Substantiating the optimal shape of a bimetal flywheel

This study’s object is the flywheel as an energy storage device. The task addressed is to devise a sequential approach to flywheel shape optimization. The analytical basis of flywheel shape optimization has been reconstructed to reveal the source of contradictory results. It was found that the product of radius and angular velocity of rotation is a constant that depends on material properties for the ring-shaped disk flywheel. It becomes somewhat more complicated for other flywheel shapes. It is the reason for the contradictions in the flywheel shape optimization results reported by researchers. Comparative calculations for several flywheel shapes have been performed using the finite element method. The results confirmed that bringing material closer to the axis of rotation, including Laval disk shape, does not give any advantages. Material choice has an essential advantage in comparison with shape optimization. The flywheel shape has to be optimized together with the material. A ring-shaped disk flywheel is a good starting point for flywheel shape optimization. The results are attributed to the nature of the flywheel material behavior under the action of inertia forces. A novel approach to combining different materials in flywheel construction has been proposed. One material (high-strength steel) was used for the flywheel ring. Another material with a lower elastic modulus (high-strength aluminum alloy) was used for elements connecting the ring with the shaft. The bimetal flywheel has a mass three times less than the base variant, with 24.6% underload for steel parts and 17.3% underload for aluminum parts. The findings reported here could be practically implemented in the design and manufacturing of flywheel energy storage systems with increased specific energy for use in vehicles and stationary power units