Moving from simpleFoam to interFoam with alpha = 0
 

Dear experts,

In the approach to a two-phase case, I have successfully set up a single-phase case using simpleFoam. This runs perfectly. But, when adapting to interFoam - still in single phase for starters setting alpha = 0 - the Courant numbers truly explodes in just 3-4 tiny time steps. I am aware that the simpleFoam is steady state and the interFoam not, but is there another way to adjust the interFoam (and in the end compressibleInterFoam) so that the simulation will run more smoothly? Though, I am afraid that my mesh - being imported from CFX - has some quite small cell sizes ... but why doesn't that affect the steadyState solution?

From checkMesh:

Mesh stats
points: 21113
faces: 115526
internal faces: 104294
cells: 47382
boundary patches: 4
point zones: 0
face zones: 1
cell zones: 1

Overall number of cells of each type:
hexahedra: 0
prisms: 28902
wedges: 0
pyramids: 1390
tet wedges: 0
tetrahedra: 17090
polyhedra: 0

Checking topology...
Boundary definition 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
ut 124 117 ok (non-closed singly connected)
inn 124 117 ok (non-closed singly connected)
air 318 259 ok (non-closed singly connected)
default_2d_region 10666 5431 ok (non-closed singly connected)

Checking geometry...
Overall domain bounding box (-0.236336 -0.239982 -2.4) (0.7 0.239982 0.4)
Mesh (non-empty, non-wedge) directions (1 1 1)
Mesh (non-empty) directions (1 1 1)
Boundary openness (1.13037e-18 -1.18054e-18 -9.22588e-20) OK.
Max cell openness = 2.96835e-16 OK.
Max aspect ratio = 16.9272 OK.
Minumum face area = 3.7315e-08. Maximum face area = 0.00757382. Face area magnitudes OK.
Min volume = 3.83728e-12. Max volume = 0.000199136. Total volume = 0.229311. Cell volumes OK.
Mesh non-orthogonality Max: 78.5452 average: 17.3679
*Number of severely non-orthogonal faces: 60.
Non-orthogonality check OK.
<<Writing 60 non-orthogonal faces to set nonOrthoFaces
Face pyramids OK.
Max skewness = 1.46116 OK.

Mesh OK.

Hi, dear Kjetil, I think the Max skewness of your mesh is a little big, it is suggested to be less than 0.8 by some Foamers. However, in my experiences, about 0.9 is also OK. I am not sure about the concrete limit.
I think you can try to run your case in the pisoFoam, which is transient solver, maybe more similar to the interFoam considering one phase.
Best regards,
Chiven