Study on Thermal Unstable Vibration of Rotor under Journal Whirl with Large Amplitude in Journal Bearing

Abstract

To investigate the thermal unstable vibration caused by journal whirls with large amplitude in journal bearing, an analysis model of lubricant film thickness is established. The journal surface temperature distribution is solved, and the reason for journal surface temperature difference appearance and its influence on rotor vibration are analyzed. Taking a turbogenerator as an example, the journal surface temperature difference and the induced rotor thermal bending under synchronous whirl in the bearing are calculated. Meanwhile, an engineering vibration fault with its treatment is presented. Results show that, the journal surface circumferential temperature difference is caused by viscous shearing within lubricant film under journal whirls with large amplitude in journal bearing. The direction of temperature difference is related to the direction of unbalanced force acting on journal. The temperature difference causes rotor thermal bending, which can be converted to a thermal unbalance on the rotor. The rotor vibration is caused by both thermal and initial unbalance. When the rotor is running below or at the critical speed, the vibration is on the increase until it leads to instability of the rotor eventually. When the rotor is running above the critical speed, the rotor vibration fluctuates periodically. Reducing the initial (mechanical) unbalances decreases the rotor vibration and the journal surface circumferential temperature difference.

Simulation of heat transfer in a turbocharger bearing housing

“…Research [6] is devoted to the study of the influence of the thermal imbalance of the rotor on the oscillation amplitudes of the turbine generator bearings. The temperature difference causes a thermal bending of the rotor, which is converted into a thermal imbalance.…”

“…In recent years, the number of works devoted to unstable vibrations caused by uneven heating of the rotor has been growing [6][7][8]. The thickness of the lubricating layer differs depending on the local area, due to which the values of hydraulic losses differ.…”

Non-uniform flow and heat transfer characteristics and parametric study of generator hydrogen double-flow ring seal

“…In addition to the important influence of physical properties and heat transfer models on the temperature and pressure distribution of lubricating oil films mentioned above, some studies have shown that the existence of circumferential eccentric gap can cause non-uniform distribution of circumferential pressure and velocity due to its fixed clearance cylindrical seal [13,14] , floating ring seal [15,16]and bearing [17]. It is pointed out that the existence of circumferential eccentric clearance will lead to the non-uniformity of circumferential temperature, and will further lead to the unbalanced vibration problem [18][19][20][21], which is called Morton effect in oil-lubricated journal bearings [22], and a similar phenomenon may occur in floating ring seal. However, the nonuniformity of circumferential temperature caused by the eccentric clearance of the floating ring seal developed from the hydrodynamic journal bearing may also be an important reason for the vibration of the hydrogen-cooled generator [23,24].…”