The rolling fluid turbine is a bladeless hydraulic device that exhibits peculiar behavior, making it interesting from the aspect of fluid dynamics. The rotor of this turbine has an unusually symmetrical shape and can rotate in two directions---the one it ''chooses"" seems to be random.
Explanation of the underlying hydraulic mechanism is an open problem, which we tackle here. This paper suggests that the hydraulic force on the rotor acts as positive feedback on the motion of the rotor itself.
Such an effect can exist since the system is thermodynamically open. Power generation is described in an analytical computation based mostly on the arguments of symmetry.
The result is then tested in a numerical simulation.