Stability of Squeeze-Film-Damper Supported Flexible Rotors

Abstract

Assuming the short bearing approximation and symmetric motions, the stability of the steady-state synchronous operation of centrally preloaded single-mass flexible rotors supported in squeeze-film bearing dampers is theoretically investigated. The stability regions are depicted over a wide range of system parameters and allow for easy determination of the stability of existing steady-state design data. The influence of rotor flexibility, rotor speed, bearing dimensions, lubricant viscosity, rotor mass distribution, and rotor unbalance on rotor-bearing system stability may be readily seen. In the absence of pressurization, instability regions were possible even with relatively high support damping, though no instability was indicated for speeds below the support natural frequency, or for bearing eccentricity ratio <0.4 at any speed. Pressurization of the lubricant supply was found to stabilize the system over the whole range of parameters investigated, regardless of unbalance, which would then be limited only by the bearing clearance. Data are presented which enable the minimum supply pressure to ensure full film lubrication to be conveniently determined.

A Study of Lubricant Inertia Effects for Squeeze Film Dampers Incorporated into High-Speed Turbomachinery

“…The simple flexible rotor model assumes that the total mass of the rotor is either concentrated in the center or in the middle plane of the rotor, or alternatively it is distributed between the rotor center of mass and the center of the bearings. The steady-state orbit whirls of a simple flexible rotor supported by SFDs was investigated in [40][41][42]. In many practical examples, the number of degrees of freedom (DOFs) represented by the simple flexible rotor model is insufficient to provide an accurate approximation of the system dynamics.…”

Experimental Evaluation of Squeeze Film Supported Flexible Rotors

“…These considerations imposed constraints on the design which were not easy to satisfy as the design analyses depend in a complicated manner on the unbalance parameter U, the bearing parameter B, the frequency ratio f, the mass ratio a and the speed parameter a. Several possible rig configurations which covered the relevant range of these parameters were conceived and are summarized in (14). Of these, only the second configuration, corresponding to a = 0.08 and f=0.5 was actually constructed.…”

“…schematically the general assembly. Important features of the design and the determination of its dimensions are discussed in (14). Fig.…”

“…0.05< B < 0.8,for both pressurized and unpressurized conditions. For pressurization, the lubricant supply pressure was kept at more than 1.2 times the theoretical pressure required to obtain a 27 film (13). After heating the oil (often for several hours) lubricant flow had to be maintained for over half an hour before steady state temperatures were obtained.…”

“…However, very little experimental data is available in the literature at speeds in the vicinity of the rotor critical speed. Hence, experimental investigation to test the theoretical results previously reported by the authors (11)(12)(13) was felt to be necessary.…”