Self excited vibration analysis of a Rotor air ring bearing via a two degrees Of freedom approach

Abstract

Air-bearings are suitable for supporting high-speed, lightly loaded rotors for efficient transmission of energy. The use of air as compared to a conventional lubricant such as oil offers both advantages and disadvantages during air-bearing operation. The beneficial effect of low viscosity of air is a smaller heat generation rate due to viscous dissipation. Consequently, air-bearings operate with smaller thermally-induced stresses. The detrimental effect of low viscosity of air is a smaller damping capacity, which results in self-excited (SE) vibration. Most of the research attempts on air-bearings have been to analyze and evaluate this dynamic instability. newlineIn this thesis, an analysis of an externally-pressurized journal air-bearing (AB) with an air-ring (AR), or air-ring bearing (ARB), for a balanced, rigid, and light-weight rotor is reported. An elastic structure in the form of an AR is provided between the bearing-bushing and the casing. The dynamic coefficients (DC) of ARB are determined at various angular velocities and angular frequencies of vibration of the journal in its range of operation. These DC are then used to predict the dynamic stability of the rotor ARB system (RARBS) against SE vibration. A numerical simulation procedure is followed to determine the DC. newlineIn the previous studies to analyze and evaluate the dynamic instability of ARB: (1) Analysis for the pressure (p) distribution in the AB and AR regions were made by solving Reynolds equation (RE) separately in each region, and thereby their DC were determined separately newline