Construction and Experimental Application of a Variable Geometry Journal Bearing (VGJB) for the Vibration Suppression of Rotors

Abstract

A journal bearing with variable geometry (VGJB) was proposed and its operating principle was investigated theoretically in previous works showing a promising impact on the vibration quenching of simple and more complicated rotor bearing system during the passage through the first critical speed. The journal bearing with variable geometry is presented in this paper in its final form with the detailed design and manufacturing procedure. The current journal bearing was constructed in order to be applied in a simple experimental rotor bearing system composed by a Jeffcott rotor mounted on one plain cylindrical journal bearing and one VGJB. The inspiration for the current idea is based on the fact that the alteration of the fluid film characteristics of stiffness and damping during the passage through resonance results in vibration quenching [1]. This alteration of the bearing characteristics is achieved by the introduction of an additional fluid film thickness using the passive displacement of the lower half-bearing part. The influence of the additional fluid film to the characteristics of journal bearings has been investigated because of wear phenomena that appear often in plain journal bearings [2–4]. The applicability of the current journal bearing can contribute towards the vibration amplitude reduction of high scale rotor bearing systems where the resonance amplitude during the passage through resonance is a matter of consideration because of its influence in the foundation and the surrounding environment of the rotational system [5]. In the presented experimental application, the developed resonance amplitude is reduced at about 40 % compared to the system with normal journal bearings. The diagrams of amplitude with respect to the rotational speed during the start up of the system prove the reduction of the vibration amplitude while diagrams of the operational characteristics of the journal bearing are also presented. The VGJB is a totally passively activated subsystem that has to be tuned with respect to the fluid film pressure that is developed in the journal bearings during the passage through resonance. The damping and spring elements that consists of the operational mechanism of the journal bearing with variable geometry are presented in detail. In contrast to the many suggested damping mechanisms for the vibration quenching of rotor bearing systems, the present journal bearing does not add damping properties in the system but it alters the stiffness and damping properties of the fluid film in the specific time duration during the passage through resonance.