Extremely Small Time step to Maintain Courant Number of 10
 

I am running a komegasst simulation in parallel containing 4 million elements. I made my mesh using ansys meshing software and below is the checkMesh results:
Mesh stats
points: 2076394
internal points: 1949842
faces: 12198649
internal faces: 11945553
cells: 5177068
faces per cell: 4.66368
boundary patches: 4
point zones: 0
face zones: 1
cell zones: 1

Overall number of cells of each type:
hexahedra: 0
prisms: 3435930
wedges: 0
pyramids: 0
tet wedges: 0
tetrahedra: 1741138
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
inlet 2238 1186 ok (non-closed singly connected)
outlet 2238 1186 ok (non-closed singly connected)
wall 19558 9911 ok (non-closed singly connected)
cube 229062 114533 ok (closed singly connected)

Checking geometry...
Overall domain bounding box (-1.09 -1.01797 -2.75) (1.09 1.0272 1.75)
Mesh has 3 geometric (non-empty/wedge) directions (1 1 1)
Mesh has 3 solution (non-empty) directions (1 1 1)
Boundary openness (-3.05175e-16 6.10809e-16 -3.99538e-17) OK.
Max cell openness = 6.63526e-16 OK.
Max aspect ratio = 20.153 OK.
Minimum face area = 3.21818e-08. Maximum face area = 0.0145499. Face area magnitudes OK.
Min volume = 1.00001e-11. Max volume = 0.000502156. Total volume = 20.0617. Cell volumes OK.
Mesh non-orthogonality Max: 62.8113 average: 12.8053
Non-orthogonality check OK.
Face pyramids OK.
Max skewness = 2.47308 OK.
Coupled point location match (average 0) OK.

Mesh OK.

End



In controlDict I specified that I need a courant number below 10 and openFoam corrects it. Except to have a courant number of 10, my time steps are around 1e-53 and then the last one is 1e-108 and the program throws a floating point error.
If someone minds taking a look that would be great. Thanks!
I can upload my files to if needed.

Why are you going for 10?
Your simulation is probably just diverging, with velocities over 1e50.
Then, the dynamic Courant criterion demands that your timestep is less than 1e-53 (of course, depending on your cell sizes).

Try maxCo=0.5, and see what happens.

Co>1 is unstable. The only way to perform those kind of simulations is with heavy under-relaxation and possibly some other tricks.

Which solver are you using? Do you use underrelaxation?

I am using pimple foam and my underelaxation values are .7 on U and .3 on everything else.

Hello Everyone!

My calculation is converging evey time, and my courant number are as follows:

Global Courant Number [Variable Time Step Criteria] : 0.07

Global Courant Number [Explicit VOF Criteria] : 0.01

I am running my simulation on HPC cluster. Are those value good to have a flow ??

Thank you in advance!