Investigation of Windage Losses in Flywheel Energy Storage Systems under Low Vacuum Conditions

Flywheel Energy Storage Systems (FESS), as a mechanical energy storage method, offer broad application prospects due to their high efficiency, rapid response, and long lifespan. However, challenges such as high costs and low energy density persist. This study leverages vacuum technology to effectively reduce windage losses in flywheel rotors and proposes a fluid-thermal coupled numerical simulation method for cross-scale vacuum systems involving flywheels and sealing rings. A vacuum test bench was constructed to validate the numerical method and the sealing performance of various sealing rings was evaluated. The research also examines the thermal effects of FESS under low vacuum conditions. Results indicate that traditional empirical formulas poorly predict windage losses under low vacuum conditions. The proposed model reveals distinct patterns in the exponential terms of windage losses on the flywheel’s cylindrical and end surfaces as pressure decreases and highlights the inhibitory effect of temperature rise. Furthermore, the study elucidates the influence mechanisms of velocity gradients and boundary layer thickness on windage losses and analyzes the impact of Taylor vortices in the flywheel gap under low vacuum on the distribution of surface losses. These findings provide a theoretical basis for optimizing FESS thermal management, enhancing system efficiency and reliability.