# pimpleFoam screwed up with residual and courant number

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 May 1, 2019, 13:29 pimpleFoam screwed up with residual and courant number #1 Member   Joe lee Join Date: Nov 2018 Posts: 59 Rep Power: 7 I was trying to use pimpleFoam to obtain the transient solution of my simulation. In fvSolution, I followed: https://openfoamwiki.net/index.php/O...hm_in_OpenFOAM to setup. And when I had my first timestep, the residuals went crazy. Here is the residuals plot just after the first timestep(50 iterations): The velocity residuals blew up. Also, in log.pimpleFoam, I found 1. forceCoeffs blew up; 2. courant blew up; 3. PIMPLE: Not converged within 50 iterations 4. last iteration take 1000 iterations for velocity Here is part of the log: Code: ```... PIMPLE: Iteration 49 smoothSolver: Solving for Ux, Initial residual = 0.2628474, Final residual = 0.006348619, No Iterations 1 smoothSolver: Solving for Uy, Initial residual = 0.3153633, Final residual = 0.009944488, No Iterations 1 smoothSolver: Solving for Uz, Initial residual = 0.2931374, Final residual = 0.009416199, No Iterations 1 GAMG: Solving for p, Initial residual = 1.737072e-05, Final residual = 9.476295e-08, No Iterations 4 time step continuity errors : sum local = 0.0003989904, global = 4.242985e-07, cumulative = 5.625885e-07 PIMPLE: Iteration 50 smoothSolver: Solving for Ux, Initial residual = 0.6357956, Final residual = 0.0001464525, No Iterations 1000 smoothSolver: Solving for Uy, Initial residual = 0.7345522, Final residual = 8.67146e-05, No Iterations 1000 smoothSolver: Solving for Uz, Initial residual = 0.7207067, Final residual = 7.978962e-05, No Iterations 1000 GAMG: Solving for p, Initial residual = 0.1127675, Final residual = 8.968816e-08, No Iterations 55 time step continuity errors : sum local = 0.004213623, global = -0.001068937, cumulative = -0.001068374 smoothSolver: Solving for epsilon, Initial residual = 1, Final residual = 0.1651915, No Iterations 1000 smoothSolver: Solving for k, Initial residual = 1, Final residual = 9.930172e-07, No Iterations 81 PIMPLE: Not converged within 50 iterations ExecutionTime = 3608.8 s ClockTime = 3653 s forceCoeffs forceCoeffs1 write: Cm = -1.194991e+17 Cd = -1.60657e+17 Cl = 1.946065e+17 Cl(f) = -2.219587e+16 Cl(r) = 2.168024e+17 Courant Number mean: 242261.2 max: 6.091332e+10 deltaT = 2.897077e-13 Time = 0.00588235``` my questions are: 1. Why would my courant number go so large? I should have limited it in controlDict: Code: ```maxCo 3; maxDaltaT 1;``` 2. Is 50 nOuterCorrector too few for this case? 3. Is any of my setup got wrong?(I will post it at the end) Thank you very much!! fvSolution: Code: ```solvers { p { solver GAMG; smoother DICGaussSeidel; tolerance 1e-7; relTol 0.01; } pFinal { \$p; relTol 0; } "(U|k|epsilon)" { solver smoothSolver; smoother symGaussSeidel; tolerance 1e-06; relTol 0.1; } "(U|k|epsilon)Final" { \$U; tolerance 1e-06; relTol 0; } } PIMPLE { nOuterCorrectors 50; nCorrectors 1; nNonOrthogonalCorrectors 0; outerCorrectorResidualControl { U { tolerance 1e-5; relTol 0; } p { tolerance 5e-4; relTol 0; } } } relaxationFactors { fields { p 0.3; pFinal 1; } equations { "U|k|epsilon" 0.3; "(U|k|epsilon)Final" 1; } }``` controlDict: Code: ```application pimpleFoam; startFrom latestTime; startTime 0; stopAt endTime; endTime 400; deltaT 0.005; writeControl adjustableRunTime; writeInterval 0.1; purgeWrite 0; writeFormat binary; writePrecision 7; writeCompression off; timeFormat general; timePrecision 6; runTimeModifiable yes; adjustTimeStep yes; maxCo 3; maxDaltaT 1; functions { #include "streamLines" #include "cuttingPlane" #include "forceCoeffs" }```

 Tags controldict, convergence, fvsolution, pimplefoam, residuals