Breathing Crack Model Effect on Rotor's Postresonance Backward Whirl

Abstract

In this work, we investigate the appearance of postresonance backward whirl (Po-BW) using the model of a rotor with a breathing crack. This phenomenon could be employed as an indicator of crack and bearing damage in rotor systems that undergo recurrent passage through critical forward whirl rotational speed during startup and coast down operations. The finite element (FE) model is used to develop the linear-time-varying equations of motion of the considered accelerating cracked rotor. The whirl response is obtained by direct numerical integration. In addition, the effect of bearing anisotropy on Po-BW excitation is investigated. It is found that the appearance of Po-BW zones is significantly affected by the depth of the crack, angular acceleration rate, anisotropy of bearings, and the orientation of the unbalance force vector with respect to the crack opening direction. The full spectrum analysis (FSA) is also employed and found to be an efficient tool for identifying the Po-BW zones of rotational speeds in the whirl response.