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.
Highlights
Rotor vibration problem of rotating machinery can be extremely frustrating and may lead to greatly reduced reliability. e factors causing rotor vibration are various, including but not limited to: poor stability of bearing system [1, 2], mass unbalance of rotor [3, 4], asymmetric loading and asymmetric aerodynamic forces [5, 6]
It results in rotor thermal bending, which leads to unstable vibration [7,8,9]. e previous studies mainly concentrate on rub between seals and sha
Morton effect is a synchronous vibration phenomenon that results from journal surface temperature difference caused by viscous shearing within lubricant film. e journal surface temperature difference results in temporary rotor thermal bending, which leads to an increase in rotor vibration. e journal surface temperature distribution in journal bearing is uniform in traditional views [13]
Summary
Rotor vibration problem of rotating machinery can be extremely frustrating and may lead to greatly reduced reliability. e factors causing rotor vibration are various, including but not limited to: poor stability of bearing system [1, 2], mass unbalance of rotor [3, 4], asymmetric loading and asymmetric aerodynamic forces [5, 6]. E asymmetric temperature difference appears on sha surface when rub occurs It results in rotor thermal bending, which leads to unstable vibration [7,8,9]. Morton effect is a synchronous vibration phenomenon that results from journal surface temperature difference caused by viscous shearing within lubricant film. Suh et al [17, 18] suggested that there is a large journal surface temperature difference when the journal whirls in journal bearing It causes temporary rotor thermal bending and leads to vibration instability of the rotor. Kirk et al [19] proposed an analysis model for overhung rotor to study the synchronous thermal instability caused by viscous shearing within the lubricant. An engineering vibration fault with its treatment is presented
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