Supercritical Carbon Dioxide Lubricated Tilting-Pad Bearing: Frequency Perturbation Analysis and High-Frequency Limiting Characteristics

Abstract

Abstract. As supercritical carbon dioxide (S-CO2) Brayton cycles advance toward higher power densities, the lubrication and dynamic characteristics of support bearings are critical to the stability of turbine rotor systems. This article presents a numerical approach that combines the full-variable frequency perturbation method with the equivalent coefficient method to predict the equivalent dynamic stiffness and damping coefficients of S-CO2 tilting-pad bearings. The method captures the evolution of dynamic coefficients over the entire frequency range and determines their high-frequency limiting characteristics through a limiting process analysis. The limiting perturbation pressure solution shows that the high-frequency limiting coefficients are explicitly governed by the steady-state density ρ¯0 and the compressibility term ∂p¯ρ¯(p¯0,T¯0), which distinguish them from conventional gas-lubricated bearings. Furthermore, the effects of pad inertia, pivot offset ratio, static load configuration, and ambient parameters on bearing dynamics are systematically analyzed. The results show that S-CO2 tilting-pad bearings exhibit a characteristic stiffness hardening and damping vanishing behavior at high frequencies. Pad inertia reduces direct stiffness and amplifies cross-coupled stiffness at high frequencies, while enhancing damping near synchronous frequencies. Moreover, the influence of ambient parameters on the dynamic characteristics strongly depends on the thermodynamic region, with the pseudo-critical and stable supercritical zones showing distinct trends. The proposed approach offers an effective framework for analyzing the rotor dynamics and stability of S-CO2 turbine systems.