Nonlinear Dynamic Characteristics of Three-Pad Fluid Foil Bearing-Rotor System for Liquid Rocket Turbopumps

With the continuous development of reusable liquid rocket turbopumps, the conflict between high rotational speed operation and long service life requirements in traditional rolling bearing support schemes has became increasingly prominent. Fluid film bearing alternatives have emerged as one of the key technical upgrade approaches. Given the stability advantages of multi-pad foil bearings, the application feasibility of three-pad foil bearings under the low-temperature low-viscosity fluid environment of rocket turbopumps was theoretically evaluated in this study. Liquid nitrogen was used to simulate the rocket’s liquid working medium, and a time-domain dynamic model was established by coupling the four-degree-of-freedom rotor motion equations, the Reynolds lubrication equation, and the foil deformation equation. The nonlinear response characteristics of the three-pad fluid foil bearing rotor system were analyzed using rotor orbit diagrams, FFT plots, Poincaré maps, and bifurcation diagrams. The results indicated that subsynchronous vibrations were closely related to the structural parameters of the three-pad fluid foil bearing. By adjusting parameters such as unbalance and preload radius, stable operation of bearing-rotor system under various condition could be ensured. The relevant theoretical explorations could provide a valuable reference for developing novel fluid film bearing solutions for reusable rocket turbopumps.