Shrink fit effects on rotordynamic stability: experimental and theoretical study

摘要

This dissertation presents an experimental and theoretical study of subsynchronousrotordynamic instability in rotors caused by interference and shrink fitinterfaces. The experimental studies show the presence of strong unstable subsynchronousvibrations in two different rotor setups with interference and shrink fitinterfaces that were operated above their first critical speeds. The unstable vibrationsoccur at the first natural frequency of the rotor-bearing system. The instability causedcomplete wreckage of the test rig in one of the setups showing that these vibrations arepotentially dangerous to the safe operation of rotating machines. The two different rotorsetups that are studied are a single-disk rotor mounted on a uniform diameter shaft and atwo-disk rotor with an aluminum sleeve shrink fitted to it at the outer surface of the twodisks. In the single-disk rotor, an adjustable interference arrangement between the diskand the shaft is obtained through a tapered sleeve arrangement, which acts as theinterference fit joint. The unstable sub-synchronous vibrations originate from slippagein the shrink fit and the interference fit interfaces that develop friction forces, which actas destabilizing cross-coupled moments when the rotor is operated above its first criticalspeed. The unique contribution offered through this work is the experimental validationof a physically correct model of internal friction which models the destabilizing mechanism as a system of cross-coupled internal moments at the shrink fit interface. Thedissertation describes stability simulations of various test rotor setups using the correctinternal moments model. A commercial finite-element based software called XLTRCTMis used to perform rotordynamic simulations for stability studies. The method of stabilitystudy is the computation of eigenvalues of the rotor-bearing system. A negative real partof the eigenvalue indicates instability. The simulations include the test rotors that wereexperimentally observed as stable and unstable with shrink and interference fit interfacesin their assemblies. The dissertation also describes the simulations of various imaginedrotor configurations with shrink fit interfaces, and seeks to explain how configurationsdiffer on rotordynamic stability depending upon several rotor-bearing parameters such asgeometry and elastic properties, as well as upon the amount of internal frictionparameters, which differ from configuration to configuration.