# Best Practices for Internal Compressible Flows

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 June 11, 2010, 11:47 Best Practices for Internal Compressible Flows #1 New Member   Jason Ryon Join Date: Oct 2009 Posts: 17 Rep Power: 7 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. swirler.png 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>>>>; mixture air 1 28.9 1007 0 1.4792e-6 116; Thanks for your help! Jason

 Tags internal, rhopisofoam, swirler

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