Rotating machinery relies on tilting-pad journal bearings (TPJB) to provide static-load support with minimal power-losses, safe pad temperatures and rotor-dynamically stable operation. End users focus on reducing oil flow rate into a bearing to lower costs and to increase power efficiency. This paper presents measurements of the steady-state and dynamic forced performance of a TPJB with focus on the influence of supplied oil flow rate, at 50% and 150% of nominal condition. The test bearing has five pads, L/D = 0.4, spherical pivots with 50% offset and (Cr/R) ≈0.001. The test conditions include operation at various shaft surface speeds (32 m/s-85 m/s) and specific loads (0.17 MPa to 2.1 MPa). Measurements obtained at a steady thermal equilibrium include the journal eccentricity and attitude angle, the oil exit-temperature rise, and the pads’ subsurface temperatures at various locations, circumferential and axial. The rig also includes measurement of the drive torque and shaft speed to produce the bearing drag power loss. Dynamic force coefficients include stiffness, damping, and virtual-mass coefficients. In conclusion, a 50% reduced oil flow rate causes a slight degradation in the bearing static and dynamic force performance and does not make the bearing operation unsafe for tests up to 74 m/s. As an important corollary, the measured bearing drag power differs from the conventional estimate derived from the product of the supplied flow rate, the lubricant specific heat and the oil exit temperature rise.

A numerical model developed by Thorat & Childs [1] has indicated that the conventional frequency independent model for labyrinth seals is invalid for rotor surface velocities reaching a significant fraction of Mach 1. A theoretical one-control-volume (1CV) model based on a leakage equation that yields a reasonably good comparison with experimental results is considered in the present analysis. The numerical model yields frequency-dependent rotordynamic coefficients for the seal. Three real centrifugal compressors are analyzed to compare stability predictions with and without frequency-dependent labyrinth seal model. Three different compressor services are selected to have a comprehensive scenario in terms of pressure and molecular weight (MW). The molecular weight is very important for Mach number calculation and consequently for the frequency dependent nature of the coefficients. A hydrogen recycle application with MW around 8, a natural gas application with MW around 18, and finally a propane application with molecular weight around 44 are selected for this comparison. Useful indications on the applicability range of frequency dependent coefficients are given.

To validate a new squeeze film damper (SFD) bearing design introduced in [1], a pair of 3.5 inch SFD bearings were manufactured and tested. Static spring compression test was conducted to prove the spring design stiffness calculated through the geometry parametric spring model. High cycle loading fatigue testing of the spring was conducted to validate the design spring fatigue limit. The entire SFD bearing assembly was inspected and checked through a SFD centering bench test before the rotor dynamic test. Unbalance response correlation and logarithmic decrement (Log. Dec.) measurement using the operational modal analysis (OMA) method were employed for the rotor-dynamic tests. An agreement was seen between the analysis and the experimental measurement. It was seen that the SFD bearing provided the extra damping as expected to suppress the unbalance vibration when passing through the critical speed and also improve the stability (Log. Dec.) of the rotor. It was found that the measured SFD damping was closer to the full film damping model when the squeeze oil film was sealed with O-rings. The SFD improved the logarithmic decrement of the rotor-bearing system from 0.07 to more than 0.21 as compared to the system without SFD.

The predicted and measured bearing metal temperatures of tilting-pad journal bearings are examined. All bearings are a five-pad design with load-between-pad orientation. The two loaded pads in each bearing are instrumented with a resistance temperature detector (RTD). The bearing pad metal temperatures are measured as a part of the ISO 10439 (API 617) mechanical test requirement. Bearing pad metal temperatures are predicted using the thermoelastohydrodynamic (TEHD) analysis method. One particular bearing size 4 in. (101.6 mm) in diameter and 1.54 in. (39.12 mm) in the axial length is examined with respect to the tolerance range influence on the predicted pad metal temperatures including the effect of bearing assembled clearance and preloads. A range of loads and speeds are investigated. The temperature variation observed for this bearing size is compared against the variation in the measured temperature data for three other bearing sizes (bearing sizes are denoted by diameter × axial length) 2.95 in. (74.9 mm) × 1.02 in. (25.9 mm), 6 in. (152.4 mm) × 3 in. (76.2 mm), and 8 in. (203.2 mm) × 7 in. (177.8 mm).

The experimental setup for a hole-pattern seal is modeled using computational fluid dynamics (CFD) and results compared with measured test data and bulk flow model (ISOTSEAL) predictions. The inlet swirl boundary condition for prior CFD analyses of this test case have either been assumed or based on pitot-tube measurements. In this paper, the validity of each is investigated by including radial inlet nozzles with the inlet plenum in the model geometry. A transient mesh deformation technique with multiple frequency journal excitations is used to determine frequency-dependent rotordynamic coefficients. This multifrequency excitation method is validated against single frequency sinusoidal journal excitation. An empirical limit on the number of frequencies that can be packed in a multifrequency excitation signal to provide a reasonable estimate of rotordynamic coefficients is provided. Rotordynamic coefficients estimated using CFD compare well with measured rotordynamic coefficients. For the given test data, the ISOTSEAL bulk flow model does not provide good correlation for cross-coupled stiffness if the measured swirl ratio at the inlet of the seal is used in the prediction. However, improvement in correlation for cross-coupled stiffness is obtained if the swirl ratio found from CFD analysis is used in the bulk flow model, indicating that pitot-tube measurements of swirl may not be accurate.