Stability and Stability Degree of a Cracked Flexible Rotor Supported on Journal Bearings

Abstract

This paper investigates the stability and the stability degree of a cracked flexible rotor supported on different kinds of journal bearings. It is found that no matter what kinds of bearings are used, the unstable zones caused by rotor crack locate always within the speed ratio of 2/N(1−ΔKξ /4)<Ω<2/N when gravity parameter Wg>1.0; and locate always within the speed ratio of 2Ωα/N(1−ΔKξ /4)<Ω<2Ωα/N when Wg<0.1, where ΔKξ is the crack stiffness ratio, N=1,2,3,4,5,[[ellipsis]] and Ωα=(1+1/2α)1/2. When 0.1<Wg<1.0, there is a region where no unstable zones caused by rotor crack exist. Outside the crack ridge zones, the rotor crack has almost no influence on the system’s stability and stability degree; while within the crack ridge zones, the stability and the stability degree depend both on the crack and the system’s parameters. In some cases, the system may still be stable even though the crack is very large. For small gravity parameter (Wg<0.1), the mass ratio α has a large influence on the position of the unstable region, but its influence on the stability degree is small. The influence of fixed Sommerfeld number So on the stability degree of the cracked rotor is small, although So has a large influence on the stability degree of the uncracked rotor. [S0739-3717(00)70502-2]