I’ve been fascinated with fish passages for a long time, and always wanted to simulate one. Unfortunately, the couple of proposals I presented for different projects in the past few years were not picked up.
This weekend I had one of the workstations available and decided to go for it. I sketched a simple geometry on CAD and implemented an OpenFOAM model. I only simulated three chambers to keep computational costs low enough; typical fish ladders include many more.
I went for a Delayed Detached Eddy Simulation (DDES) turbulence treatment to better capture the flow instabilities in the chambers. DDES balances accuracy and computational efficiency by using a combination of Reynolds-Averaged Navier-Stokes (RANS) turbulence modeling and Large Eddy Simulation (LES) turbulence modeling. In DDES, the turbulence is resolved at large length scales, in places where the mesh is fine enough, and modeled at smaller scales. This approach allows for a more accurate representation of turbulence behavior while reducing computational costs compared to traditional LES.
The model has a couple of interesting features, including a fixed water level boundary condition, achieved by fixing the pressure (p_rgh) on all the wetted faces.
If you are curious, I have uploaded the source code for this case to GitHub: