Rotordynamic Analysis of Rotor-Stator Rub Using Rough Surface Contact

Undesirable rotor-stator rub is frequently observed in rotordynamic systems, and has been the subject of many investigations. Most of these studies employ a simple piecewise-smooth linear-elastic contact model (LECM), where the rotor switches between noncontacting and contacting operation once the clearance is exceeded (various complications have been incorporated, though the essential model premises endure). Though useful as a first step, the LECM relies on an arcane contact stiffness estimate, and therefore does not emulate the actual contacting surfaces. Consequentially, the LECM fails to elucidate how real surface parameters influence contact severity and surface durability. This work develops a novel model for rotor-stator rub which is commensurate with reality by treating the surfaces as a collection of stochastically distributed asperities. Specifically, the elastoplastic Jackson-Green (JG) rough surface contact model is used to calculate the quasistatic contact force as a function of rotor displacement, where bulk material deformation and surface cumulative damage are ignored. A simple exponential fit of the contact force is proposed to reduce computational burden associated with evaluating the JG rough surface contact model at each simulation time step. The rotor's response using the LECM and JG rough surface contact model is compared via shaft speed bifurcations and orbit analysis. Significant differences are observed between the models, though some similarities exist for responses with few contacts per rotor revolution.