[enoch]

I did not understand why the solution diverged even though Co was less than 1 and mesh quality of an expansion channel looked very good. (only hexahedral meshes used.) I confirmed that the solution converged using simpleFoam, but I have to use pisoFoam. Could you please how I can make the solution converged?

Solver: pisoFoam
time step: 0.00001








Time = 0.00127

Courant Number mean: 0.000311654 max: 0.050861
DILUPBiCG: Solving for Ux, Initial residual = 0.218313, Final residual = 5.69983e-06, No Iterations 7
DILUPBiCG: Solving for Uy, Initial residual = 0.629777, Final residual = 7.26245e-06, No Iterations 8
DILUPBiCG: Solving for Uz, Initial residual = 0.813262, Final residual = 4.59516e-06, No Iterations 9
DICPCG: Solving for p, Initial residual = 0.0588425, Final residual = 0.00573561, No Iterations 13
time step continuity errors : sum local = 1.09564e-06, global = 2.10204e-07, cumulative = 2.01415e-07
DICPCG: Solving for p, Initial residual = 0.0395018, Final residual = 9.25134e-07, No Iterations 832
time step continuity errors : sum local = 1.76973e-10, global = 2.61937e-13, cumulative = 2.01415e-07
ExecutionTime = 7006.28 s ClockTime = 7024 s

Time = 0.00128

Courant Number mean: 0.000312157 max: 0.0554556
DILUPBiCG: Solving for Ux, Initial residual = 0.502578, Final residual = 4.21354e-06, No Iterations 8
DILUPBiCG: Solving for Uy, Initial residual = 0.720687, Final residual = 4.78693e-06, No Iterations 9
DILUPBiCG: Solving for Uz, Initial residual = 0.817737, Final residual = 4.35604e-06, No Iterations 9
^C

===
checkMesh

/*---------------------------------------------------------------------------*\
| ========= | |
| \\ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \\ / O peration | Version: 2.1.0 |
| \\ / A nd | Web: www.OpenFOAM.org |
| \\/ M anipulation | |
\*---------------------------------------------------------------------------*/
Build : 2.1.0-0bc225064152
Exec : checkMesh
Date : May 16 2012
Time : 21:18:25
Host : "Aspire"
PID : 11943
Case : /home/OpenFOAM/jeong-2.1.0/run/pisoFoam/ras/expChannel
nProcs : 1
sigFpe : Enabling floating point exception trapping (FOAM_SIGFPE).
fileModificationChecking : Monitoring run-time modified files using timeStampMaster
allowSystemOperations : Allowing user-supplied system call operations

// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
Create time

Create polyMesh for time = 0

Time = 0

Mesh stats
points: 1286100
faces: 3718487
internal faces: 3581509
cells: 1216666
boundary patches: 3
point zones: 0
face zones: 0
cell zones: 0

Overall number of cells of each type:
hexahedra: 1216666
prisms: 0
wedges: 0
pyramids: 0
tet wedges: 0
tetrahedra: 0
polyhedra: 0

Checking topology...
Boundary definition OK.
Cell to face addressing OK.
Point usage OK.
Upper triangular ordering OK.
Face vertices OK.
Number of regions: 1 (OK).

Checking patch topology for multiply connected surfaces ...
Patch Faces Points Surface topology
WALL 134426 134572 ok (non-closed singly connected)
IN 841 900 ok (non-closed singly connected)
OUT 1711 1800 ok (non-closed singly connected)

Checking geometry...
Overall domain bounding box (-0.002 -0.0001 -3.46945e-21) (0.004 0.0001 0.0001)
Mesh (non-empty, non-wedge) directions (1 1 1)
Mesh (non-empty) directions (1 1 1)
Boundary openness (2.56678e-17 -7.99211e-15 -9.73591e-20) OK.
Max cell openness = 3.50175e-16 OK.
Max aspect ratio = 7.66351 OK.
Minumum face area = 9.68955e-13. Maximum face area = 4.58198e-11. Face area magnitudes OK.
Min volume = 9.68962e-19. Max volume = 2.44793e-16. Total volume = 1e-10. Cell volumes OK.
Mesh non-orthogonality Max: 0.526672 average: 0.0961124
Non-orthogonality check OK.
Face pyramids OK.
Max skewness = 3.0378 OK.
Coupled point location match (average 0) OK.

Mesh OK.

End