|April 29, 2014, 22:45||
Erroneous Courant Number in FOAM log?
Join Date: Mar 2009
Posts: 72Rep Power: 9
I'm trying to use the adjustTimeStep option in controDict to run my LES simulation. However, the courant number reported at run time is so high that OpenFOAM was forced to constantly reduce the time step size until it hits ~1e-30 and the whole simulation just crashed. I revised the simulation to run on fixed time step, and was getting the following message in my log:
Courant Number mean: 0.0042170848 max: 136.39391 Time = 75.642 DILUPBiCG: Solving for Ux, Initial residual = 0.00032185865, Final residual = 3.2946399e-08, No Iterations 1 DILUPBiCG: Solving for Uy, Initial residual = 0.00029752553, Final residual = 3.1410567e-08, No Iterations 1 DILUPBiCG: Solving for Uz, Initial residual = 0.00066511108, Final residual = 7.6629127e-08, No Iterations 1 GAMG: Solving for p, Initial residual = 0.0046290147, Final residual = 7.3302722e-05, No Iterations 2 GAMG: Solving for p, Initial residual = 7.3305549e-05, Final residual = 9.6448053e-07, No Iterations 13 time step continuity errors : sum local = 7.9685318e-13, global = 8.7932007e-14, cumulative = 1.3817586e-10 ExecutionTime = 53373.4 s ClockTime = 53430 s
Time = 75 Reading phi Calculating incompressible Co Co max : 0.032720504 End Time = 76 Reading phi Calculating incompressible Co Co max : 0.032659777 End
EDIT: I should add that the simulation was stable for the entire simulation even with maxCo reported at ~135.
EDIT2: I looked into OpenFOAM source code, and the Courant number in Co is calculated using
//- Return 1 if the flux field is volumetric i.e. incompressible flow?, otherwise return rho // from the database tmp<volScalarField> rho(const surfaceScalarField& p) const;
On a side note, I ran the same simulation using a finer mesh (2/3 of original grid size), and obtained significantly lower Courant number of ~0.1 in FOAM log, which enabled me to turn on adjustTimeStep.
Last edited by cwang5; April 30, 2014 at 07:19.
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