[Kosdalak]

Hello,

After a few weeks of trouble, searching for (and often finding) some help here, I finally got my simulation to work. But it runs not very stable and also the results are not quite good. So maybe there are still some mistakes.

My case:
I got a ripped, square channel with cyclic BC with Re=50,000. I want to compare some RANS models, namely the RSM (SSG & LRR) with the k-w-SST and the v2f Model.

To keep this thread relativly short, I want to discuss here only the RSM. The BC at the walls for k, epsilon, nut and p are zeroGradient; for U noSlip and for R (0 0 0 0 0 0).
I started with a quick pre-simulation using the k-epsilon Model and afterwards calculated R. After a stable setting for starting my RSM Run, I switched to more accurate options. These "Control Files" are attached. Because my mesh got around 400 cells with a non-orthonognality of 77, I run some extra iterations. My mesh got in total around 2.2 million cells, so in total the mesh is in a good setting and my y+ for the "first" cell above each surface is around 1.
My timestep is pretty small but thats the only way to get mean Courant number less than 0.8 - even with a max. Courant number of around 9.


Also my residuals behave in a strange kind.



After 20,000 iterations the results for the velocity fields didn't changed even I'm calculating a transient (pisoFoam). And here is the reason for this thread:




--> What could be the reason for the strange velocity results?

• Could it be that my timestep is to small, so the Solver "creates" a steady-state case? (So far I'm not able to increase it, otherwise it crashes because of the Courant number)
• Are my control files "wrong"? Like my Schemes/Solver I'm using wrong? (My knowledge about the mathematics is not quite good. I found some post/information, telling me these are stable and accurate at the same time)
• Do you have some ideas or experience or just some hints for me?

The results for the velocity would be good if I had averaged them over some iterations. But as a result for just one timestep I think these are wrong.





I appreciate all kind of help and wish every reader a happy new year! If you need more information from me, don't hesitate to ask.
Greetings,
Jan