(I don't know if there's a name for it, i've searched and i've never seen anyone mention this design)
I created a beast, and though all my senses tell me I should destroy it before it destroys us I feel I must share it.
I made this for my fort Daggerdepths, but I knew id fail miserably trying to get a large, working water reactor built the first time so I made this on a throwaway fort. It took about 10 game years to design, construct and optimized, tearing down and rebuilding whole sections 4 times so that it would work right. Hence when you look at the screenshots, it looks like a Frankenstein construction and appears it could blow apart and kill everyone at any time.
I have a reserved spot in my fortress with limited space, so it was built the way it is out of necessity. It was actually a fun challenge to fit the most powerful reactor I could make into a pre-defined area and i'd recommend others to try. I bet it would be a great challenge thread actually. If you might be interested let me know here.
Over-Under sounds appropriate because the water flows over and under the waterwheels to generate power.
This particular reactor consists of 153 waterwheels split into 9 stacked reactors, 17 waterwheels each linked to each other, 5 on the top and 4 on the bottom. Originally there were 11 reactors with 15 wheels each, but water flow didnt agree with it. 17 pumpstacks are needed to move the water with 34 screwpumps total. These are all linked to the main reactor, totaling a 1951 power requirement just to get the thing running.
Originally I was going to keep them separate and instead let 2 perpetual v-reactors or another of my own design run the pumps so that I only needed to pull a lever to turn the main reactor on. But then I didnt really want a reactor constantly running, it would hit my FPS and eventually stop running due to evaporation. It turned out that 2 dwarves can get it running quite easily, so i'll stick to that method.
The highlighted area on the third level is what i'm really proud of. I was having trouble keeping the water level high enough to turn the waterwheels in a couple sections so I put those pillars there to funnel higher volumes of water between them. It's still not perfect, it could use some tweaking but I think if perfected it could open the door for much larger wide-flow reactors and eliminate the low-flow problems they run into.
Onto more numbers. The 153 waterwheels have the potential to output 15,300 units of power, but i've only been able to manage to average around 12,000 units. Sometimes if the flow is bad it will dip below 10,000, but other times when the flow is good...
That's the highest power output i've witnessed. It might be able to go higher, not sure.
What's a little disconcerning is for several minutes after I first saw that it worked and was imagining all the dwarfy things I could do with this much power, Darth Vader music was playing in my head and I didn't even realize it. DF does awesome things to your brain. And Star Wars of course.
Some say perpetual motion machines are exploity, but with the amount of time and !!science!! that went into this, it probably would have been alot easier to draw power from a natural river XD.