / other
First Order: Gauss upwind / other

4.) Solvers:
p: GAMG / PCG / ICCG / other
everything else: PBiCG/DILU / other

5.) Solver tolerance
tolerances: 1e-10 / 1e-5
relTol: 0 / .001

5.) PISO
nCorrectors 4
nNonOrthogonalCorrectors 2
momentumPredictor yes

6.) Relaxation Factors:
0.7 on everything except p=0.3 and rho = 0.05

7.) Fixed Time Step vs. Adjustable Time Step (with max CFL = 1.0)

8.) Thermophysical properties:
thermoType hPsiThermo<pureMixture<sutherlandTransport<specieT hermo<hConstThermo<perfectGas>>>>>;
mixture air 1 28.9 1007 0 1.4792e-6 116;