| myuse2 |
April 1, 2018 23:46 |
Anisotropic (~2) divergence/Courant number explosion
Dear all,
I'm sure this is an easy thing as I'm new to OpenFOAM. I'm trying to run a simple laminar flow in a 2.5x0.41x0.41 channel with x-inlet velocity = 1 and nu = 1. Everything works fine with an isotropic mesh, but when I increase the anisotropy ratio to 2 or beyond (meshCheck is ok execpt for Max aspect ratio = 2.0098 OK, which should be fine I think) the Courant number steadily increases even though the linear solvers converge fine.
I'm using icoFoam ddtScheme Euler with a small time step 0.005 (and potential flow initialization), and have three boundary patches:
Code:
1: wall - U: type fixedValue; value uniform (0 0 0); p: type zeroGradient;
2(x==0): patch - U: type fixedValue; value uniform (1 0 0); p: type zeroGradient;
3(x==2.5): patch - U: type zeroGradient; p: type fixedValue; value uniform 0;
Solver output looks like this:
Code:
...
Time = 0.02
Courant Number mean: 0.396073 max: 0.595328
DILUPBiCG: Solving for Ux, Initial residual = 0.710458, Final residual = 6.05412e-009, No Iterations 29
DILUPBiCG: Solving for Uy, Initial residual = 0.555298, Final residual = 8.24426e-009, No Iterations 27
DILUPBiCG: Solving for Uz, Initial residual = 0.555298, Final residual = 8.24421e-009, No Iterations 27
GAMG: Solving for p, Initial residual = 0.146766, Final residual = 8.4081e-009, No Iterations 24
GAMG: Solving for p, Initial residual = 3.12959e-010, Final residual = 3.12959e-010, No Iterations 0
GAMG: Solving for p, Initial residual = 3.12959e-010, Final residual = 3.12959e-010, No Iterations 0
time step continuity errors : sum local = 4.908e-010, global = 1.35872e-010, cumulative = 3.72047e-010
GAMG: Solving for p, Initial residual = 0.00478919, Final residual = 9.99079e-009, No Iterations 19
GAMG: Solving for p, Initial residual = 5.2169e-007, Final residual = 7.70071e-009, No Iterations 6
GAMG: Solving for p, Initial residual = 7.70139e-009, Final residual = 7.70139e-009, No Iterations 0
time step continuity errors : sum local = 2.30206e-010, global = -6.38586e-011, cumulative = 3.08189e-010
ExecutionTime = 8.047 s ClockTime = 8 s
Time = 0.025
Courant Number mean: 0.469957 max: 1.39104
DILUPBiCG: Solving for Ux, Initial residual = 0.338095, Final residual = 6.63966e-009, No Iterations 28
DILUPBiCG: Solving for Uy, Initial residual = 0.381617, Final residual = 7.22101e-009, No Iterations 27
DILUPBiCG: Solving for Uz, Initial residual = 0.381617, Final residual = 7.221e-009, No Iterations 27
GAMG: Solving for p, Initial residual = 0.285914, Final residual = 6.1955e-009, No Iterations 25
GAMG: Solving for p, Initial residual = 1.60704e-010, Final residual = 1.60704e-010, No Iterations 0
GAMG: Solving for p, Initial residual = 1.60704e-010, Final residual = 1.60704e-010, No Iterations 0
time step continuity errors : sum local = 2.46742e-010, global = -6.86928e-011, cumulative = 2.39496e-010
GAMG: Solving for p, Initial residual = 0.00646772, Final residual = 5.10226e-009, No Iterations 20
GAMG: Solving for p, Initial residual = 1.52933e-007, Final residual = 9.2095e-009, No Iterations 4
GAMG: Solving for p, Initial residual = 9.20973e-009, Final residual = 9.20973e-009, No Iterations 0
time step continuity errors : sum local = 4.68844e-010, global = 1.30753e-010, cumulative = 3.70249e-010
ExecutionTime = 9.923 s ClockTime = 10 s
Time = 0.03
Courant Number mean: 0.399864 max: 0.877514
DILUPBiCG: Solving for Ux, Initial residual = 0.553235, Final residual = 7.50458e-009, No Iterations 29
DILUPBiCG: Solving for Uy, Initial residual = 0.664806, Final residual = 6.56398e-009, No Iterations 28
DILUPBiCG: Solving for Uz, Initial residual = 0.664806, Final residual = 6.56398e-009, No Iterations 28
GAMG: Solving for p, Initial residual = 0.240677, Final residual = 8.57317e-009, No Iterations 24
GAMG: Solving for p, Initial residual = 3.59447e-010, Final residual = 3.59447e-010, No Iterations 0
GAMG: Solving for p, Initial residual = 3.59447e-010, Final residual = 3.59447e-010, No Iterations 0
time step continuity errors : sum local = 5.52764e-010, global = 1.5542e-010, cumulative = 5.25669e-010
GAMG: Solving for p, Initial residual = 0.00873356, Final residual = 5.62807e-009, No Iterations 20
GAMG: Solving for p, Initial residual = 2.56358e-007, Final residual = 7.65837e-009, No Iterations 5
GAMG: Solving for p, Initial residual = 7.6587e-009, Final residual = 7.6587e-009, No Iterations 0
time step continuity errors : sum local = 2.56423e-010, global = -7.21304e-011, cumulative = 4.53539e-010
ExecutionTime = 11.86 s ClockTime = 12 s
Time = 0.035
Courant Number mean: 0.462337 max: 1.70965
Time = 0.04
Courant Number mean: 0.406624 max: 1.26753
Time = 0.045
Courant Number mean: 0.470408 max: 2.2144
...
I would really apreciate if someone has any idea what could be the issue (the problem files are attached here https://we.tl/kw9XFZmjWi). |
