Reduction of mechanical loss of flywheel energy storage system with spherical spiral groove bearing

Flywheel Energy Storage System (FESS) is known as a mechanical battery to store electricity. In a small-scale FESS, mechanical loss due to frictions of bearings must be reduced. In this study, a Spherical Spiral Groove Bearing (SSGB) is used to reduce the bearing loss. The bearing performance of SSGB is greatly affected by the groove shape, therefore the aim of this paper is to optimize the groove shape by means of computational fluid dynamics (CFD). CFD simulation results show that the groove width ratio Δ and groove depth h0 have dominant effects on the bearing performance; and that the bearing loss can be reduced by 36.5% with Δ = 0.70 and h0 = 0.02 mm as compared to the SSGB currently used. The prototype SSGB with the optimized shape was fabricated and the actual bearing loss was experimentally tested. As a result, it was confirmed that the bearing loss was reduced by 37.8 %.