Abstract: The start-up process of the high-speed turbopumps for the liquid rocket engine is a typical transient start-up process under the harsh conditions, such as high pressure and cryogenic, which easily leads to the failure of the support bearings. The lubrication model and the friction-torque model for expressing the start-up process of the cryogenic roll-bearing are constructed, and the fluid film pressure distribution and the minimum film thickness for the different rolling elements are obtained under the specific operating conditions. The start-up friction-torque of a specific cryogenic rolling bearing under the different loads and speeds is calculated, according to which a method for defining the minimum radial preload to ensure the bearing's safety in the transient start-up processing is proposed. Two sets of experimental tests for the rolling bearing under the transient start-up and cryogenic nitrogen condition are carried out, and the the dynamic responses of the bearing are obtained. The experimental results qualitatively verify the reasonablenes of the above defined minimum radial preload for the cryogenic bearing. The fast feature extraction results of the dynamic responses also indicate that the failure of the bearing in the start-up processing may come from a localized rubbing, or even from serious metal friction or scraping between the different bearing components. The study has an important theoretical and experimental value for improving the safe service performance of the high-speed turbopumps in the cryogenic liquid rocket engine.

Key words: cryogenic, rolling bearing, transient start-up process, lubrication model, dynamic responses