A Review of the State-of-the-Art for the Design of Self-Acting Gas-Lubricated Bearings

Fuller, D. D.

doi:10.1115/1.3554857

Cited by 42 publications

(15 citation statements)

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“…Natural vibrations of such frequencies that are observed under these circumstances are self-excited vibrations. In literature this phenomenon is called`air hammer' (24). Figure 6 presents a more exact analysis of the air hammer phenomenon.…”

Section: Air Hammermentioning

confidence: 99%

Stiffness and damping coefficients of air rings with a chamber feeding system

Czołczyński

Kapitaniak

Marynowski

1998

Proceedings of the Institution of Mechanical Engineers, Part J:

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When, during the operation of rotors supported in gas bearings, their rotational velocity reaches a sufficiently high value, loss of steady state stability occurs. This instability is caused by the loss of damping properties of the gas film, which leads to self-excited vibrations. These vibrations are the basic obstacle to a widespread application of gas bearings. The phenomenon of self-excited vibrations can be avoided by introducing an elastic supporting structure between the bearing bushes and the casing, characterized by properly selected stiffness and damping coefficients. In practice, such a structure can have the form of an externally pressurized gas ring.In this paper, on the basis of selected examples, those ranges of the values of stiffness and damping coefficients of the gas ring that make it possible to retain steady state stability at practically any rotational velocity of the rotor are demonstrated. A design of the ring structure, especially of its feeding system, is also shown, which ensures the required values of stiffness and damping coefficients (with regard to the stability). These investigations have been carried out by means of a numerical simulation method with the use of a mathematical model of the gas bearing, which has already been verified many times.

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Section: Air Hammermentioning

confidence: 99%

Stiffness and damping coefficients of air rings with a chamber feeding system

Czołczyński

Kapitaniak

Marynowski

1998

Proceedings of the Institution of Mechanical Engineers, Part J:

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“…Bearing load decreases with shaft power; thus facilitating the use of bearing technologies with limited load capacity such as gas-lubricated bearings. An early and remarkable investigation of different self-acting gas bearing configurations is given by Fuller [6]. Hence, providing gas-lubricated bearing technology with reduced windage losses not only yields beneficial effect on overall efficiency but also facilitates the implementation of small-scale turbomachinery with regards to thermal management.…”

Section: Introductionmentioning

confidence: 99%

Enhanced Groove Geometry for Herringbone Grooved Journal Bearings

Schiffmann

2013

Journal of Engineering for Gas Turbines and Power

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Although gas-lubricated herringbone grooved journal bearings (HGJB) are known for high rotordynamic stability thresholds, small clearance to diameter ratios are required for stable rotor operation. Tight clearances not only increase bearing losses but also yield challenging manufacturing and assembly tolerances, which ultimately translate into cost. Traditionally, the grooves of HGJB are of helical nature with constant cross section and pitch. The current paper aims at increasing the clearance to diameter ratio and the stability threshold of grooved bearings by introducing enhanced groove geometries. The axial evolution of groove width, depth, and local pitch are described by individual third order polynomials with four interpolation points. The expression for the smooth pressure distribution resulting from the narrow groove theory is modified to enable the calculation of bearing properties with modified groove patterns. The reduced order bearing model is coupled to a linear rigid body rotordynamic model for predicting the whirl speed map and the corresponding stability. By introducing a critical mass parameter as a measure for stability, a criterion for the instability onset is proposed. The optimum groove geometry is found by coupling the gas bearing supported rotor model with a multiobjective optimizer. By maximizing both the clearance to diameter ratio and the rotordynamic stability it is shown that with optimal groove geometry, which deviates from helicoids with constant pitch and cross section, the critical mass parameter can be improved by more than one order of magnitude compared to traditional HGJB geometries. The clearance to diameter ratio can be increased by up to 80% while keeping the same stability margin, thus reducing both losses and manufacturing constraints. The optimum groove pattern distributions (width ratio, angle, and depth) are summarized for a variety of LID ratios and for different compressibility numbers in a first attempt to set up general design guidelines for enhanced gas-lubricated HGJB.Nature of the Issues. Gas bearing technology falls into two categories: externally pressurized or dynamic. In the latter case the relative shear motion between rotor and sleeve combined with Journal of Engineering for Gas Turbines and Power

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“…Micro-turbomachinery demands gas bearings to ensure compactness, lightweight and extreme temperature operation [1,2]. Gas film bearings, unlike oil-lubricated bearings, offer advantages of low friction and less heat generation.…”

Section: Introductionmentioning

confidence: 99%

“…Estimation of the gas bearing equivalent stiffnessThe gas bearing equivalent stiffness K eq can be obtained from the system critical speed (ω c ) and the rotor mass shared by each bearing (M 1 =0.435 kg), i.e. K eq = M 1 ω c2 .…”

mentioning

confidence: 99%

Experimental Response of a Rotor Supported on Rayleigh Step Gas Bearings

Zhu¹,

́s

2005

Volume 4: Turbo Expo 2005

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Reliable gas bearings will enable the rapid deployment of high speed oil-free micro-turbomachinery. This paper presents analysis and experiments of the dynamic performance of a small rotor supported on Rayleigh step gas bearings. Comprehensive tests demonstrate that Rayleigh step hybrid gas bearings exhibit adequate stiffness and damping capability in a narrow range of shaft speeds, up to ∼ 20 krpm. Rotor coast down responses were performed with two test bearing sets with nominal radial clearance of 25 μm and 38 μm. A near-frictionless carbon (NFC) coating was applied on the rotor to reduce friction at liftoff and touchdown. However, the rotor could not lift easily and severe rubbing occurred at shaft speeds below ∼ 4,000 rpm. The tests show that the supply pressure raises the rotor critical speed and decreases the system damping ratio, while only affecting slightly the rotor-bearing system onset speed of instability. Whirl frequencies are nearly fixed at the system natural frequency (∼ 120 Hz) with subsynchronous amplitude motions of very large magnitude that prevented rotor operation above ∼ 20 krpm. The geometry of the Rayleigh steps distributed on the rotor surface generates a time varying pressure field, resulting in a sizable 4X super synchronous component of bearing transmitted load. Predictions show the synchronous stiffness and damping coefficients decrease with shaft speed. Predicted threshold speeds of instability are much lower than measured values due to the analytical model limitations assuming a grooved stator. The predicted synchronous responses to imbalance correlate well with the measurements. The Rayleigh step gas bearings are the most unreliable rigid bearing configuration tested to date.

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A Review of the State-of-the-Art for the Design of Self-Acting Gas-Lubricated Bearings

Cited by 42 publications

References 0 publications

Stiffness and damping coefficients of air rings with a chamber feeding system

Stiffness and damping coefficients of air rings with a chamber feeding system

Enhanced Groove Geometry for Herringbone Grooved Journal Bearings

Experimental Response of a Rotor Supported on Rayleigh Step Gas Bearings

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