DYNAMIC STABILITY OF OVERHUNG ROTOR PARTIALLY FILLED WITH LIQUID

1996 Fiscal Year Final Research Report Summary

• Project/Area Number: 07650289
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Dynamics/Control
• Research Institution: KYUSHU INSTITUTE OF TECHNOLOGY
• Principal Investigator: JINNOUCHI Yasusuke KYUSHU INSTITUTE OF TECHNOLOGY DEPARTMENT OF MECHANICAL ENGINEERING,PROFESSOR, 工学部, 教授 (10039092)
• Co-Investigator(Kenkyū-buntansha): INOUE Masanobu KYUSHU INSTITUTE OF TECHNOLOGY DEPARTMENT OF MECHANICAL ENGINEERING,ASSISTANT, 工学部, 助手 (70253549)
• Project Period (FY): 1995 – 1996
• Keywords: Flow-Induced Vibration / Self-Excited Vibration / Stability / Liquid Wave / Rotor Dynamics / Asynchronous whirl / Cenrifuge

Research Abstract

An investigation has been made into dynamic stability of a hollw cylindrical rotor mounted on an overhung shaft and containing liquid. A rigid rotor, mounted on an elastic shaft and containing a cylindrical cavity partially filled with liquid, often undergoes a strong asynchronous whirl under certain conditions. This phenomenon has been discovered in the course of the experimental research of a liquid cooled gas turbine. A similar unstable behavior can be observed in some types of centrifuges and a malfunctioning jet engine with trapped oil in the rotor. In such rotor systems asynchronous whirls are in general induced by wave motions in the liquid which travel backward relative to the rotor.
In the present work the stability of a hollow cylindrical rotor with liquid in it supported by an overhung shaft is investigated. Assuming rotor vibrations to be small, liquid inviscid, and external damping negligible, perturbed motion of the liquid-rotor system are analyzed. The stability of the system is predicted by examining if the solutions of the characteristic equation contains a pair of complex conjugates, or not. The stability of the system is predicted by examining if the solutions of the frequency equation contain a pair of complex conjugates.
The results show that the three-dimensional waves in essence induces the conical mode instability of the rotor while the two-dimensional wave causes the parallel mode whirl. Therefore, if the normal mode of the rotor vibration is coupled type, the rotor can be destabilized by both kinds of liquid waves. In general the asynchronous whirl can be induced in the regions where the rotor speed is nearly equal to the sum of the natural frequency of whirl of the empty rotor and one of the natural frequencies of the liquid waves. The dependence of stability on the gyroscopic effect is also examined. The theory has been verified by the experiments.