Journal Bearing Vibration and SSV Hash

DeCamillo, Scan M.; He, Minhui; Cloud, C. Hunter

doi:10.21423/r1dh1j

Cited by 8 publications

(3 citation statements)

References 2 publications

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“…Reporting in full the experimental results for the flooded bearing, Refs. [8,9] describe the appearance of subsynchronous shaft vibrations (SSV) [1] for operating conditions under a low specific load (345 kPa at 6 krpm) and with the bearing supplied with low magnitudes flow rates, 15%  2% of nominal. The found SSV "hash" has a broad band frequency spectrum well below the synchronous frequency and lacking discrete frequency peaks; however the amplitude of the SSV is rather small compared to the bearing synchronous motion amplitude.…”

Section: Subsynchronous Whirl Motions In Bearing Supplied With a Low ...mentioning

confidence: 99%

“…A reduced flow decreases pumping costs and oil sump storage, and improves system energy efficiency. Note that operation with a too low flow rate in evacuated TPJBs, nearly unloaded, can produce the infamous subsynchronous shaft vibrations (SSV hash) [1]. A too low flow rate may also produce a quick raise in pad temperature that could degrade and even melt the Babbitt layer [2].…”

Section: Introductionmentioning

confidence: 99%

“…During the last two decades, the Turbomachinery Symposium published several relevant lectures that showcase the effect of reduced flow rate on bearing performance. Distinctive contributions are those of DeCamillo et al [10,1], Nicholas et al [11], and Whalen et al [12]. References [6][7][8][9] present critical reviews of the past literature, including modeling approaches and comparisons to experimental data.…”

Section: Introductionmentioning

confidence: 99%

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Effect of a Reduced Oil Flow Rate on the Static and Dynamic Performance of a Tilting Pad Journal Bearing Running in Both the Flooded and Evacuated Conditions

Andrés

Alcantar

2023

Journal of Engineering for Gas Turbines and Power

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The efficiency of rotating machinery improves as drag power losses in bearings reduce; hence, an operation mode that reduces the supplied flow brings immediate benefits. The paper presents measurements of the static and dynamic load performance of a flooded and evacuated tilting pad journal bearing supplied with flow rates from 150% to ~25% (or lesser) of a nominal magnitude. The four pads bearing has center pivots with single orifice feeds for the flooded condition and spray bar injection for the evacuated condition. The shaft, 102 mm in diameter, operates at 6 and 12 krpm while a static load is applied between pads (LBP). The specific loads equal 345, 1,034 and 2,068 kPa. Pad subsurface temperatures show the evacuated bearing is colder by a few degrees Celsius. Drag power losses in the evacuated bearing produce up to ~40% lesser power loss for a nominal oil flow rate. The bearings direct stiffnesses increase with applied load and show little dependency on shaft speed. The evacuated bearing has lower magnitude stiffnesses (20% or so lesser). Direct damping coefficients reduce in magnitude as the flowrate decreases, in particular for the evacuated bearing. For sufficiently small flow rates, operation at low speeds and low loads produced subsynchronous shaft vibrations with a broad band spectrum (SSV hash). The experimental campaign demonstrates that tilting pad bearings (flooded and evacuated) can safely operate with a reduced flow rate to produce significant savings in drag power losses and without significant effect on the pads' metal temperatures.

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Section: Subsynchronous Whirl Motions In Bearing Supplied With a Low ...mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Effect of a Reduced Oil Flow Rate on the Static and Dynamic Performance of a Tilting Pad Journal Bearing Running in Both the Flooded and Evacuated Conditions

Andrés

Alcantar

2023

Journal of Engineering for Gas Turbines and Power

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Effect of Flow Rate on the Performance of an Evacuated Tilting Pad Journal Bearing: Load on Pad vs. Load-Between-Pad Configurations

San Andrés,

Alcantar

2023

Mechanisms and Machine Science

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A Flow Starvation Model for Tilting Pad Journal Bearings and Evaluation of Frequency Response Functions: A Contribution Towards Understanding the Onset of Low Frequency Shaft Motions

Andrés

Koo

Hemmi

2017

Volume 7A: Structures and Dynamics

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Direct lubrication tilting pad journal bearings (TPJBs) require of less oil flow, reduce power consumption and offer cooler pad temperatures for operation at high surface speeds. Although apparently free of a hydrodynamic instability, the literature shows that direct lubrication TPJBs exhibit unexpected shaft vibrations with a broadband low frequency range, albeit small in amplitude. Published industrial practice demonstrates the inlet lubrication type, a reduced supply flow rate causing film starvation, and the bearing discharge conditions (evacuated or end sealed) affect the onset, gravity and persistency of the sub synchronous (SSV) hash motions. The paper presents a physical model to predict the performance of TPJBs with flow conditions ranging from over flooded to extreme starvation. Lubricant starvation occurs first on an unloaded pad, thus producing a (beneficial) reduction in drag power. As the supplied flowrate decreases further, fluid starvation moves towards the loaded pads and affects the film temperature and power loss, increases the journal eccentricity, and modifies the dynamic force coefficients of each tilting pad and thus the whole bearing. For a point mass rotor supported on a TPJB, the analysis produces eigenvalues and frequency response functions (FRFs) from three physical models for lateral rotor displacements: one with frequency reduced (4×4) bearing stiffness (K) and damping (C) coefficients and another with constant K-C-M (inertia) coefficients over a frequency range. The third model keeps the degrees of freedom (tilting) of each pad and incorporates the full matrices of force coefficients including fluid inertia. Predictions of rotordynamic performance follow for two TPJBs: one bearing with load between pads (LBP) configuration, and the other with a load on a pad (LOP) configuration. For both examples, under increasingly poor lubricant flow conditions, the damping ratio for the rotor-bearing low frequency (SSV) modes decreases, thus producing an increase in the amplitude of the FRFs. For the LOP bearing, a large static load produces a significant asymmetry in the force coefficients; the rotor-bearing has a small stiffness and damping for shaft displacements in the direction orthogonal to the load. A reduction in lubricant flow only exacerbates the phenomenon; starvation reaches the loaded pad to eventually cause the onset of low frequency (SSV) instability. The bearing analyzed showed similar behavior in a test bench. The predictions thus show a direct correlation between lubricant flow starvation and the onset of SSV.

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Journal Bearing Vibration and SSV Hash

Cited by 8 publications

References 2 publications

Effect of a Reduced Oil Flow Rate on the Static and Dynamic Performance of a Tilting Pad Journal Bearing Running in Both the Flooded and Evacuated Conditions

Effect of a Reduced Oil Flow Rate on the Static and Dynamic Performance of a Tilting Pad Journal Bearing Running in Both the Flooded and Evacuated Conditions

Effect of Flow Rate on the Performance of an Evacuated Tilting Pad Journal Bearing: Load on Pad vs. Load-Between-Pad Configurations

A Flow Starvation Model for Tilting Pad Journal Bearings and Evaluation of Frequency Response Functions: A Contribution Towards Understanding the Onset of Low Frequency Shaft Motions

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