[robboflea]

Hi all,

I'm trying to model transition on a 2D turbine airfoil by using the mesh in the picure. Basically two of the blocks in the boundary layer have been moved to a "LAMINAR" part in ICEM while the remaining part is in the "FLUID" part. The idea is to have the laminar zone to be set-up as a "laminar zone" in the cell zone conditions tab in Fluent, while running the simulation with fully turbulent Spalart Allmaras model. (I know I could use a transition model but I really want to try to tackle the problem in this way and I read somewhere in the forum that it was possible to do it but it was not explained well how).

All mesh check in ICEM works fine and I can import the mesh successfully in fluent. together with the normal inlet, outlet, blade and periodic boundaries I get also a boundary between the turbulent and laminar zones (set as an internal boundary) and a laminar wall boundary on the blade which I set as a normal wall.

The problem is that I can initialize the solution but I cannot start the solver. Using the same exact mesh (with the laminar patch being part of the fluid and the solver fully turbulent) I could run it without problems. Normally I used fmg initialization and then I run the case. Now when I run the fmg i get the following:

>> Reordering domain using Reverse Cuthill-McKee method:
zones, cells, faces, done.
Bandwidth reduction = 159/159 = 1.00
Done.

Creating multigrid levels...
Grid Level 0: 49126 cells, 98574 faces, 49900 nodes; 2 clusters
Grid Level 1: 12217 cells, 49704 faces, 0 nodes; 2 clusters
Grid Level 1: 12217 cells, 27317 faces, 0 nodes
Grid Level 2: 3532 cells, 27978 faces, 0 nodes; 2 clusters
Grid Level 2: 3532 cells, 9694 faces, 0 nodes
Grid Level 3: 1165 cells, 18093 faces, 0 nodes; 2 clusters
Grid Level 3: 1165 cells, 3500 faces, 0 nodes
Grid Level 4: 391 cells, 12094 faces, 0 nodes; 2 clusters
Grid Level 4: 391 cells, 1238 faces, 0 nodes
Grid Level 5: 135 cells, 8227 faces, 0 nodes; 2 clusters
Grid Level 5: 135 cells, 450 faces, 0 nodes
Done.


FMG: Converge FAS on level 5


FMG: Converge FAS on level 4


FMG: Converge FAS on level 3


FMG: Converge FAS on level 2


FMG: Converge FAS on level 1
0.->1.->2.->3.->4.->5.<<<<<

Error: Divergence detected in AMG solver: nut
Error Object: #f

Am I doing something wrong in the mesh generation or in Fluent setup?

Sorry for the long post.

Rob

[robboflea]

Apparently it was a Fluent bug. When restarting Fluent the day after everything was working fine.
If somebody needs help with this strategy for transition modeling I'll be happy to help.

Rob