Compliant Hybrid Gas Bearing Using Integral Hermetically-Sealed Squeeze Film Dampers

The following paper focuses on an integral gas-film lubricated bearing concept developed to enable oil-free operation of super-critical carbon dioxide (sCO2) turbomachinery. The externally pressurized tilting pad bearing possesses a flexible bearing support with an integral hermetically sealed squeeze film damper. Unlike past concepts using modular hermetic squeeze film dampers, the bearing design in this work utilizes advanced manufacturing methods to yield an integral single piece design developed to reduce space envelope, cost, and improve design reliability. The paper advances a detailed description of the bearing design and identification of bearing support force coefficients. Non-rotating bench-top tests show the influence of vibration amplitude, frequency, and damper cavity pressurization on force coefficients for two different viscosity fluids. Results indicate an increase in stiffness and a decrease in damping when increasing the frequency of excitation. Damper cavity pressurization was shown to eliminate squeeze film cavitation for the vibration amplitudes and frequency range in the study. Additionally, the paper advances a transient fluid-structure interaction (FSI) analysis aimed at gaining insight on the interaction of flexible elements bounding a hermetic fluid volume experiencing sinusoidal vibratory motion. The analysis considers an idealized damper model with and without a vibration transmission post while varying diaphragm modulus of elasticity for three excitation frequencies. Computational results were able to capture the increase in stiffness and decrease in damping showing that the flexibility of the bounding elements influence the damper cavity volume change and phase; ultimately effecting dynamic cavity pressures and force coefficients.