Stability Performance Comparison of Rotor-Bearing Systems Supported on Conventional and Hybrid Journal Bearings

摘要

New closed form expressions for calculating the linear stability thresholds for rigid and flexible Jeffcott systems as well as the imbalance response for a rotor supported on a hybrid bearing are presented. Comparing stability values using the expression here developed to that obtained by Lund, the thresholds are practically the same. The presented hybrid bearing design has a single injection port whose location is so chosen that it helps stabilize the bearing performance; likewise, the resultant equilibrium attitude angle is reduced. Rotordynamic coefficients graphs for conventional and the pressurized bearing as of Sommerfeld number are presented. Feeding such rotordynamic coefficients into the expressions for both, the corresponding velocity thresholds and the imbalance response, the system stability and vibration performances are estimated and analyzed. When comparing the Jeffcott conventional journal bearings to that of this hybrid type, results show a clear superiority of the injected design as far as stability behavior is concerned. Specifically, for flexible industrial shafts our analysis shows that usage of this design yields a velocity threshold between 25% to 40% higher than the conventional circular ones. Moreover, this hybrid bearing is capable of reducing the synchronous vibration amplitude in most speed ranges, except around the critical speed; for certain Jeffcott configurations the amplitude reduction can be substantial.