Aligned and Misaligned Wear Pattern in Fluid Film Bearings and Influence on the Rotor Response

Journal bearings are subjected to wear when rub effect happens during the start up or the operation of the rotating system. The wear pattern in many cases is uniformly extended along the width of the bearing. In some other cases the wear pattern is non-uniformly distributed but misaligned along the width, because the rotating shaft inside the bearing operates in misaligned conditions. In this work a rotor bearing system composed of a multi-step rotor and worn fluid film bearings is simulated, in order to notify the effect of the wear on the dynamic characteristics of the system. The bearing wear pattern is considered as aligned, following the Dufrane’s model, or misaligned, when the rotor is whirling misaligned. In the first part of this investigation, the finite element method (FEM) is used in order to solve the Reynolds equation and then to calculate the bearing dynamic characteristics, as functions of Sommerfeld number, L/D ratio and several combinations of journal and wear pattern misalignment angles. The bearing’s stiffness and damping have been adopted in system’s properties during operation. In the second part, the physical system is simulated by considering continuous shaft theory, including hysteretic damping and using the nonlinear bearing stiffness and damping coefficients calculated in the first part. Thus the dynamic response can be calculated. Comparison of the response for aligned and misaligned wear pattern is also included. Notifications for critical speed shift, system anisotropy and additional harmonics in the response spectra are made during system’s virtual start up.