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Research Papers

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

[+] Author and Article Information
Daniel Tamunodukobipi

Korea University of Science and Technology,
Yuseong-gu, Deajeon, South Korea
e-mail: tamunodan@yahoo.com

Chang Ho Kim

Center of Urban Energy System Research,
Korea Institute of Science and Technology,
Songbuk-gu, Seoul, South Korea
e-mail: kimch@kist.re.kr

Yong-Bok Lee

Center of Urban Energy System Research,
Korea Institute of Science and Technology,
Songbuk-gu, Seoul, South Korea
e-mail: lyb@kist.re.kr

1Corresponding author.

Contributed by the Dynamic Systems Division of ASME for publication in the JOURNAL OF DYNAMIC SYSTEMS, MEASUREMENT, AND CONTROL. Manuscript received November 8, 2013; final manuscript received June 9, 2014; published online September 10, 2014. Assoc. Editor: Jiong Tang.

J. Dyn. Sys., Meas., Control 137(2), 021002 (Sep 10, 2014) (11 pages) Paper No: DS-13-1440; doi: 10.1115/1.4027912 History: Received November 08, 2013; Revised June 09, 2014

Hydrodynamic instability is a prime causative of performance irregularities and violent vibrations in floating-ring bearing (FRB) supported turbosystems. The quest for energy-efficient solutions to this has stimulated the development of diverse FRB design-geometries, dimensional relationships, and surface-contours. Unfortunately, these modifications are characterized mainly by model-predictors, which results lack sufficient test-data to benchmark their authenticities. This work presents the concept and the test-data of flow redirection in FRBs by using an oil-injection swirl-control 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 whirl-frequency-ratio (WFR) and cross-coupled forces are lower because of improved symmetry of films' pressure-forces (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 bearing-based instability, become progressively smaller with increasing OISCM angle. However, this advantage at elevated speeds can only be sustained by a corresponding increase in oil-supply pressure to circumvent the advent of a starved inner-film 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.

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Figures

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Fig. 1

Representation of the two-parallel-film bearing geometry and flow pattern

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Fig. 2

FRB signal waterfall for speed-up-and-down test showing the regions of low and high peaks

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Fig. 3

Schematic of FRB OISCM defining the oil-injection angle (Φ)

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Fig. 4

Representations of FRB sensors mounting and the two-film force configuration

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Fig. 5

Consequences of improper frequency span selection

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Fig. 6

Curve-fittings of FRB impedance and response functions for a well-chosen frequency span (Φ = 0 deg at ΩJ = 10 krpm)

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Fig. 7

Comparison of curve-fitting and raw data of FRB response functions for 60 deg-injection at ΩJ = 10 krpm

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Fig. 8

Descriptive section view of FRB rotordynamic test-rig

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Fig. 9

Depiction of structural rotor and predicted free-free mode shapes, Ref. [15]

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Fig. 10

FRB self-excited signal waterfall for normal injection at ΩJ = 12 krpm

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Fig. 11

Plots of the frequencies of signal peaks versus the journal speed

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Fig. 12

FRB stiffness coefficients for Φ = 0 deg, 60 deg

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Fig. 13

FRB damping coefficients for Φ = 0 deg, 60 deg

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Fig. 14

FRB inertia coefficients for Φ = 0 deg, 60 deg

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Fig. 15

Impact of different OISCM angles on FRB rotordynamic behavior

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Fig. 16

Impact of varied OISCM angles on FRB WFR

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