The Thermal Unbalance Effect Induced by a Journal Bearing in Rigid and Flexible Rotors: Experimental Analysis

TL;DR

This study experimentally investigates how thermal unbalance affects rigid and flexible rotors supported by journal bearings, revealing amplitude increases, hysteresis effects, and instability triggers related to temperature differences and start-up procedures.

Contribution

It provides new experimental insights into thermal unbalance effects on rotor dynamics, including instability conditions and temperature-related phenomena.

Findings

Thermal unbalance increases synchronous amplitudes.

Hysteresis indicates amplitude increase due to thermal effects.

Shorter start-up times can trigger instability and bearing contact.

Abstract

The present work presents the experimental analyses of a rigid (short) and a flexible (long) rotor subject to thermal unbalance effects. The rotors are supported by a ball bearing and by a cylindrical journal bearing. The differential heating generated in the journal bearing is responsible for the thermal unbalance. The results obtained with the short rotor at 7 krpm showed an increase in the synchronous amplitudes but slight phase changes before stabilization. The pronounced hysteresis of the synchronous amplitudes obtained during coast-down proved that the amplitude increase is due to the thermal unbalance. The results obtained for the long rotor at 6.6 krpm showed the same stabilized response when start-up was performed in 180___s. However, an instability leading to journal bearing contact was triggered when the start-up time was decreased to 80___s. The presented experimental results are the synchronous amplitudes and phases, the mean temperatures, and the maximum temperature differences of the journal and of the bearing and the phase lags between the high spot and the hot spot.