A feature added in Siemens Simcenter STAR CCM+ 2021.2 allows the fluid film to be used in combination with the Automatic Mesh Refinement (AMR) physics model.
For the simulation of the waterslide, we did just that. On the top of the waterslide water enters the domain with a mass flow rate of 40kg/s. This initially creates a thin fluid film on the bottom of the top basin, after which it flows into the waterslide itself. As the fluid film exceeds a volume fraction of water of more than 0.8 in the first cell on the surface of the waterslide, the fluid film phase is converted to a Volume of Fluid (VOF) water phase.

Once the VOF water phase activates the free surface AMR model will activate as well. In this case the mesh cells at the interface between the two VOF phases (water and air) is refined to better solve this interface.

Without refinement

With refinement

Would we model the fluid flow without AMR, then we would have to refine a much larger area since, at the start of the simulation, it is not known where the VOF water-air interface will be exactly. This would make the amount of mesh refinement needed prohibitive, significantly increasing the simulation time.
Using AMR in combination with the fluid film and VOF allows us to limit the simulation time, while still modelling the VOF layer precisely.