Design and Spin Test of a Hybrid Composite Flywheel Rotor with a Split Type Hub

Abstract

A study is conducted on lowering the radial tensile stresses and increasing the performance of the fiber wound composite flywheel rotor by applying pressure on the inner surface of the rotor using a split type hub that spreads in the radial direction due to the centrifugal force. A conventional solid or ring type hub in most cases produces tensile stresses within the rotor, possibly causing delamination and eventually lowering the maximum speed of the rotor. The relationship between the stresses of the rotor and the thickness of the hub is derived and applied to the single and hybrid rotors. A hybrid composite rotor of 180 mm inner diameter and 340 mm outer diameter is designed and fabricated, which reaches only the strength ratio of 0.58 at the maximum rotating speed of 40,000 rpm. A spin test was conducted to show the improved performance of the rotor with the split type hub by measuring the mechanical strains from the rotor. The radial and circumferential strains at four different locations are measured up to 30,000 rpm using a wireless telemetry system, and they are in good agreement with the analytical calculations. The rotor has survived a spin test of up to 40,000 rpm, which corresponds to the usable energy of at least 500 W h with the safety factor of 1.7.

Flywheel Energy Storage for Automotive Applications

“…Space applications [103,104] Darmstads, Germany [105] Technical University of Dresden, Germany [106] Technical University of Eindhoven, TU/e, Netherlands [56] Hanyang University, Korea [107] Harbin Engineering University, China [108] Kyushu Institute of Technology Superconductive suspension [109,110] Nanjing University of Aeronautics and Astronautics, Nanjing, China…”

Rotor Design for High-Speed Flywheel Energy Storage Systems

“…This is accomplished by providing a compliant hub structure that due to the action of centrifugal forces superimposes compressive loading in the radial direction. Ha et al (2006) proposed a hub structure that is split at multiple locations along its length. Hub segments are therefore able to impose the desired radial compressive load on the inside of the rotor.…”

“…The method presented in this subsection generalizes DANFELT's approach in terms of its various extensions. Thorough validation of the method by means of FE analysis and experiments is given in references Ha et al (2003); Ha & Jeong (2005); Ha et al (2006). To the authors' knowledge all publications regarding analytical solutions to the described problem assume a constant rotational velocity.…”

“…It should be noted that the typically isotropic material behavior of a metallic hub can easily be modeled as a special case of transversal isotropy. A split-type hub was studied in reference Ha et al (2006). Therefore, the inner pressure was specified as the normal radial pressure caused by free expansion of the hub,…”

“…The optimization of the hub geometry connected to a two-rim glass/epoxy, carbon/epoxy rotor with r i = 120 mm and r o = 240 mm was examined for two common hub types: The conventional ring-type hub and the split-type hub as proposed in Ha et al (2006). The basic idea of the split-type hub is to interrupt the circumferential stress transmission by splitting up the hub into several segments, facilitating the radial expansion during rotation of the split-ring.…”