# Simulation stops with high courant number

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 January 25, 2020, 14:43 Simulation stops with high courant number #1 New Member   Victor Join Date: Mar 2019 Posts: 5 Rep Power: 6 Hi I'm trying to learn OpenFOAM again after being away for a while. I've modified the icoFoam/elbow example with my own mesh. But It stops after a short while. The geometry is just a simple rectangle for testing. control dict: Code: ```application icoFoam; startFrom latestTime; startTime 0; stopAt endTime; endTime 6; deltaT 0.005; writeControl timeStep; writeInterval 20; purgeWrite 0; writeFormat ascii; writePrecision 6; writeCompression off; timeFormat general; timePrecision 6; runTimeModifiable true;``` 0/U: Code: ```dimensions [0 1 -1 0 0 0 0]; internalField uniform (0 0 0); boundaryField { wall { type noSlip; } inlet { type fixedValue; value uniform (0.01 0 0); } outlet { type zeroGradient; } }``` Showing the end: Code: ```Courant Number mean: 0.79581 max: 63.1 smoothSolver: Solving for Ux, Initial residual = 0.685782, Final residual = 9.41785e-06, No Iterations 66 smoothSolver: Solving for Uy, Initial residual = 0.716174, Final residual = 8.69162e-06, No Iterations 63 smoothSolver: Solving for Uz, Initial residual = 0.693323, Final residual = 8.51979e-06, No Iterations 59 DICPCG: Solving for p, Initial residual = 0.713553, Final residual = 0.0356645, No Iterations 156 DICPCG: Solving for p, Initial residual = 0.338417, Final residual = 0.0123583, No Iterations 3 DICPCG: Solving for p, Initial residual = 0.033877, Final residual = 0.00167932, No Iterations 170 time step continuity errors : sum local = 0.00694275, global = 0.000103744, cumulative = -9.99947e-05 DICPCG: Solving for p, Initial residual = 0.129921, Final residual = 0.00645082, No Iterations 151 DICPCG: Solving for p, Initial residual = 0.25175, Final residual = 0.00949852, No Iterations 3 DICPCG: Solving for p, Initial residual = 0.0337265, Final residual = 9.34626e-07, No Iterations 211 time step continuity errors : sum local = 3.23715e-06, global = 1.79642e-08, cumulative = -9.99768e-05 ExecutionTime = 24.94 s ClockTime = 26 s Time = 0.315 Courant Number mean: 1.13275 max: 119.556 smoothSolver: Solving for Ux, Initial residual = 0.684699, Final residual = 9.86724e-06, No Iterations 104 smoothSolver: Solving for Uy, Initial residual = 0.703938, Final residual = 9.742e-06, No Iterations 107 smoothSolver: Solving for Uz, Initial residual = 0.690446, Final residual = 9.77228e-06, No Iterations 131 DICPCG: Solving for p, Initial residual = 0.674098, Final residual = 0.0325922, No Iterations 151 DICPCG: Solving for p, Initial residual = 0.357341, Final residual = 0.0124241, No Iterations 3 DICPCG: Solving for p, Initial residual = 0.0348905, Final residual = 0.00174187, No Iterations 170 time step continuity errors : sum local = 0.00968451, global = 2.81742e-05, cumulative = -7.18026e-05 DICPCG: Solving for p, Initial residual = 0.12856, Final residual = 0.00636255, No Iterations 147 DICPCG: Solving for p, Initial residual = 0.266371, Final residual = 0.00985169, No Iterations 3 DICPCG: Solving for p, Initial residual = 0.0348542, Final residual = 9.78138e-07, No Iterations 211 time step continuity errors : sum local = 4.60704e-06, global = 1.03763e-08, cumulative = -7.17922e-05 ExecutionTime = 25.42 s ClockTime = 26 s Time = 0.32 Courant Number mean: 1.16594 max: 69.504```

 January 28, 2020, 17:35 #2 Senior Member   Svetlana Tkachenko Join Date: Oct 2013 Location: Australia, Sydney Posts: 407 Rep Power: 13 I would suggest to upload the entire case so that others can see your geometry and mesh.

 January 29, 2020, 11:49 #3 Senior Member   Peter Hess Join Date: Apr 2011 Location: Austria Posts: 247 Rep Power: 16 deltaT seams to be very high! Either reduce deltaT to about 0.00005. Or add those two lines to controlDict: maxCo 1; adjustTimeStep yes; Or (better): do both at the same time! Like that the solver will start with a low Co. and modefi deltaT as it need to keep Co under 1! What checkMesh tells? Is your mesh ok? Regards Peter Last edited by peterhess; January 29, 2020 at 13:24.

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