Some Experiments on Oil Whirl and Oil Whip

A. El-Shafei; S. H. Tawfick; M. S. Raafat; G. M. Aziz

doi:10.1115/1.2181185

Some Experiments on Oil Whirl and Oil Whip

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.2181185 ◽

2004 ◽

Vol 129 (1) ◽

pp. 144-153 ◽

Cited By ~ 25

Author(s):

A. El-Shafei ◽

S. H. Tawfick ◽

M. S. Raafat ◽

G. M. Aziz

Keyword(s):

Twentieth Century ◽

Critical Speed ◽

Journal Bearings ◽

Flexible Rotor ◽

Angular Misalignment ◽

Oil Whip ◽

Early Twentieth Century ◽

Oil Whirl

The oil whirl and oil whip phenomena have been well known since the early twentieth century. However, there is a lot of confusion on the parameters that affect the onset of instability. In this study, we investigate the onset of instability on a flexible rotor mounted on two plain cylindrical journal bearings. The rotor is run through the first critical speed, the instability, and the second critical speed. Tests are conducted at various unbalance levels, pressures, and misalignment conditions on the coupling. It is shown that, by far, the misalignment of the coupling is the parameter that is most effective on the onset of instability. In particular angular misalignment resulted in the smoothest rotor response.

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Some Experiments on Oil Whirl and Oil Whip

Volume 6: Turbo Expo 2004 ◽

10.1115/gt2004-53644 ◽

2004 ◽

Author(s):

A. El-Shafei ◽

S. H. Tawfick ◽

M. S. Raafat ◽

G. M. Aziz

Keyword(s):

Twentieth Century ◽

Critical Speed ◽

Journal Bearings ◽

Flexible Rotor ◽

Angular Misalignment ◽

Oil Whip ◽

Early Twentieth Century ◽

Oil Whirl

The oil whirl and oil whip phenomena are well known since the early twentieth century. However, there is a lot of confusion on the parameters that affect the onset of instability. In this study, we investigate the onset of instability on a flexible rotor mounted on two plain cylindrical journal bearings. The rotor is run through the first critical speed, the instability, and the second critical speed. Tests are conducted at various unbalance levels, pressures, and misalignment conditions on the coupling. It is shown that, by far, the misalignment of the coupling is the parameter that is most effective on the onset of instability. In particular angular misalignment resulted in the smoothest rotor response.

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Experimental Investigation of the Effect of Angular Misalignment on the Instability of Plain Journal Bearings

ASME/STLE 2009 International Joint Tribology Conference ◽

10.1115/ijtc2009-15057 ◽

2009 ◽

Cited By ~ 1

Author(s):

Aly El-Shafei ◽

Sameh H. Tawfick ◽

Mokhtar O. A. Mokhtar

Keyword(s):

Journal Bearings ◽

Displacement Sensor ◽

Maximum Speed ◽

Test Rig ◽

Angular Misalignment ◽

Vibration Displacement ◽

Oil Whip ◽

Fluid Film Bearings ◽

Oil Whirl ◽

Overall Stability

The effect of angular misalignment of plain journal bearings on the oil whirl and oil whip phenomena was investigated using a test rig comprising a flexible one inch diameter shaft supported on two cylindrical fluid film bearings. A matrix of experiments was designed where a precisely controlled angular misalignment between the shaft and the drive end, the non-drive end, or both bearings was induced. In each case we measure the onset of oil whirl and/or the onset of oil whip and the maximum speed that the test rig can reach before reaching a maximum vibration displacement of 1 mm at the location of the displacement sensor. The results show clearly that the angular misalignment of the bearings with respect to the shaft help delay the onset of oil whip from 3200 rpm to 4500 rpm in some cases. An interesting and new observation was the effect of the configuration of the misalignment on the overall stability characteristics. In particular, when the two bearings were misaligned in the same direction such that the two misaligned bearing planes were parallel to each other the onset of instability was more delayed and the overall operation was smoother.

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Controlling Journal Bearing Instability Using Active Magnetic Bearings

Volume 5: Turbo Expo 2007 ◽

10.1115/gt2007-28059 ◽

2007 ◽

Cited By ~ 5

Author(s):

A. El-Shafei ◽

A. S. Dimitri

Keyword(s):

Journal Bearing ◽

Magnetic Bearing ◽

Journal Bearings ◽

Active Magnetic Bearing ◽

Rotating Speed ◽

Damping Characteristics ◽

Oil Whip ◽

Novel Approach ◽

Oil Whirl ◽

Load Carrying

Journal Bearings are excellent bearings due to their large load carrying capacity and favorable damping characteristics. However, Journal bearings are known to be prone to instabilities. The oil whirl and oil whip instabilities limit the rotor maximum rotating speed. In this paper, a novel approach is used to control the Journal bearing (JB) instability. An Active Magnetic Bearing (AMB) is used to overcome the JB instability and to increase its range of operation. The concept is quite simple: rather than using the AMB as a load carrying element, the AMB is used as a controller only, resulting in a much smaller and more efficient AMB. The load carrying is done by the Journal bearings, exploiting their excellent load carrying capabilities, and the JB instability is overcome with the AMB. This results in a combined AMB/JB that exploits the advantages of each device, and eliminates the deficiencies of each bearing. Different controllers for the AMB to control the JB instability are examined and compared theoretically and numerically. The possibility of collocating the JB and the AMB is also examined. The results illustrate the effectiveness of the concept.

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Blade Loss Simulation of Multi Mass Rotor Model With Nonlinear Tilt Pad Journal Bearings

Volume 5: Manufacturing Materials and Metallurgy; Ceramics; Structures and Dynamics; Controls, Diagnostics and Instrumentation; Education; IGTI Scholar Award ◽

10.1115/95-gt-433 ◽

1995 ◽

Author(s):

R. K. Gadangi ◽

A. B. Palazzolo

Keyword(s):

Natural Frequency ◽

Transient Response ◽

Critical Speed ◽

Journal Bearings ◽

Rigid Rotor ◽

Flexible Rotor ◽

Equilibrium Location ◽

Rotor Model ◽

Limiting Value ◽

Bearing System

Prediction of rotor vibrations due to large imbalance requires nonlinear solution of the supporting bearings. This paper presents a methodology and results for the effects of large, sudden imbalance on the response of a multi mass rotor model supported on tilt pad journal bearings. For a given imbalance, response is obtained for rotor speeds below, above and at the rotor natural frequency. The maximum peak to peak amplitude is larger at the critical speed than at a speed above or below the critical. The imbalance response is compared with two other methods used for predicting the transient response of a rotor bearing system. The rigid rotor and nonlinear bearing model shows a response similar in shape to that obtained with a flexible rotor and nonlinear bearing model, but the magnitude is different, which reached a limiting value as the imbalance was increased. The flexible rotor and linearized bearing model predicts a similar trend as the flexible rotor and nonlinear bearing model, with increasing speed for a given imbalance, but the shape and magnitude of the orbit is completely different. The motion of rotor to static equilibrium location for the flexible rotor and nonlinear bearing model showed oscillations which diminished with time, while the rigid rotor and nonlinear bearing model does not show any oscillations.

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The Stability of an Elastic Rotor in Journal Bearings With Flexible, Damped Supports

Journal of Applied Mechanics ◽

10.1115/1.3627335 ◽

1965 ◽

Vol 32 (4) ◽

pp. 911-920 ◽

Cited By ~ 91

Author(s):

Jorgen W. Lund

Keyword(s):

Theoretical Analysis ◽

Dynamic Properties ◽

Journal Bearings ◽

Rotor Speed ◽

Flexible Rotor ◽

Damping Coefficients ◽

Oil Whip ◽

The Stability ◽

Rotor Stiffness ◽

Gas Bearing

A theoretical analysis is presented investigating the stability (fractional frequency whirl, “oil whip”) of a symmetrical, flexible rotor supported in journal bearings. The bearings are mounted in flexible, damped supports. The analysis determines the rotor speed at which instability sets in as affected by rotor stiffness, the dynamic properties of the bearing film, and the flexibility and damping of the bearing supports. The analysis is based on the fact that the bearing can be represented by frequency-dependent spring and damping coefficients, and the method by which the coefficients are obtained is described with emphasis on the gas-lubricated bearing. The conclusions are: (a) Rotor and support flexibility by themselves lower the speed at onset of instability; (b) when the bearing support possesses damping in addition to flexibility, the speed at onset of instability can be raised significantly above the threshold speed of a rotor in rigidly mounted bearings. Numerical results are presented in the form of graphs for the plain cylindrical gas bearing.

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Active Self-Excited Vibration Elimination of Rotating Machine With an Electromagnetic Exciter

Volume 1: 22nd Biennial Conference on Mechanical Vibration and Noise, Parts A and B ◽

10.1115/detc2009-86405 ◽

2009 ◽

Cited By ~ 1

Author(s):

Chen-Chao Fan ◽

Min-Chun Pan

Keyword(s):

Journal Bearings ◽

Rotor System ◽

Stable Method ◽

Rotating Machine ◽

Oil Whip ◽

Control Scheme ◽

Oil Whirl ◽

Excited Vibration ◽

Load Carrying ◽

Auxiliary Device

Journal bearings are commonly used in large rotary machineries because they have excellent mechanical and geometric properties as well as large load-carrying capacities. Nevertheless, the oil whirl and oil whip instabilities limit their applications due to their insufficient stiffness at high running speeds. This paper presents a method to increase the stiffness of a rotating machine using an electromagnetic exciter (EE), which can raise the threshold of instability of the rotating machine and eliminate fluid-induced instability. The EE is a controllable auxiliary device that can provide additional stiffness to the bearings to increase the operating ranges of a rotating machine, while the journal bearings act as load-carrying devices. Together, the EE complements the JB to stiffen the rotor system and raise the threshold of instability. A simple control scheme is used to calculate the amount of supplemental stiffness supplied by the EE. The experimental results demonstrate that the oil whirl and oil whip instabilities of the rotating machine can be eliminated effectively, even at higher running speeds. The advantage of the EE is to offer a faster, more stable method to eliminate fluid-induced instability.

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Controlling Journal Bearing Instability Using Active Magnetic Bearings

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.3078785 ◽

2009 ◽

Vol 132 (1) ◽

Cited By ~ 31

Author(s):

A. El-Shafei ◽

A. S. Dimitri

Keyword(s):

Journal Bearing ◽

Magnetic Bearing ◽

Journal Bearings ◽

Active Magnetic Bearing ◽

Rotating Speed ◽

Damping Characteristics ◽

Oil Whip ◽

Novel Approach ◽

Oil Whirl ◽

Load Carrying

Journal bearings (JBs) are excellent bearings due to their large load carrying capacity and favorable damping characteristics. However, journal bearings are known to be prone to instabilities. The oil whirl and oil whip instabilities limit the rotor maximum rotating speed. In this paper, a novel approach is used to control the journal bearing instability. An active magnetic bearing (AMB) is used to overcome the JB instability and to increase its range of operation. The concept is quite simple: Rather than using the AMB as a load carrying element, the AMB is used as a controller only, resulting in a much smaller and more efficient AMB. The load carrying is done by the journal bearings, exploiting their excellent load carrying capabilities, and the JB instability is overcome with the AMB. This results in a combined AMB/JB that exploits the advantages of each device and eliminates the deficiencies of each bearing. Different controllers for the AMB to control the JB instability are examined and compared theoretically and numerically. The possibility of collocating the JB and the AMB is also examined. The results illustrate the effectiveness of the concept.

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Some Polish Composers of To-Day

Tempo ◽

10.1017/s0040298200053596 ◽

1948 ◽

pp. 25-28

Author(s):

Andrzej Panufnik

Keyword(s):

Twentieth Century ◽

Fertile Soil ◽

Early Twentieth Century ◽

Progressive Group ◽

Karol Szymanowski

It is ten years since KAROL SZYMANOWSKI died at fifty-four. He was the most prominent representative of the “radical progressive” group of early twentieth century composers, which we call “Young Poland.” In their manysided and pioneering efforts they prepared the fertile soil on which Poland's present day's music thrives.

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