Run up simulation of a full-floating ring supported Jeffcott-rotor considering two-phase flow cavitation
- PDF / 2,119,520 Bytes
- 14 Pages / 595.276 x 790.866 pts Page_size
- 52 Downloads / 164 Views
REVIEW
Christian Ziese
· Steffen Nitzschke · Elmar Woschke
Run up simulation of a full-floating ring supported Jeffcott-rotor considering two-phase flow cavitation
Received: 6 May 2020 / Accepted: 26 August 2020 © The Author(s) 2020
Abstract Hydrodynamic bearings are commonly used to support fast rotating rotors. Due to their nonlinear bearing properties, they strongly influence the rotor response behaviour, which can be observed by the occurrence of sub-harmonic oscillations. The appearance of sub-synchronous vibrations depends on the operating bearing conditions, which are determined by the kinematics of bearing partners, the thermodynamic processes and especially the occurrence of cavitation. In this contribution, the rotor response behaviour of a full-floating ring supported Jeffcott-rotor is investigated under the consideration of lubricant film cavitation. The two-phase model is applied as a mass-conserving cavitation theory and compared with the assumptions of Half-Sommerfeld. Keywords Run up simulation · Jeffcott-rotor · Full-floating ring bearing · Two-phase flow cavitation
1 Introduction Hydrodynamic bearings are preferentially used to support rotors, such as in exhaust gas turbochargers, stationary operating aggregates and turbine constructions. In terms of design, the bearing consists of a lubricant filled gap, whose surface is limited by shaft and housing. The aim of bearing design is therefore to define the gap geometry in such a way that sufficient lubricant fraction is ensured. Compared to rolling bearing assemblies, hydrodynamic bearings are more cost-effective, have a simpler design and more favourable thermohydrodynamic operating conditions. Furthermore, hydrodynamic bearings are classified into journal bearings and floating-ring bearings, whereby the first one has only one lubricating film, whereas the latter consists of two radially separated oil films. The lubricant exchange between inner and outer gap is achieved via connecting channels. The advantage of floating rings becomes clear when the lubricant film is considered from a thermodynamic point of view. The main purpose for using floating rings is the reduction of heat generation in bearings by decreasing the shear rate of the individual lubricating films. The thermo-hydrodynamic operating conditions have a significant influence on the rotor vibration behaviour, which can be observed by the occurrence of lubricant-film-induced excitations as sub-synchronous oscillations. On the other hand, the rotor can be excited via two lubricating films, which can lead to unstable response behaviour [1]. For journal bearings, the rotor is only excited via one lubricant film. Due to the nonlinear bearing properties, both unbalance induced synchronous vibrations and lubricant filminduced sub-synchronous rotor responses can occur, which are known as oil-whirl and oil-whip phenomena. The oil-whirl is defined as half-whirl frequency of oil, which correlates with the lubricant transport into the narrowing gap. In [2,3] is shown that the whirling frequenc
Data Loading...
