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The flutter effect in rotating machines

J. Kiciński
Bulletin of the Polish Academy of Sciences Technical Sciences | 2004 | vol. 52 | No 3 | 195-207
Keywords flutter journal bearings hydrodynamic instability rotor dynamics
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Abstract

The considerations presented in the paper relate to one of the most intriguing phenomena, which is the development of oil whirls and oil whips in rotors with journal bearings. This effect is sometimes referred to as flutter, as its origin is in some relation to self-exciting vibrations of the system. Despite the fact that the flutter has been an object of investigation in numerous research centres all over the world, its nature has not been sufficiently recognized yet. The present paper delivers a description of particular phases of development of the hydrodynamic instability and proposes diagnostic determinants for this state. The object of investigations also included bearings with hybrid lubrication and siphon pockets in the oil gaps. The answer has been received to the question whether the self-exciting vibrations in rotating machines can be avoided, or reduced by means of additional oil supply having the form of siphon oil.

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Authors and Affiliations

J. Kiciński

Research on rotary system with tilting-pad journal bearings

Vladas Vekteris Audrius Cereska
Archive of Mechanical Engineering | 2008 | vol. 55 | No 1 | 5-12 | DOI: 10.24425/ame.2008.131610
Keywords rotor system tilding-pad journal bearings frequency resonance parameters
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Abstract

This paper presents the results of research on self-vibrations of rotary systems with segmental tilting-pad journal bearings having different frequencies of rotor revolution. The problem of research formulated in this work concerns technical characteristics of primary elements of the investigated system and its principle of operation. The obtained results are illustrated with graphs. The paper also contains comparison of results and discussion. General conclusions are given at the end of the paper.

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Authors and Affiliations

Vladas Vekteris
Audrius Cereska

Transient simulation of a squeeze film damped turbocharger rotor under consideration of fluid inertia and cavitation

Thomas Drapatow Oliver Alber Elmar Woschke
Bulletin of the Polish Academy of Sciences Technical Sciences | 2021 | 69 | 6 | e139201 | DOI: 10.24425/bpasts.2021.139201
Keywords rotor dynamics journal bearings squeeze film dampers fluid inertia
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Abstract

Squeeze film dampers (SFDs) are commonly used in turbomachinery in order to introduce external damping, thereby reducing rotor vibrations and acoustic emissions. Since SFDs are of similar geometry as hydrodynamic bearings, the REYNOLDS equation of lubrication can be utilised to predict their dynamic behaviour. However, under certain operating conditions, SFDs can experience significant fluid inertia effects, which are neglected in the usual REYNOLDS analysis. An algorithm for the prediction of these effects on the pressure build up inside a finite-length SFD is therefore presented. For this purpose, the REYNOLDS equation is extended with a first-order perturbation in the fluid velocities to account for the local and convective inertia terms of the NAVIER-STOKES equations. Cavitation is taken into account by means of a mass conserving two-phase model. The resulting equation is then discretized using the finite volume method and solved with an LU factorization. The developed algorithm is capable of calculating the pressure field, and thereby the damping force, inside an SFD for arbitrary operating points in a time-efficient manner. It is therefore suited for integration into transient simulations of turbo machinery without the need for bearing force coefficient maps, which are usually restricted to circular centralized orbits. The capabilities of the method are demonstrated on a transient run-up simulation of a turbocharger rotor with two semi-floating bearings. It can be shown that the consideration of fluid inertia effects introduces a significant shift of the pressure field inside the SFDs, and therefore the resulting damper force vector, at high oil temperatures and high rotational speeds. The effect of fluid inertia on the kinematic behaviour of the whole system on the other hand is rather limited for the examined rotor.
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Bibliography

  1.  M.B. Banerjee, R. Shandil, S. Katyal, G. Dube, T. Pal, and K. Banerjee, “A nonlinear theory of hydrodynamic lubrication,” J. Math. Anal. Appl., vol. 117, no. 1, pp. 48–56, 1986.
  2.  S. Hamzehlouia and K. Behdinan, “Squeeze film dampers supporting high-speed rotors: Fluid inertia effects,” Proc. Inst. Mech. Eng., Part J: J. Eng. Tribol., vol. 234, no. 1, pp. 18–32, 2020.
  3.  M. Ramli, J. Ellis, and J. Roberts, “On the computation of inertial coefficients in squeeze-film bearings,” Proc. Inst. Mech. Eng., Part C: J. Mech. Eng. Sci., vol. 201, no. 2, pp. 125–131, 1987, doi: 10.1243/PIME_PROC_1987_201_095_02.
  4.  E. Reinhardt and J. Lund, “Influence of fluid inertia on the dynamic properties of journal bearings.” J. Lubr. Technol., vol. 97 Ser F, no. 2, pp. 159–167, 1975.
  5.  A.Z. Szeri, A.A. Raimondi, and A. Giron-Duarte, “Linear Force Coefficients for Squeeze-Film Dampers,” J. Lubr. Technol., vol. 105, no. 3, pp. 326–334, 07 1983.
  6.  A.Z. Szeri, Fluid Film Lubrication: Theory and Design. Cambridge University Press, 1998.
  7.  Z. Guo, T. Hirano, and R.G. Kirk, “Application of CFD analysis for rotating machinery: Part 1 — hydrodynamic, hydrostatic bearings and squeeze film damper,” in Volume 4: Turbo Expo 2003. ASME, 2003, doi: 10.1115/gt2003-38931.
  8.  C. Xing, M.J. Braun, and H. Li, “A three-dimensional navierstokes- based numerical model for squeeze film dampers. part 2—ef- fects of gaseous cavitation on the behavior of the squeeze film damper,” Tribol. Trans., vol. 52, no. 5, pp. 695–705, Sep 2009, doi: 10.1080/10402000902913311.
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  11.  S. Lang and S. Verlag, Effiziente Berechnung von Gleitlagern und Dichtspalten in Turbomaschinen, ser. Forschungsberichte zur Fluidsys- temtechnik. Shaker Verlag, 2018.
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Authors and Affiliations

Thomas Drapatow
1
Oliver Alber
2
Elmar Woschke
1
ORCID: ORCID
  1. Institute of Mechanics, Otto von Guericke University Magdeburg, 39106 Magdeburg, Germany
  2. MAN Energy Solutions SE, 86153 Augsburg, Germany

Active vibration damping of an asymmetric rigid rotor supported on 5-lobe journal bearings

Zbigniew Starczewski
Archive of Mechanical Engineering | vol. 48 | No 4 | 359-371
Keywords active damping journal bearings rotor self-excited vibration
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Abstract

The paper concerns efficiency of active magnetic stabilization in damping of selfexcited vibration of an asymmetric rotor supported on 5-lobe journal bearings with 5 oil gaps. The dependencies describing the pressure distribution in the oil film are presented. The components of the hydrodynamic uplift forces in the bearings are described. Equations of motion are derived using a numerical simulation method. It was found that active magnetic stabilization was effective for symmetric and non-symmetric systems. Exemplary trajectories of the journal bearing motion as well as the time histories are presented.
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Authors and Affiliations

Zbigniew Starczewski

Effect of lubricant compressibility and variable viscosity on the performance of three-lobe journal bearing

Mushrek A. Mahdi Basim Ajeel Abbas
Archive of Mechanical Engineering | 2022 | vol. 69 | No 2 | 203-219 | DOI: 10.24425/ame.2022.140412
Keywords hydrodynamic lubrication journal bearings compressibility effect variable viscosity
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Abstract

Different configurations of journal bearings have been extensively used in turbomachinery and power generating equipment. Three-lobe bearing is used due to its lower film temperature and stable operation. In this study, static performance of such a bearing has been investigated at different eccentricity ratios considering lubricant compressibility and variable viscosity. The effect of variable viscosity was considered by taking the viscosity as a function of the oil film thickness while Dowson model is used to consider the effect of lubricant compressibility. The effect of such parameters was considered to compute the oil film pressure, load-carrying capacity, attitude angle and oil side leakage for a bearing working at (ε from 0.6 to 0.8) and (viscosity coefficient from 0 to 1). The mathematical model as well as the computer program prepared to solve the governing equations were validated by comparing the pressure distribution obtained in the present work with that obtained by EL-Said et al. A good agreement between the results has been observed with maximum deviation of 3%. The obtained results indicate a decrease in oil film pressure and load-carrying capacity with the higher values of viscosity coefficient while the oil compressibility has a little effect on such parameters.
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Bibliography

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[12] P. Sinha, C. Singh, and K.R. Prasad. Effect of viscosity variation due to lubricant additives in journal bearings. Wear, 66(2):175–188, 1981. doi: 10.1016/0043-1648(81)90112-5.
[13] N.B. Naduvinamani and A.K. Kadadi. Effect of viscosity variation on the micropolar fluid squeeze film lubrication of a short journal bearing. Advances in Tribology, 2013:id743987, 2013. doi: 10.1155/2013/743987.
[14] J.R. Patel and G. Deheri. Viscosity variation effect on the magnetic fluid lubrication of a short bearing. Journal of the Serbian Society for Computational Mechanics, 13(2):56–66, 2019. doi: 10.24874/jsscm.2019.13.02.05.
[15] Q. Qu, H. Zhang, L. Zhou, and C. Wang. The analysis of the characteristics of infinitely short journal bearings modified by equivalent viscosity. 2010 International Conference on Measuring Technology and Mechatronics Automation, 754–757, 2010. doi: 10.1109/ICMTMA.2010.357.
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Authors and Affiliations

Mushrek A. Mahdi
1
ORCID: ORCID
Basim Ajeel Abbas
2
  1. University of Babylon, College of Engineering/Al-Musayab, Automobile Engineering Department, Babylon, Iraq
  2. University of Babylon, College of Engineering, Mechanical Engineering Department, Babylon, Iraq

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