[finn_amann]

Hello friends,

first of all:
- OpenFOAM foundation version 9
- solver: interFoam
- tutorial case: /tutorials/multiphase/interFoam/RAS/weirOverflow

I'm trying to get more acquainted with turbulence modelling (still an absolute novice, but steadily learning). This is why I'm going through the tutorial cases of interFoam, specifically the case weirOverflow. In the case, 60 seconds of water flow over a weir are simulated. You can get a better grasp of the simulation from the images I attached, which show us t = 2s and t = 20s. You can also find the tutorial in path stated above and simulate the case yourself.

I ran the simulation with interFoam, including the k-Epsilon turbulence model. The simulation ran fine and exited after the 60s of simulation time were finished. The time step size is in the range of 5e-3.

Then I ran the simulation without turbulence in order to compare the two results. However, after simulating about 10 s of time, the time step decreased sharply (around 1e-10s), effectively preventing the simulation of the remaining time.

This raised some questions for me:
- Why does the time step decrease so sharply without turbulence?
- What could be changed to succesfully run the simulation as a laminar case? Of course, I've already dabbled in some changes in the fvSolution and fvSchemes, unsuccesfully, however.
- Is there some obvious hydrodynamic aspect I am missing here?
- Is there some obvious modelling aspect I've overlooked?


I'd love to hear some opinions on this.


Regards
Finn