Experimental Validation on Reverse Precession in Foil Gas Bearing Supported Turbomachinery

Abstract Typical rotordynamic analysis of turbomachinery requires the identification of rigid body modes (RBM), bending critical speeds, and rotor orbit precession direction. Turbomachinery supported on hydrodynamic foil gas bearings (FGB) features a rotor-bearing system (RBS) designed to keep the RBM below the operating speed range. Adequate separation margins are required for 1st bending critical speed for a reliable turbomachinery operation. Identification of forward and reverse precession direction is also paramount during the design phase to ensure turbomachinery reliability. There is an abundance of literature published on reverse precession on turbomachinery supported on other types of bearings, such as rolling element and fluid film bearings. Reverse precession is seldom reported in real life on FGB-supported turbomachinery. This research paper aims to bridge this gap by providing information on reverse precession in FGB-supported turbomachinery. This research is motivated by the unexpected observance of consistent reverse precession during startup, steady state, and coast-down operation of FGB-supported motor-driven experimental turbomachinery in the research lab. This research delves into experimental observations about reverse precession corroborated by rotordynamic model predictions. It further explores the effect of FGB support structure stiffness anisotropy on reverse precession. This paper aims to provide a reference to future design engineers and researchers embarking on new turbomachinery RBS designs for challenging applications supported on hydrodynamic FGBs.