[ncl94]

Hello everyone,

this is a newbie's question, but I took the pitzDaily (LES/pisoFoam) example to try the adjustable time step, however it looks like it the time step is not being calculated to satisfy the maxCo I defined. I attached my controlDict here. I was going through the code and I saw that writeInterval can interfere with the code updating the time step, so I tried different values (1e3 to 1e-10) and nothing seems to change the results.

PS: everything else is from the pitzDaily case, I just changed the controlDict.

[Sebastiaan]

I don't see anything obviously wrong, could you perhaps provide a piece of your log file? Do you really want to write results with each 10^-10 seconds? And do you expect the required time step for co<1 to be lower than that?

[ncl94]

Originally Posted by Sebastiaan

Do you really want to write results with each 10^-10 seconds?

Not really, that is just something I was trying to see the effects of writeInterval when having an adjustable time step

Originally Posted by Sebastiaan

And do you expect the required time step for co<1 to be lower than that?

Lower than the writeInterval? No.
Lower than the deltaT I specified in controlDict?Yes.






Sorry for not attaching the log file instead of just writing it here, but I am getting a weird message whenever I try to attach any kind of file. Anyway, there it is:


--------------------------------------------------------------------------------------------------------------------

Time = 2e-05

Courant Number mean: 0.000174979 max: 0.0631777
smoothSolver: Solving for Ux, Initial residual = 1, Final residual = 2.48998e-07, No Iterations 2
smoothSolver: Solving for Uy, Initial residual = 1, Final residual = 2.6611e-07, No Iterations 2
GAMG: Solving for p, Initial residual = 1, Final residual = 0.0982953, No Iterations 20
time step continuity errors : sum local = 3.44036e-05, global = -1.90151e-06, cumulative = -1.90151e-06
GAMG: Solving for p, Initial residual = 0.0123119, Final residual = 6.67732e-07, No Iterations 8
time step continuity errors : sum local = 2.62174e-08, global = -2.66804e-09, cumulative = -1.90418e-06
smoothSolver: Solving for k, Initial residual = 0.72442, Final residual = 1.51991e-07, No Iterations 3
bounding k, min: 0 max: 0.000841637 average: 1.64512e-07
ExecutionTime = 0.18 s ClockTime = 0 s

fieldAverage fieldAverage1:
Reading/initialising field UMean
Reading/initialising field pMean
Reading/initialising field UPrime2Mean
Reading/initialising field pPrime2Mean

fieldAverage fieldAverage1 write:
Calculating averages

Writing average fields

scalarTransport execute: s
smoothSolver: Solving for s, Initial residual = 1, Final residual = 8.10247e-06, No Iterations 2

scalarTransport write: scalarTransport
s

Time = 4e-05

Courant Number mean: 0.0848829 max: 1.89314
smoothSolver: Solving for Ux, Initial residual = 0.858153, Final residual = 4.38444e-06, No Iterations 4
smoothSolver: Solving for Uy, Initial residual = 0.220983, Final residual = 8.45497e-06, No Iterations 4
GAMG: Solving for p, Initial residual = 0.0194081, Final residual = 0.00176716, No Iterations 19
time step continuity errors : sum local = 4.63307e-05, global = -3.7076e-06, cumulative = -5.61177e-06
GAMG: Solving for p, Initial residual = 0.0408878, Final residual = 5.63238e-07, No Iterations 12
time step continuity errors : sum local = 7.69652e-09, global = -1.03697e-09, cumulative = -5.61281e-06
smoothSolver: Solving for k, Initial residual = 0.239396, Final residual = 1.8275e-06, No Iterations 2
bounding k, min: -3.38517e-10 max: 0.00153181 average: 3.74304e-07
ExecutionTime = 0.24 s ClockTime = 0 s

fieldAverage fieldAverage1 write:
Calculating averages

Writing average fields

scalarTransport execute: s
smoothSolver: Solving for s, Initial residual = 0.210501, Final residual = 3.31326e-06, No Iterations 2

scalarTransport write: scalarTransport
s

Time = 6e-05

Courant Number mean: 0.0848805 max: 1.84028
smoothSolver: Solving for Ux, Initial residual = 0.685705, Final residual = 3.32903e-06, No Iterations 4
smoothSolver: Solving for Uy, Initial residual = 0.0878103, Final residual = 4.38787e-06, No Iterations 4
GAMG: Solving for p, Initial residual = 0.017978, Final residual = 0.00174891, No Iterations 17
time step continuity errors : sum local = 2.27482e-05, global = 2.11883e-06, cumulative = -3.49398e-06
GAMG: Solving for p, Initial residual = 0.583057, Final residual = 5.26689e-07, No Iterations 16
time step continuity errors : sum local = 1.70612e-10, global = 2.06454e-11, cumulative = -3.49396e-06
smoothSolver: Solving for k, Initial residual = 0.146676, Final residual = 6.81688e-06, No Iterations 4
bounding k, min: -1.50636e-07 max: 0.00217707 average: 6.33037e-07
ExecutionTime = 0.3 s ClockTime = 0 s

fieldAverage fieldAverage1 write:
Calculating averages

Writing average fields

scalarTransport execute: s
smoothSolver: Solving for s, Initial residual = 0.117555, Final residual = 3.4525e-06, No Iterations 2

scalarTransport write: scalarTransport
s

Time = 8e-05

Courant Number mean: 0.0847656 max: 1.76053
smoothSolver: Solving for Ux, Initial residual = 0.00879533, Final residual = 3.64488e-06, No Iterations 3
smoothSolver: Solving for Uy, Initial residual = 0.0023919, Final residual = 4.50489e-06, No Iterations 3
GAMG: Solving for p, Initial residual = 0.176207, Final residual = 0.0133852, No Iterations 2
time step continuity errors : sum local = 3.1426e-06, global = 7.29022e-08, cumulative = -3.42106e-06
GAMG: Solving for p, Initial residual = 0.0224733, Final residual = 3.64068e-07, No Iterations 11
time step continuity errors : sum local = 8.04213e-11, global = -1.0749e-11, cumulative = -3.42107e-06
smoothSolver: Solving for k, Initial residual = 0.105586, Final residual = 1.8306e-06, No Iterations 6
bounding k, min: -3.3322e-07 max: 0.0027276 average: 1.0776e-06
ExecutionTime = 0.35 s ClockTime = 0 s

fieldAverage fieldAverage1 write:
Calculating averages

Writing average fields

scalarTransport execute: s
smoothSolver: Solving for s, Initial residual = 0.0814703, Final residual = 4.10346e-06, No Iterations 2

scalarTransport write: scalarTransport
s

Time = 0.0001

Courant Number mean: 0.0845884 max: 1.69682
smoothSolver: Solving for Ux, Initial residual = 0.00879353, Final residual = 2.88955e-06, No Iterations 3
smoothSolver: Solving for Uy, Initial residual = 0.00173623, Final residual = 3.72738e-06, No Iterations 3
GAMG: Solving for p, Initial residual = 0.109361, Final residual = 0.0054413, No Iterations 3
time step continuity errors : sum local = 1.09907e-06, global = -1.89206e-07, cumulative = -3.61027e-06
GAMG: Solving for p, Initial residual = 0.010983, Final residual = 6.11753e-07, No Iterations 11
time step continuity errors : sum local = 1.07575e-10, global = 7.201e-12, cumulative = -3.61027e-06
smoothSolver: Solving for k, Initial residual = 0.0849395, Final residual = 1.70522e-06, No Iterations 6
bounding k, min: -1.55854e-08 max: 0.00357542 average: 1.99527e-06
ExecutionTime = 0.4 s ClockTime = 0 s

fieldAverage fieldAverage1 write:
Calculating averages

Writing average fields

scalarTransport execute: s
smoothSolver: Solving for s, Initial residual = 0.062312, Final residual = 5.05917e-06, No Iterations 2

scalarTransport write: scalarTransport
s

Time = 0.00012

Courant Number mean: 0.0844443 max: 1.64538
smoothSolver: Solving for Ux, Initial residual = 0.00625174, Final residual = 2.99884e-06, No Iterations 3
smoothSolver: Solving for Uy, Initial residual = 0.00145455, Final residual = 3.65718e-06, No Iterations 3
GAMG: Solving for p, Initial residual = 0.109404, Final residual = 0.00763556, No Iterations 8
time step continuity errors : sum local = 1.25652e-06, global = -1.08833e-07, cumulative = -3.7191e-06
GAMG: Solving for p, Initial residual = 0.0157532, Final residual = 4.27e-07, No Iterations 12
time step continuity errors : sum local = 8.47843e-11, global = -1.50146e-11, cumulative = -3.71911e-06
smoothSolver: Solving for k, Initial residual = 0.0603562, Final residual = 8.98367e-06, No Iterations 5
bounding k, min: -7.64728e-06 max: 0.00549997 average: 3.30318e-06
ExecutionTime = 0.46 s ClockTime = 0 s

[Sebastiaan]

My mistake, I forgot that pisoFoam does not support an adjustable time step. You could try pimpleFoam as an alternative. Or if you feel comfortable you could adapt and recompile pisoFoam (see Using adjustableTimeStep in pisoFoam), however I would suggest using pimpleFoam regardless if you intend to operate near the CFL~1 condition as you might need outer iterations for stability (depends highly on the application).

[Sebastiaan]

You migth be interested in this reply by Tobi on configuring pimpleFoam with respect to pisoFoam.

[ncl94]

Thank you very much, Sebastiaan! I didn't know either that some solvers do not offer time step adjustment, I thought it was inherited by every solver.