Dynamic Performance Characteristics of Floating Ring Bearings With Varied Oil Injection Swirl Control Angles

Abstract

Hydrodynamic instability is a prime causative of performance irregularities and violent vibrations in floatingring bearing (FRB) supported turbosystems. The quest for energyefficient solutions to this has stimulated the development of diverse FRB designgeometries, dimensional relationships, and surfacecontours. Unfortunately, these modifications are characterized mainly by modelpredictors, which results lack sufficient testdata to benchmark their authenticities. This work presents the concept and the testdata of flow redirection in FRBs by using an oilinjection swirlcontrol mechanism (OISCM) to attenuate rotordynamic instabilities. FRBs with radius ratio = 1.75 and clearance ratio = 1.5 are tested for various OISCM angles (0 deg, 30 deg, and 60 deg) and under a specific load = 50 kN/m2. The test results indicate that FRBs with OISCM demonstrate substantial improvements in damping and stability characteristics. Their whirlfrequencyratio (WFR) and crosscoupled forces are lower because of improved symmetry of films' pressureforces (Kxx ≈ Kyy). Although the magnitudes of direct damping are higher (|Cxx| = 16.92 kN s/m for 60 deg and 6.03 kN s/m for 0 deg), the load capacity (Kxx) is slightly lower than the normal (0 deg), injection. Nonetheless, this discrepancy in load capacities becomes insignificant for speeds above 22 krpm. The WFR and subsynchronous amplitudes, which are graphic reflections of the bearingbased instability, become progressively smaller with increasing OISCM angle. However, this advantage at elevated speeds can only be sustained by a corresponding increase in oilsupply pressure to circumvent the advent of a starved innerfilm and its attendant imbalance response and thermal growth. In closure, the OISCM bearing is more effective for mitigating rotordynamic instabilities in turborotors than conventional FRBs.