[Solo Sails]

Hi,

I am very new to OpenFoam and CFD in general and my knowledge is pretty limited, but could do with some help!

I have been running some fairly hefty cases with good results using SimpleFoam RAS K epsilon, and would like to run the same case using PisoFoam but there is something wrong.

I run the case and it starts, runs about 6 iterations then stops...

Create time

Create mesh for time = 0

Reading field p

Reading field U

Reading/calculating face flux field phi

Selecting incompressible transport model Newtonian
Selecting turbulence model type RASModel
Selecting RAS turbulence model kEpsilon

Starting time loop

Time = 1

Courant Number mean: 0 max: 22.3405
DILUPBiCG: Solving for Ux, Initial residual = 1, Final residual = 0.0177764, No
Iterations 2
DILUPBiCG: Solving for Uy, Initial residual = 1, Final residual = 0.080159, No
Iterations 2
DILUPBiCG: Solving for Uz, Initial residual = 1, Final residual = 0.064155, No
Iterations 2
DICPCG: Solving for p, Initial residual = 1, Final residual = 0.00988745, No It
erations 16
time step continuity errors : sum local = 0.0238766, global = -7.05036e-006, cum
ulative = -7.05036e-006
DICPCG: Solving for p, Initial residual = 0.0429108, Final residual = 8.08946e-
007, No Iterations 32
time step continuity errors : sum local = 1.92361e-005, global = -1.04776e-006,
cumulative = -8.09813e-006
DILUPBiCG: Solving for epsilon, Initial residual = 0.0747366, Final residual =
0.00498244, No Iterations 7
bounding epsilon, min: -0.0552828 max: 3.18431 average: 1.50393
DILUPBiCG: Solving for k, Initial residual = 1, Final residual = 0.0662276, No
Iterations 4
ExecutionTime = 7.753 s ClockTime = 7 s

Time = 2

Courant Number mean: 2.28129 max: 22.3405
DILUPBiCG: Solving for Ux, Initial residual = 0.683011, Final residual = 0.0254
887, No Iterations 4
DILUPBiCG: Solving for Uy, Initial residual = 0.666654, Final residual = 0.0397
083, No Iterations 2
DILUPBiCG: Solving for Uz, Initial residual = 0.541532, Final residual = 0.0400
149, No Iterations 4
DICPCG: Solving for p, Initial residual = 0.310939, Final residual = 0.00303243
, No Iterations 41
time step continuity errors : sum local = 0.0193994, global = -0.00070995, cumul
ative = -0.000718048
DICPCG: Solving for p, Initial residual = 0.168895, Final residual = 8.11337e-0
07, No Iterations 82
time step continuity errors : sum local = 7.50547e-006, global = -1.25482e-007,
cumulative = -0.000718174
DILUPBiCG: Solving for epsilon, Initial residual = 0.133022, Final residual = 0
.00903727, No Iterations 7
bounding epsilon, min: -4.12792 max: 24.4349 average: 1.36762
DILUPBiCG: Solving for k, Initial residual = 0.79566, Final residual = 0.060510
1, No Iterations 14
bounding k, min: -181.446 max: 752.263 average: 0.187323
ExecutionTime = 12.972 s ClockTime = 13 s

Time = 3

Courant Number mean: 9.33323 max: 783.484
DILUPBiCG: Solving for Ux, Initial residual = 0.872314, Final residual = 0.0140
605, No Iterations 2
DILUPBiCG: Solving for Uy, Initial residual = 0.822447, Final residual = 0.0221
085, No Iterations 2
DILUPBiCG: Solving for Uz, Initial residual = 0.908123, Final residual = 0.0650
906, No Iterations 1
DICPCG: Solving for p, Initial residual = 0.655174, Final residual = 0.00654775
, No Iterations 74
time step continuity errors : sum local = 0.0175415, global = -0.000610279, cumu
lative = -0.00132845
DICPCG: Solving for p, Initial residual = 0.661673, Final residual = 5.42804e-0
07, No Iterations 170
time step continuity errors : sum local = 5.70389e-006, global = -1.50213e-007,
cumulative = -0.0013286
DILUPBiCG: Solving for epsilon, Initial residual = 0.977602, Final residual = 0
.0376696, No Iterations 2
bounding epsilon, min: -2.18559e+007 max: 8.2803e+006 average: 6981.89
DILUPBiCG: Solving for k, Initial residual = 1.27945e-007, Final residual = 1.2
7945e-007, No Iterations 0
ExecutionTime = 19.17 s ClockTime = 19 s

Time = 4

Courant Number mean: 71.8097 max: 4.08253e+006
DILUPBiCG: Solving for Ux, Initial residual = 0.931317, Final residual = 0.0607
204, No Iterations 2
DILUPBiCG: Solving for Uy, Initial residual = 0.822577, Final residual = 0.0342
344, No Iterations 2
DILUPBiCG: Solving for Uz, Initial residual = 0.910466, Final residual = 0.0371
86, No Iterations 2
DICPCG: Solving for p, Initial residual = 0.998214, Final residual = 0.00879498
, No Iterations 71
time step continuity errors : sum local = 10.4873, global = 4.33564, cumulative
= 4.33431
DICPCG: Solving for p, Initial residual = 0.0379911, Final residual = 9.28994e-
007, No Iterations 135
time step continuity errors : sum local = 1862.64, global = 494.993, cumulative
= 499.327
DILUPBiCG: Solving for epsilon, Initial residual = 0.999319, Final residual = 6
.48079, No Iterations 1001
bounding epsilon, min: -8.20939e+015 max: 6.91709e+015 average: -1.10719e+012
DILUPBiCG: Solving for k, Initial residual = 0.0116847, Final residual = 0.0758
928, No Iterations 1001
bounding k, min: -1.30958e+015 max: 1.33593e+015 average: 9.7251e+010
ExecutionTime = 110.045 s ClockTime = 110 s

Time = 5

Courant Number mean: 7.30475e+008 max: 1.14002e+014
DILUPBiCG: Solving for Ux, Initial residual = 0.850483, Final residual = 0.0704
834, No Iterations 1
DILUPBiCG: Solving for Uy, Initial residual = 0.807872, Final residual = 0.0769
487, No Iterations 1
DILUPBiCG: Solving for Uz, Initial residual = 0.927567, Final residual = 0.0562
261, No Iterations 1
DICPCG: Solving for p, Initial residual = 0.999788, Final residual = 94280.9, N
o Iterations 1001
time step continuity errors : sum local = 2.01679e+016, global = -2.17307e+014,
cumulative = -2.17307e+014
DICPCG: Solving for p, Initial residual = 1.69848e-005, Final residual = 0.0002
58383, No Iterations 1001
time step continuity errors : sum local = 1.07146e+034, global = 1.19886e+032, c
umulative = 1.19886e+032
DILUPBiCG: Solving for epsilon, Initial residual = 1, Final residual = 8.74346e
+014, No Iterations 1001
bounding epsilon, min: -8.96533e+067 max: 1.50189e+067 average: -6.53566e+062
DILUPBiCG: Solving for k, Initial residual = 1.08791e-010, Final residual = 1.0
8791e-010, No Iterations 0
ExecutionTime = 192.418 s ClockTime = 192 s

Time = 6

Courant Number mean: 1.61566e+034 max: 3.84916e+039

C:\piso>

I looked at a couple of other threads that might have a similar problem, and noticed one about the courant number going crazy, which seems to be the same here.

the above test was on a simple cube case and should have no meshing issues as far as I can tell.

If anyone has any ideas what might be the problem I would really appreciate some help.

Thanks very much in advance,

Andrew

[Solo Sails]

Ahh,

I have just tried the same case with no object (it was a cube) and it runs fine, so guess there must be a problem with the mesh.

Still, I am confused why a case that works with simplefoam would not work with Piso?

Any ideas?

Sorry to be so vague!

Andrew

[akidess]

To me it looks like your timestep is way too big. With PISO, you need smaller timesteps than with SIMPLE. Keep the maximum Courant number under 1 (i.e. reduce the time step from 1 to 0.01), and things should work better.

[Solo Sails]

As simple as that!

Thank you so much, you have just sorted a small problem for most, a massive problem for me!

Thanks again.

Andrew