Design optimization, construction, and testing of a hydraulic flywheel accumulator

The applications of fluid power technology in the U.S. are widespread and diverse. A primary disadvantage of fluid power systems is their low energy storage density. Flywheels are robust, aligning naturally with hydraulic systems’ strengths, and offer up to an order of magnitude higher specific energy than hydraulic accumulators. The hydraulic flywheel accumulator is a dual domain energy storage system that leverages complimentary characteristics of each domain. The system involves rotating a piston style accumulator about its axis to store kinetic energy as well as pneumatic energy. The pneumatic energy is stored in the inner radii of the flywheel which do not lend themselves to efficient kinetic energy storage. Also, the centrifugal effects on the fluid will tend to mitigate the pressure dependent state of charge issue of traditional pneumatic accumulators. In this study, such a system is modeled and optimized for laboratory scale, constructed, and tested in a laboratory hardware-in-the-loop hydraulic system. Through prototype construction and experimentation, the concept is shown to be feasible and the energy loss models are shown to accurately predict the system performance.