Abstract: The discrete model of liquid hydrogen (LH₂) turbopump rotor is established using the finite element method. A two degrees of freedom model of ball bearing is presented for investigating the dynamic properties of the LH₂ turbopump rotor system supported by ball bearings. The model includes the effect of bearing internal clearance, bearing running surface waviness and ball centrifugal force. Thus, the ball bearings-LH₂ turbopump rotor system is modeled according to the discrete rotor model and the ball bearing model. The nonlinear dynamic characteristics in the start-up process are analyzed because the rotordynamic problems are concentrated in this process. Numerical results show that the subharmonic resonance as well as synchroresonance occurs in the start-up process. The radial load plays a significant role of the appearance of the subharmonic resonance and synchroresonance. The effects of ball centrifugal force and waviness are considerable.

Key words: turbopump, ball bearing, rotor, rocket engine, nonlinear vibration