Effects of Temperature on Nonlinear Dynamic Behavior of Gas Journal Bearing-rotor Systems for Microengine

ABSTRACT

The operating temperature of the gas bearings in a microengine can reach 1300–1700 K. The gas viscosity and the molecular mean free path both vary with changes in temperature, which influences the nonlinear dynamic characteristics of the gas journal bearing-rotor system. In this study, the molecular gas film lubrication model was extended to include the influence of temperature on both gas viscosity and molecular mean free path, systematically coupling the kinetic equations of the rotor to allow them to be solved simultaneously. The load-carrying capacity, center orbits, phase portraits, Poincaré maps, fast Fourier transform (FFT) spectra, bifurcation diagrams, and waterfall plots of the system response at various temperature points were investigated. As temperature increased, the resulting gas viscosity and molecular mean free path had conflicting impact on the load-carrying capacity of the system; the effect of the former was more significant, and higher operating temperature yielded stronger load-carrying capacity when rotational speed was fixed. Variations in gas viscosity as temperature increased caused low-frequency vibrations, most notably, the half-frequency whirl in the rotor, which may have been inhibited by increasing molecular free path (thus strengthening the gas rarefaction effect). In effect, higher temperatures caused the system to crash at a lower rotational speed.

KEYWORDS:

• Hydrodynamic lubrication
• journal bearings
• gas lubrication
• dynamic modelling
• high temperature
• bifurcation

Funding

This work was supported by the Research Foundation for Youth Scholars of Beijing Technology and Business University (No. QNJJ2014-21), the National Natural Science Foundation of China (Grant Nos. 51275046, 51305029), and the General Program of Science and Technology Development Project of Beijing Municipal Education Commission (KM201110011009).