Design and fabrication of hybrid composite hubs for a multi-rim flywheel energy storage system

A composite hub was successfully designed and fabricated for a flywheel rotor of 51 kWh energy storage capacities. To be compatible with a rotor, designed to expand by 1% hoop strain at a maximum rotational speed of 15,000 rpm, the hub was flexible enough in the radial direction to deform together with the inner rotor surface. This hub is also stiff in the conical deformation mode to increase the vibration frequency for high rotational speed. A dome type hub of carbon-glass/epoxy has been developed to be press-fitted into the rotor with interference in order to offset the hoop strain. A series of parametric study were sequentially performed to determine fiber fractions, layer thickness, winding angles, interference, and the shape of the geodesic dome contour. A safety factor of two was secured in the final design to take into consideration a long term fatigue life of the hub. The hub was fabricated by wet filament windingprocess, followed by press-fitting into a surrogated rotor, which has the same inner and outer diameters and stress states as those of original rotor except height. The strains were measured during the press-fit and found to be in agreement with the stress analysis results.