I remember a video of a very small hydro power demo, about a meter across, something along the lines of a gravitational water vortex power plant[0], but instead of the usual turbine they had a pretty big, uh, piece ("runner"?) in the middle of the chamber with the vortex, taking up most of the space. I believe the idea was to extract energy from very low flows. I seem to recall the people presenting it were Swiss, or something else vaguely germanic, but I'm not really sure.

Anyway, I've thought about this thing for years, decided to try to find it again, and mostly failed in my google-fu. I don't remember anything of the specific language used to describe it, just the visual. If anyone knows good search terms for this, I'm happy to hear those as well.

Thanks!

[0] https://en.wikipedia.org/wiki/Gravitation_water_vortex_power_plant, discussed here https://news.ycombinator.com/item?id=16891441