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-   -   rhoPisoFoam stability problems at low Mach (https://www.cfd-online.com/Forums/openfoam/80541-rhopisofoam-stability-problems-low-mach.html)

 ivan_cozza September 29, 2010 05:13

rhoPisoFoam stability problems at low Mach

Hi Foamers,
I have some stability problems using rhoPisoFoam in a very low Mach number circular cylinder case (M < 0.1 ).

It seems that everything coes ok, but after a certain time the k blows up in one iteration:

Time = 2.07181

diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0
DILUPBiCG: Solving for Ux, Initial residual = 3.3515918e-06, Final residual = 2.6552446e-11, No Iterations 4
DILUPBiCG: Solving for Uy, Initial residual = 0.00034732351, Final residual = 7.7333382e-11, No Iterations 6
DILUPBiCG: Solving for h, Initial residual = 1.9780692e-05, Final residual = 3.2882524e-11, No Iterations 5
GAMG: Solving for p, Initial residual = 1.4662108e-05, Final residual = 3.4098026e-11, No Iterations 3
GAMG: Solving for p, Initial residual = 1.4355534e-09, Final residual = 1.348025e-11, No Iterations 1
diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0
time step continuity errors : sum local = 6.9308425e-15, global = 5.62283e-16, cumulative = -6.8253592e-11
DILUPBiCG: Solving for h, Initial residual = 4.4513919e-07, Final residual = 7.2640766e-11, No Iterations 2
GAMG: Solving for p, Initial residual = 8.8319331e-08, Final residual = 9.1747833e-11, No Iterations 1
GAMG: Solving for p, Initial residual = 1.6134773e-10, Final residual = 1.5766157e-11, No Iterations 1
diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0
time step continuity errors : sum local = 8.0791787e-15, global = 7.3381385e-16, cumulative = -6.8252858e-11
DILUPBiCG: Solving for h, Initial residual = 1.1455624e-07, Final residual = 3.3177739e-11, No Iterations 2
GAMG: Solving for p, Initial residual = 2.33519e-08, Final residual = 3.9311579e-11, No Iterations 1
GAMG: Solving for p, Initial residual = 5.7477619e-11, Final residual = 5.7477619e-11, No Iterations 0
diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0
time step continuity errors : sum local = 2.8983277e-14, global = 9.4854643e-16, cumulative = -6.825191e-11
DILUPBiCG: Solving for omega, Initial residual = 1.1586969e-09, Final residual = 1.5913977e-11, No Iterations 1
DILUPBiCG: Solving for k, Initial residual = 6.7968037e-06, Final residual = 1.1665505e-11, No Iterations 4
ExecutionTime = 32270.25 s ClockTime = 32976 s

Courant Number mean: 0.01038351 max: 0.49977902
deltaT = 1.2007647e-05
Calculating averages

Time = 2.07183

diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0
DILUPBiCG: Solving for Ux, Initial residual = 3.3519044e-06, Final residual = 2.6542498e-11, No Iterations 4
DILUPBiCG: Solving for Uy, Initial residual = 0.00034837914, Final residual = 7.7420122e-11, No Iterations 6
DILUPBiCG: Solving for h, Initial residual = 1.974787e-05, Final residual = 3.2719475e-11, No Iterations 5
GAMG: Solving for p, Initial residual = 1.4652224e-05, Final residual = 3.3568677e-11, No Iterations 3
GAMG: Solving for p, Initial residual = 1.4369205e-09, Final residual = 1.3084825e-11, No Iterations 1
diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0
time step continuity errors : sum local = 6.7074558e-15, global = 2.4984506e-16, cumulative = -6.825166e-11
DILUPBiCG: Solving for h, Initial residual = 4.346773e-07, Final residual = 8.1745667e-11, No Iterations 2
GAMG: Solving for p, Initial residual = 8.6121702e-08, Final residual = 8.9788315e-11, No Iterations 1
GAMG: Solving for p, Initial residual = 1.5921841e-10, Final residual = 1.5979726e-11, No Iterations 1
diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0
time step continuity errors : sum local = 8.1557798e-15, global = 3.082739e-16, cumulative = -6.8251351e-11
DILUPBiCG: Solving for h, Initial residual = 1.1225582e-07, Final residual = 2.7701056e-11, No Iterations 2
GAMG: Solving for p, Initial residual = 2.2885971e-08, Final residual = 3.9740809e-11, No Iterations 1
GAMG: Solving for p, Initial residual = 5.7951838e-11, Final residual = 5.7951838e-11, No Iterations 0
diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0
time step continuity errors : sum local = 2.9189666e-14, global = 5.7728127e-16, cumulative = -6.8250774e-11
DILUPBiCG: Solving for omega, Initial residual = 1.1586426e-09, Final residual = 1.6053013e-11, No Iterations 1
DILUPBiCG: Solving for k, Initial residual = 6.7971795e-06, Final residual = 4.5984526e+109, No Iterations 1001
bounding k, min: -3.4221657e+117 max: 3.0685409e+117 average: -2.3638443e+112
ExecutionTime = 32271.31 s ClockTime = 32977 s

After that, the run blows up. It's strange because before this error, the results are very good.

I'm using backward time schemes, and boundedBackward 0.9 for k and Omega, and linearUpwind schemes for div.

Any suggestions?

Thanks!

 ivan_cozza October 1, 2010 11:03

No ideas?
The stuff get stranger, it seems that the calculation blows up, no matter on what kind of time scheme I use (I tryed backward, boundedBackward 0.8 for k and omega, CrankNicholson 1)...

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