An analytic study of the packing rub effect in rotating machinery

Abstract

The packing rub effect is the vibration produced when an eccentric rotor rubs on a stationary component, the rub caused by a thermal bow resulting from a non-uniform distribution of the rubbing heat. Burt Neukirk, in 1924, first noticed this phenomenon and gave a qualitative explanation for it. Since then, several investigators proposed simplified models to describe the Packing Rub Effect. The Effect is not yet well enough understood. This and the increasing importance of it in designing high speed turbine rotors demand further work in this area. In this work, an analytic study of the phenomenon is undertaken. A transient, three dimensional heat transfer model in an infite, hollow cylinder is used to describe the temperature fie1d. The temperature is integrated according the Goodier's formu1a for the average flexural rotation; this gives the geometric bow. Finally the known complex polar receptance of the systsm at the rubbing position and the dependence of the heat generation on the dynamic amplitude are used in order to establish an analytic model of the system. It can be described by two nonlinear ordinary differential equations. The solution of these equations correlate very well with test data. It was found that the main parameter that aftects the rubbing stability is the phase angle between geometric and dynamic bow. New modes of the packing rub etfect were discovered analytically and verified experimentally. It is believed that this analysis will contribute to the better understanding o£ the packing rub effect and that it will be applied for design of high speed rotating machinery with higher efficiency and better reliability.