STUDY ON THE PREVENTION OF THE PAD FLUTTERING IN A TILTING PAD JOURNAL BEARING USING THE VARIATION OF PRELOAD

摘要

Fluid film tilting pad journal bearings are widely used for large steam turbines. However, bearing problems by pad fluttering, such as fatigue damage in the upper unloaded pad, the break of locking pins and the wear of pinholes etc., are frequently taken place in the actual steam turbines. The purpose of the present work is to investigate on the prevention of pad fluttering using the variation of preload(m) in a tilting pad journal bearing for steam turbines. It is estimated that upper pad is easily to flutter because the film shape of upper pad is divergent one from the analysis of moment direction acting on pivot point. Effective preload range in order to be statically loaded pad under all operating conditions is suggested as m > 0.5. Also, as a bearing that can be prevented pad fluttering, design modified bearing is suggested. For the adjustment in actual steam turbines, bearing and rotor dynamic analysis are performed to identify bearing characteristics and to verify the reliability of rotor-bearing system.