Aerodynamic Drag and Heating Effects on the Dynamics of a Vertical Rotor

This paper presents the rotordynamic modelling and analysis of a vertical rotor designed for a flywheel energy storage system (FESS) demonstrator. The study focuses on developing an analytical and semi-empirical model to predict the dynamic behaviour of the high-speed rotor. The modelling framework incorporates gyroscopic effects and bearing stiffness to evaluate critical speeds under varying operational conditions. Attention is given to the influence of aerodynamic drag and heating within a vacuum chamber, which remain significant at high rotational speeds. These aerodynamic losses and associated heating phenomena are embedded in the model, as they directly affect the system performance, material thermal constraints, and rotor stability. The study uses these effects to improve the overall energy retention capability of the system. In addition, a law governing the turbopump duty cycle is formulated to reduce parasitic power consumption during vacuum generation and thermal control. This duty cycle optimization is expressed as a function of the chamber pressure, heat generation rate, and rotor speed. Also, the combined rotordynamic and thermofluidic modelling provides an integrated understanding of the interactions within a family of rotating machines, offering a valuable guideline for the design of high-efficiency systems for energy-related applications.