Closure to “Discussion of ‘Air-Hammer Instability in Pressurized-Journal Gas Bearings’” (1961, ASME J. Basic Eng., 83, p. 242)

Lazar Licht

doi:10.1115/1.3658934

On the Dynamic Stability of the Spiral-Grooved Gas-Lubricated Thrust Bearing

Journal of Tribology ◽

10.1115/1.3261316 ◽

1987 ◽

Vol 109 (1) ◽

pp. 183-188 ◽

Cited By ~ 12

Author(s):

V. N. Constantinescu ◽

S. Galetuse

Keyword(s):

Dynamic Stability ◽

Small Perturbation ◽

Thrust Bearing ◽

Critical Mass ◽

Practical Interest ◽

Unconditionally Stable ◽

Gas Bearings ◽

Air Hammer

The dynamic stability of a blocked center inward pumping spiral grooved thrust bearing is investigated. For this purpose two methods are considered comparatively, namely a standard small perturbation one, and an extension of the method used previously to determine air-hammer phenomena in externally pressurized gas bearings. The first method gives a more detailed description of situations in which the film is stable or unstable, while the second one gives a limit for the speed (or compressibility parameter Λc) up to which the bearing is unconditionally stable. The second method is simpler and of practical interest since at higher speeds the critical mass furnished by the first method is of little practical interest (being too small).

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Discussion: “Air-Hammer Instability in Pressurized-Journal Gas Bearings” (Licht, Lazar, 1961, ASME J. Basic Eng., 83, pp. 235–242)

Journal of Basic Engineering ◽

10.1115/1.3658933 ◽

1961 ◽

Vol 83 (2) ◽

pp. 242-242

Author(s):

D. F. Hays

Keyword(s):

Gas Bearings ◽

Air Hammer

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Rotordynamic Performance of Flexure Pivot Hydrostatic Gas Bearings for Oil-Free Turbomachinery

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.2720518 ◽

2007 ◽

Vol 129 (4) ◽

pp. 1020-1027 ◽

Cited By ~ 27

Author(s):

Xuehua Zhu ◽

Luis San Andrés

Keyword(s):

High Speed ◽

Low Cost ◽

Damping Ratio ◽

Extreme Temperature ◽

Gas Bearings ◽

Speed Increase ◽

Feed Pressure ◽

Motor Test ◽

Direct Stiffness ◽

Commercial Applications

Micro-turbomachinery demands gas bearings to ensure compactness, light weight, and extreme temperature operation. Gas bearings with large stiffness and damping, and preferably of low cost, will enable successful commercial applications. Presently, tests conducted on a small rotor supported on flexure pivot hydrostatic pad gas bearings (FPTPBs) demonstrate stable rotordynamic responses up to 100,000rpm (limit of the drive motor). Test rotor responses show the feed pressure raises the system critical speed (increase in bearing direct stiffness) while the viscous damping ratio decreases. Predictions correlate favorably with experimentally identified (synchronous) direct stiffness bearing force coefficients. Identified experimental gas bearing synchronous damping coefficients are 50% or less of the predicted magnitudes, though remaining relatively constant as the rotor speed increases. Tests without feed pressure show the rotor becomes unstable at ∼81krpm with a whirl frequency ratio of 20%. FPTPBs are mechanically complex and more expensive than cylindrical plain bearings. However, their enhanced stability characteristics and predictable rotordynamic performance makes them desirable for the envisioned oil-free applications in high speed micro-turbomachinery.

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Externally pressurized gas bearings in a mixed configuration

Proceedings of the Institution of Mechanical Engineers Part K Journal of Multi-body Dynamics ◽

10.1243/14644190260070411 ◽

2002 ◽

Vol 216 (2) ◽

pp. 181-189

Author(s):

A Cazan ◽

R Gohar ◽

M M A Safa

Keyword(s):

Full Length ◽

The Other ◽

Gas Bearings ◽

High Stiffness ◽

Parallel Arrangement ◽

Gas Bearing

This paper analyses the stabilityof an externally pressurized gas bearing (EPB) in a series-parallel arrangement. This mixed con. guration is an alternative to the rigidly mounted single bearing with no external damping, yielding, as one extreme, a high stiffness, but a low whirl threshold speed. The other extreme is a series bearing arrangement with a full-length externally pressurized sleeve between the journal and the housing, yielding a lower stiffness but a higher whirl threshold speed. The paper shows that a mixed con. guration allows for an increase in whirl threshold speed above that for an equivalent rigidly mounted single bearing but below that for a series arrangement. However, the mixed con. guration is stiffer than the series arrangement.

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Spindle assembly with adjustable output characteristics

10.36652/0042-4633-2021-6-21-23 ◽

2021 ◽

pp. 21-23

Author(s):

Keyword(s):

Spindle Assembly ◽

Performance Characteristics ◽

Taper Angle ◽

Gas Bearings ◽

Output Characteristics ◽

Experimental Bench ◽

Spindle Assemblies

A method for controlling the output characteristics of spindle assemblies based on the use of tapered gas bearings with a small taper angle is proposed. An experimental bench for studying the performance characteristics of these bearings is described. The results of researches of gas-static bearings with a small taper angle are presented. Keywords: spindle assembly, gas-static support, small taper angle, experiment. [email protected]

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On the dynamic stability of high-speed gas bearings: stability study and experimental validation

International Journal Sustainable Construction & Design ◽

10.21825/scad.v2i2.20531 ◽

2011 ◽

Vol 2 (2) ◽

pp. 342-351

Author(s):

T. Waumans ◽

J. Peirs ◽

J. Reynaerts ◽

F. Al-Bender

Keyword(s):

Dynamic Stability ◽

Stability Problem ◽

High Speed ◽

Experimental Validation ◽

Stability Study ◽

Gas Bearings ◽

Aerostatic Bearings ◽

Bearing Dynamics ◽

Wide Operating ◽

Operating Temperature Range

For high-speed applications, gas lubricated bearings offer very specific advantages over other,more conventional bearing technologies: a clean and oil-free solution, virtually wear-free operation, lowfrictional losses, wide operating temperature range, etc. However, the principal drawback involved in theapplication of high-speed gas bearings concerns the dynamic stability problem. Successful applicationtherefore requires control of the rotor-bearing dynamics so as to avoid instabilities.After a detailed study of the dynamic stability problem and the formulation of a convenient stability criterium,a brief overview is given of the currently existing bearing types and configurations for improving the stability.In addition, three strategies are introduced: (i) optimal design of plain aerostatic bearings; (ii) modification ofthe bearing geometry to counteract the destabilising effects in the gas film; and (iii) introduction of dampingexternal to the gas film as to compensate for the destabilising effects.These strategies are worked out into detail leading to the formulation of a series of design rules. Theireffectiveness is validated experimentally at a miniature scale. In recent experiments a rotational speed of1.2 million rpm has been achieved with a 6 mm rotor on aerodynamic journal bearings, leading to a recordDN-number of 7.2 million.

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