Literatura académica sobre el tema "Synchronous thermal instability"
Crea una cita precisa en los estilos APA, MLA, Chicago, Harvard y otros
Consulte las listas temáticas de artículos, libros, tesis, actas de conferencias y otras fuentes académicas sobre el tema "Synchronous thermal instability".
Junto a cada fuente en la lista de referencias hay un botón "Agregar a la bibliografía". Pulsa este botón, y generaremos automáticamente la referencia bibliográfica para la obra elegida en el estilo de cita que necesites: APA, MLA, Harvard, Vancouver, Chicago, etc.
También puede descargar el texto completo de la publicación académica en formato pdf y leer en línea su resumen siempre que esté disponible en los metadatos.
Artículos de revistas sobre el tema "Synchronous thermal instability"
1
Balbahadur, A. C. y R. G. Kirk. "Part II—Case Studies for a Synchronous Thermal Instability Operating in Overhung Rotors". International Journal of Rotating Machinery 10, n.º 6 (2004): 477–87. http://dx.doi.org/10.1155/s1023621x04000478.
Texto completoResumen
In Part I, a theoretical model was developed for a synchronous thermal instability that is caused by differential viscous shearing in bearings of overhung rotors. This second part used computer programs, which were based on the theoretical model, to examine various case studies that pertain to this thermal instability. Both plain and tilting pad journal bearing rotors were examined and good agreement was found between the theoretical predictions and the practical results.
2
Balbahadur, A. C. y R. G. Kirk. "Part I—Theoretical Model for a Synchronous Thermal Instability Operating in Overhung Rotors". International Journal of Rotating Machinery 10, n.º 6 (2004): 469–75. http://dx.doi.org/10.1155/s1023621x04000466.
Texto completoResumen
Atheoretical model has been developed for a synchronous thermal instability that is caused by differential viscous shearing in bearings of overhung rotors. This model employs an unbalance threshold criterion for instability instead of utilizing a traditional frequency-domain stability analysis. The current model will be used to investigate several case studies for both plain and tilting pad journal bearing rotors in the second part of this article.
3
Singh, A. Narain, W. Doorsamy y W. A. Cronje. "Thermal Instability Analysis of a Synchronous Generator Rotor using Direct Mapping". SAIEE Africa Research Journal 109, n.º 1 (marzo de 2018): 4–14. http://dx.doi.org/10.23919/saiee.2018.8531795.
Texto completo
4
Bhadauria, Beer S., Atul K. Srivastava, Nirmal C. Sacheti y Pallath Chandran. "Gravity Modulation of Thermal Instability in a Viscoelastic Fluid Saturated Anisotropic Porous Medium". Zeitschrift für Naturforschung A 67, n.º 1-2 (1 de febrero de 2012): 1–9. http://dx.doi.org/10.5560/zna.2011-0045.
Texto completoResumen
The present paper deals with a thermal instability problem in a viscoelastic fluid saturating an anisotropic porous medium under gravity modulation. To find the gravity modulation effect, the gravity field is considered in two parts: a constant part and an externally imposed time-dependent periodic part. The time-dependent part of the gravity field, which can be realized by shaking the fluid, has been represented by a sinusoidal function. Using Hill’s equation and the Floquet theory, the convective threshold has been obtained. It is found that gravity modulation can significantly affect the stability limits of the system. Further, we find that there is a competition between the synchronous and subharmonic modes of convection at the onset of instability. Effects of various parameters on the onset of instability have also been discussed.
5
Balbahadur, A. y R. Kirk. "Part I?Theoretical Model for a Synchronous Thermal Instability Operating in Overhung Rotors". International Journal of Rotating Machinery 10, n.º 6 (1 de noviembre de 2004): 469–75. http://dx.doi.org/10.1080/10236210490504021.
Texto completo
6
Balbahadur, A. y R. Kirk. "Part II?Case Studies for a Synchronous Thermal Instability Operating in Overhung Rotors". International Journal of Rotating Machinery 10, n.º 6 (1 de noviembre de 2004): 477–87. http://dx.doi.org/10.1080/10236210490504067.
Texto completo
7
Olsson, Karl-Olof. "Some Unusual Cases of Rotor Instability". Journal of Vibration and Acoustics 125, n.º 4 (1 de octubre de 2003): 477–81. http://dx.doi.org/10.1115/1.1606692.
Texto completoResumen
In the paper presented here three peculiar cases of rotor instability are presented. The first is a tilting-pad bearing used as an intershaft bearing in a two-spool gas turbine. It was initially chosen for its good stability properties. However, in a deeper study it was found that those benefits are greatly reduced when both inner shaft and outer bearing are rotating. The second case comprises a turbine which showed a very strange performance with vibrations alternating between heavy and mild amplitudes. The periods were a couple of minutes long. After a more elaborate instrumentation was installed it was found that vibrations were synchronous and that the rotor experienced continuous changes of vibrations interrupted by sudden changes of amplitude. This revealed that nonlinearity and thermal effects coupled to the rotor vibrations must be incorporated to understand the behavior. Many hypotheses were tested and the one coming closest to explaining the case was one incorporating thermal bending caused by heat conduction through an annulus partly filled with oil. The third case is a simple one of more pure curiosity, where a rotor was provided with a substantial amount of inner damping, and just according to the school book showed dynamic instability.
8
Yoshida, Yoshiki, Yoshifumi Sasao, Kouichi Okita, Satoshi Hasegawa, Mitsuru Shimagaki y Toshiaki Ikohagi. "Influence of Thermodynamic Effect on Synchronous Rotating Cavitation". Journal of Fluids Engineering 129, n.º 7 (10 de enero de 2007): 871–76. http://dx.doi.org/10.1115/1.2745838.
Texto completoResumen
Synchronous rotating cavitation is known as one type of cavitation instability, which causes synchronous shaft vibration or head loss. On the other hand, cavitation in cryogenic fluids has a thermodynamic effect on cavitating inducers because of thermal imbalance around the cavity. It improves cavitation performances due to delay of cavity growth. However, relationships between the thermodynamic effect and cavitation instabilities are still unknown. To investigate the influence of the thermodynamic effect on synchronous rotating cavitation, we conducted experiments in which liquid nitrogen was set at different temperatures (74K, 78K, and 83K). We clarified the thermodynamic effect on synchronous rotating cavitation in terms of cavity length, fluid force, and liquid temperature. Synchronous rotating cavitation occurs at the critical cavity length of Lc∕h≅0.8, and the onset cavitation number shifts to a lower level due to the lag of cavity growth by the thermodynamic effect, which appears significantly with rising liquid temperature. Furthermore, we confirmed that the fluid force acting on the inducer notably increases under conditions of synchronous rotating cavitation.
9
Bhadauria, B. S. "Unsteady Heating of Rayleigh-Benard Convection". Zeitschrift für Naturforschung A 59, n.º 4-5 (1 de mayo de 2004): 266–74. http://dx.doi.org/10.1515/zna-2004-4-511.
Texto completoResumen
The linear thermal instability of a horizontal fluid layer with time-periodic temperature distribution is studied with the help of the Floquet theory. The time-dependent part of the temperature has been expressed in Fourier series. Disturbances are assumed to be infinitesimal. Only even solutions are considered. Numerical results for the critical Rayleigh number are obtained at various Prandtl numbers and for various values of the frequency. It is found that the disturbances are either synchronous with the primary temperature field or have half its frequency. - 2000 Mathematics Subject Classification: 76E06, 76R10.
10
OR, A. C. y R. E. KELLY. "The effects of thermal modulation upon the onset of Marangoni–Bénard convection". Journal of Fluid Mechanics 456 (9 de abril de 2002): 161–82. http://dx.doi.org/10.1017/s0022112001007510.
Texto completoResumen
The effects of thermal modulation with time on the thermocapillary instability of a thin horizontal fluid layer with a deformable free surface are investigated on the basis of linear stability theory. First, a sinusoidal heating with a mean component is applied at the lower wall, corresponding to boundary conditions either in the form of prescribed temperature or heat flux. For finite-wavelength convection the thermal modulation exerts a strong effect, giving rise to a family of looped regions of instability corresponding to alternating synchronous or subharmonic responses. In the case of prescribed heat flux, the critical curve consists of significantly fewer loops than in the case of prescribed temperature. Thermal modulation with moderate modulation amplitude tends to stabilize the mean basic state, and optimal values of frequency and amplitude of modulation are determined to yield maximum stabilization. However, large-amplitude modulation can be destabilizing. A basic state with zero mean is then considered and the critical Marangoni number is obtained as a function of frequency. The effects of modulation are also investigated in the long-wavelength limit. For the case of prescribed temperature, the modulation does not affect the onset of the long-wavelength mode associated with the mean basic state and a purely oscillating basic state is always stable with respect to long-wavelength disturbances. For the case of prescribed heat flux both at the wall and free surface, by contrast, thermal modulation exerts a significant effect on the onset of convection from a mean basic state and long-wavelength convection can occur even for a purely oscillating basic state. The modulation can be stabilizing or destabilizing, depending on the frequency.
Tesis sobre el tema "Synchronous thermal instability"
1
Carroll, Brian R. "Synchronous Thermal Instability Evaluation of Medium Speed Turbocharger Rotor-Bearing Systems". Thesis, Virginia Tech, 2012. http://hdl.handle.net/10919/32886.
Texto completoResumen
Rotors in fluid-film bearing supported turbomachinery are known to develop elliptical orbits as a result of rotor-bearing interactions, mass unbalance within the rotor, gravitational bending of the shaft and external excitation. In synchronous whirl, where the speed at which the shaft travels about the orbit is equal to the rotational speed of the rotor, temperature gradients may develop across the journal as a result of viscous shear in the bearingâ s lubricant film. This thermal gradient leads to bending of the shaft in a phenomenon known as The Morton Effect. Such thermally induced bending causes further growth of the elliptical orbit resulting in further bending leading to excessive vibration levels and premature bearing failure. This analysis examines the development of the Morton Effect in medium-speed turbochargers typical to shipboard propulsion engines and the effect that bearing clearance has on thermal stability. Floating ring and tilting pad journal bearings are considered with a single stage, overhung centrifugal compressor and an overhung axial turbine. Results indicate a correlation between bearing clearance and thermal stability in the rotor-bearing system.
A model for the aerodynamic force generated as a result of interaction between air exiting a centrifugal compressor and the compressorâ s annulus in a turbocharger is then developed and applied to the rotor-bearing systems. Results suggest little correlation between this aerodynamic force and the development of the Morton Effect.Master of Science
2
Zhang, Silun. "Analyse de l'effet Morton dans les turbines à vapeur". Thesis, Poitiers, 2019. http://www.theses.fr/2019POIT2260.
Texto completoResumen
Dans le domaine de machine tournante (turbines à vapeurs, turbocompresseurs et autres turbomachines), l’effet Morton désigne la création d’une source d’excitation synchrone due à la déformation thermique du rotor dans les paliers hydrodynamiques. Par abus de langage, cette source phase des vibrations synchrones du rotor évoluent progressivement dans le temps. Dans la plupart des cas, l’effet Morton reste stable et les influences du balourd thermique sur les vibrations ne sont pas nuisibles au fonctionnement de la machine. Cependant, si les conditions sont favorables, le comportement dynamique du rotor devient instable et l’instabilité de la vibration synchrone, autrement dit l’effet Morton, pourrait se produire.Pour mieux comprendre et analyser les conditions du déclenchement de ce scénario destructif, il est nécessaire de simuler l’effet Morton de manière précise. Cette simulation nécessite de faire intervenir plusieurs phénomènes physiques et coupler plusieurs modèles mathématiques. Ce sont le modèle de la lubrification hydrodynamique, le modèle thermomécanique du rotor et le modèle de la dynamique du rotor. Ce couplage multi-physique n’est pas simple à cause des échelles de temps différentes du phénomène thermomécanique et de la dynamique du rotor. La stratégie du flux thermique moyenné sur une période de rotation permet de surmonter cette difficulté et de réduire le temps de calcul. La modélisation de l’effet Morton est validée par une confrontation entre les résultats numériques et les résultats expérimentaux obtenus à l’Institut Pprime.Une méthode basée sur les coefficients d’influence est ensuite exploitée pour analyser la stabilité de l’effet Morton. Les applications de cette méthode sur des cas concrets permettent de mettre en évidence les phénomènes physiques responsable de l’effet Morton instableIn the field of rotating machines (steam turbines, turbochargers and other turbomachines), the Morton effect designates the creation of a synchronous excitation source due to the thermal deformation of the rotor in the hydrodynamic bearings. By abuse of language, this vibratory source is often called thermal unbalance. Under the effect of this imbalance, the amplitude and the phase of the synchronous vibrations of the rotor evolve gradually over time. In most cases, the Morton effectremains stable and the effects of thermal unbalance on the vibrations are not detrimental to the operation of the machine. However, if the conditions are favorable, the dynamic behavior of the rotor becomes unstable and the instability of the synchronous vibration, in other words the Morton effect, could occur.To better understand and analyze the triggering conditions of this destructive scenario, it is necessary to simulate the Morton effect accurately. This simulation requires several physical phenomena and to couple several mathematical models. These are the model of hydrodynamic lubrication, the thermomechanical model of the rotor and the model of rotor dynamics. This multiphysics coupling is not simple because of the different time scales of the thermomechanical phenomenon and the rotor dynamics. The strategy of heat flux averaged over a rotation period makes it possible to overcome this difficulty and to reduce the calculation time. The modeling of the Morton effect is validated by a comparison between the numerical results and the experimental resultsobtained at the Pprime Institute.A method based on the influence coefficients is then used to analyze the stability of the Morton effect. The applications of this method on concrete cases make it possible to highlight the physical phenomena responsible for the unstable Morton effect
3
GRIFFINI, DUCCIO. "Development of Predictive Models for Synchronous Thermal Instability". Doctoral thesis, 2017. http://hdl.handle.net/2158/1081044.
Texto completoResumen
The increasing demand of higher efficiency and increased equipment compactness is pushing the modern rotordynamic design towards higher and higher bearing peripheral speed. Due to the increased viscous dissipation, modern fluid film bearings are prone to the development of complex thermal phenomena that, under certain conditions, can result in synchronous thermal instability, often referred to as Morton effect. Although the phenomenon is known and studied from the late 1970s a lack of knowledge is highlighted in literature and the strategy to approach its prediction and analysis is yet debated within the scientific community. This work presents the development and validation of the numerical models for the prediction of the synchronous thermal instability. The proposed models are derived from a preliminary analysis of the physical time scales of the problem and of the orders of magnitude of the equations, which allowed an aware selection of the modelling strategies from a dual point of view: the physical genesis of the Morton effect (i.e., the
differential heating of the shaft) and the assessment of the stability of the rotor-bearing system under the influence of the thermal effects. Particular focus is devoted to the fluid-dynamical problem with the description of two dedicated codes, developed, respectively, for the analysis of the thermo-hydrodyanmics of fluid film bearings and for the modelling of the differential temperature developed across the shaft. This latter phenomenon is due to the differential heating and results to be the driving parameter of the problem. Once the two codes has been individually validated, these have been inserted in more complex systems in order to evaluate their ability to enable the prediction of the Morton effect. A linear stability analysis has been firstly performed and results, although affected by discrepancies with respect to the experimental data, have shown the potential of the codes to reach the objective of the work. Better results have been finally obtained when the models have been inserted in a more complex architecture. This latter has been developed in collaboration with the MDMlab of the Department of Industrial Engineering of the University of Florence in order to model the synchronous thermal instability by means of an iterative approach. A comparison with available experimental data, derived from a dedicated test campaign carried out at the GE Oil & Gas facility in Florence, is shown in order to validate both the procedure and the models. Moreover, some key parameters driving the Morton effect are presented and a study of the sensitivity of the phenomenon to the thermal expansion coefficient is proposed in order to improve researchers’
knowledge on the topic.
4
Narain, Singh Amesh. "Investigation into high-speed thermal instability testing of synchronous turbo-generator rotors". Thesis, 2017. https://hdl.handle.net/10539/24190.
Texto completoResumen
A thesis submitted to the Faculty of Engineering, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy.
Johannesburg, 2017The research presented in this thesis conclusively shows that the most effective method to perform synchronous turbo-generator rotor Thermal Instability Testing is by utilising the current injection method of condition assessment. Analysis of the experiences of a local utility for well over a decade has uncovered a high number of rotors failing thermal instability testing in recent years. This trend has brought the current testing methodology into question. Two different assessment modes of testing have been found to be utilised internationally without preference, namely, current injection and friction/windage. By determining the method that is best suited to detect a thermally sensitive rotor a service provider can benefit by improved rotor reliability as well as cost saving. The evaluation is accomplished by utilising a scaled down experimental setup based on the model of a local testing facility as well as a 600 MW turbo-generator rotor. A direct thermal mapping technique has been devised utilising infrared thermography to capture the thermal distribution of the rotor surface under different test conditions. The results obtained have shown that the methods differ substantially with the friction method exhibiting a uniform surface distribution and the current-injection method exhibiting areas of higher temperature concentration around the rotor pole faces. However, weaknesses do exist in present-day testing techniques in the form of inaccurate temperature measurements during testing as well as little consideration given to external factors such as the interaction between the slip-ring and brush-gear that have the potential to influence test outcomes. A presented augmented method of performing thermal sensitivity testing taking advantage of infrared thermography is found to improve testing accuracy and aid in fault detection and location. Current thermal instability testing coupled with the direct thermal mapping method has been demonstrated to be the most effective means for performing rotor thermal sensitivity testing.
MT2018
Actas de conferencias sobre el tema "Synchronous thermal instability"
1
Kirk, R. Gordon y Zenglin Guo. "Design Tool for Prediction of Thermal Synchronous Instability". En ASME 2013 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/detc2013-12966.
Texto completoResumen
The investigation of thermal synchronous instability has been active since the mid 1990’s and the number of machines experiencing this type of instability continues to rise. The initial design threshold speed criteria was developed and compared to available case studies during 1998–2001. Further advances were made from 2002–2007 in the prediction of the bearing journal thermal hot spot in addition to improved pre and post processing capability. These improvements made the design tool more useful for prediction of thermal synchronous instability for shaft overhangs. More recent work reported in 2011, extended the theory to treat rotor center-span instability, but the interest in shaft overhang instability is still dominant from a practical view. This paper will document a new threshold speed criteria being used in a modified design tool that is considered to be more realistic for a wider range of operating speed conditions. The paper will discuss the improved threshold criteria and illustrate why it is a more reliable design tool.
2
Shin, Dongil, Alan B. Palazzolo y Xiaomeng Tong. "Squeeze Film Damper Suppression of Thermal Bow: Morton Effect Instability". En ASME Turbo Expo 2020: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/gt2020-14825.
Texto completoResumen
Abstract The Morton Effect (ME) is a synchronous vibration problem in turbomachinery caused by the non-uniform viscous heating around the journal circumference, and its resultant thermal bow and ensuing synchronous vibration. This paper treats the unconventional application of the SFD for the mitigation of ME-induced vibration. Installing a properly designed squeeze film damper (SFD) may change the rotor’s critical speed location, damping and deflection shape, and thereby suppress the vibration caused by the ME. The effectiveness of the SFD on suppressing the ME is tested via linear and nonlinear simulation studies employing a 3D thermo-hydrodynamic (THD) tilting pad journal bearing, and a flexible, Euler beam rotor model. The example rotor model is for a compressor that experimentally exhibited an unacceptable vibration level along with significant journal differential heating near 8,000 rpm. The SFD model includes fluid inertia and is installed on the non-drive end bearing location where the asymmetric viscous heating of the journal is highest. The influence of SFD cage stiffness is evaluated.
3
Singh, A. Narain, W. A. Cronje y W. Doorsamy. "Investigation of thermal instability testing on synchronous generator rotors using an experimental direct mapping method". En 2017 IEEE 26th International Symposium on Industrial Electronics (ISIE). IEEE, 2017. http://dx.doi.org/10.1109/isie.2017.8001267.
Texto completo
4
Faulkner, H. B., W. F. Strong y R. G. Kirk. "Thermally Induced Synchronous Instability of a Radial Inflow Overhung Turbine: Part II". En ASME 1997 Design Engineering Technical Conferences. American Society of Mechanical Engineers, 1997. http://dx.doi.org/10.1115/detc97/vib-4174.
Texto completoResumen
Abstract This paper is in two parts, and concerns the lateral dynamics of a large turbocharger rotor with overhung wheels. Initial rotor dynamic analysis indicated no excessive motion in the operating speed range. However, testing showed excessive motion, which was initially traced to the radial-inflow turbine wheel becoming loose on the shaft, due to transient differential thermal expansion in the wheel on startup. The attachment of the wheel was modified to eliminate this problem. The discussion up to this point is in Part I of the paper, and the remainder is in Part II. The wheel attachment modification extended the range of satisfactory operation upward considerably, but excessive lateral motion was again encountered near the upper end of the operating speed range. This behavior was traced to thermal bowing of the shaft at the turbine end, known as the Morton Effect. The turbine end bearing was modified to eliminate this problem, and satisfactory operation was then achieved throughout the operating speed range.
5
Faulkner, H. B., W. F. Strong y R. G. Kirk. "Thermally Induced Synchronous Instability of a Radial Inflow Overhung Turbine: Part I". En ASME 1997 Design Engineering Technical Conferences. American Society of Mechanical Engineers, 1997. http://dx.doi.org/10.1115/detc97/vib-4063.
Texto completoResumen
Abstract This paper is in two parts, and concerns the lateral dynamics of a large turbocharger rotor with overhung wheels. Initial rotor dynamic analysis indicated no excessive motion in the operating speed range. However, testing showed excessive motion, which was initially traced to the radial-inflow turbine wheel becoming loose on the shaft, due to transient differential thermal expansion in the wheel on startup. The attachment of the wheel was modified to eliminate this problem. The discussion up to this point is in Part I of the paper, and the remainder is in Part II. The wheel attachment modification extended the range of satisfactory operation upward considerably, but excessive lateral motion was again encountered near the upper end of the operating speed range. This behavior was traced to thermal bowing of the shaft at the turbine end, known as the Morton Effect. The turbine end bearing was modified to eliminate this problem, and satisfactory operation was then achieved throughout the operating speed range.
6
Guo, Zenglin y Gordon Kirk. "Morton Effect Induced Synchronous Instability in Mid-Span Rotor-Bearing Systems: Part 1—Mechanism Study". En ASME 2010 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. ASMEDC, 2010. http://dx.doi.org/10.1115/detc2010-28341.
Texto completoResumen
The Morton Effect in the rotor–bearing systems may lead to an unstable operation. In Part 1, the mechanism of the Morton Effect induced thermal instability in the mid-span rotor systems has been studied. First, the equivalent thermal induced imbalance is introduced and its magnitude and directions are assumed, to represent the viscous thermal effect on the rotor systems. Then, the simplified rotor and bearing models are adopted for the derivation of analytical expressions. The results show that there exists a threshold of instability due to the Morton Effect in the mid-span rotors. Based on the assumptions of linear isotopic bearing supports, this threshold speed takes a simple form, which is determined by the support stiffness and the introduced equivalent coefficient of thermal effect, for the rigid or elastic systems with the thermal imbalance acting in the same direction as the response displacement. The threshold of instability has also been obtained for the system with the thermal imbalance acting perpendicular to the direction of response displacement, where the supporting damping plays a role. For a perspective view of the system stability, a stability map for the damped rigid mid-span rotors with the thermal imbalance having arbitrary phase difference has been generated. It shows that the stable operating regions of the system are bounded by two curves of threshold of instability, named the first and second threshold speeds of instability, respectively. The Morton Effect induced instability thresholds are actually affected by both the magnitude and relative phase of the thermal imbalance. The mechanism of the Morton Effect induced thermal instability of mid-span rotors supported by linear isotropic bearings can be explained through the fact that the Morton Effect introduces either negative stiffness or negative cross-coupled stiffness. In addition, the Morton Effect also has a comprehensive impact on both the amplitude and phase lag of the steady-state unbalance response. It may shift both curves in a manner dependent on the relative magnitude and direction of the thermal imbalance.
7
Olsson, Karl-Olof. "Some Unusual Cases of Rotor Instability". En ASME 2001 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. American Society of Mechanical Engineers, 2001. http://dx.doi.org/10.1115/detc2001/vib-21375.
Texto completoResumen
Abstract In the paper presented here three peculiar cases of rotor instability are presented. The first is a tilting-pad bearing used as an intershaft bearing in a two-spool gas turbine. It was initially chosen for its good stability properties. However, in a deeper study it was found that those benefits are greatly reduced when both inner shaft and outer bearing are rotating. The second case comprises a turbine which showed a very strange performance with vibrations alternating between heavy and mild amplitudes. The periods were a couple of minutes long. After a more elaborate instrumentation was installed it was found that vibrations were synchronous and that the rotor experienced continuos changes of vibrations interrupted by sudden changes of amplitude. This revealed that non-linearity and thermal effects coupled to the rotor vibrations must be incorporated to understand the behavior. Many hypotheses were tested and the one coming closest to explaining the case was one incorporating thermal bending caused by heat conduction through an annulus partly filled with oil. The third case is a simple one of more pure curiosity, where a rotor was provided with a substantial amount of inner damping, and just according to the school book showed dynamic instability.
8
Berot, François y Hervé Dourlens. "On Instability of Overhung Centrifugal Compressors". En ASME 1999 International Gas Turbine and Aeroengine Congress and Exhibition. American Society of Mechanical Engineers, 1999. http://dx.doi.org/10.1115/99-gt-202.
Texto completoResumen
This paper describes the synchronous vibration instability problem that occurred on a series of large overhung centrifugal compressors. The first part of this paper deals with the identification and display of the instability phenomenon: cyclic vibration amplitude variations and phase angle rotation occuring during testing of overhung centrifugal compressors. After numerical simulations and analysis of the test results, the bearing design has been identified as the cause of the problem. The second part describes the numerical study of the instability of the compressor. This problem is related to the eccentricity of the shaft in the bearing and to the shape of its orbit. We have investigated and propose different solutions to avoid this unstable dynamic behavior. These solutions have been tested on different compressors and have confirmed the results of the numerical analysis. The third part reminds a link between the thermal effect occurring in the bearings, the numerical results and the tested dynamic behavior of the compressor. Recently, some authors such as Keogh et al. (1994) and Liebich et al. (1994) have noticed and studied this unstable behavior. Althougth the nature of the phenomenon seems to be known (de Jongh et al., 1984) (Faulkner et al., 1997a, 1997b), no universal technical solution to this important problem has been found. The contribution of this work is to present another case of the influence of the thermal effect on the dynamic behavior of an overhung compressor. We present the typical symptoms of the phenomenon, explain it, and propose the solutions we have used to avoid the problem.
9
Kirk, Gordon. "Rotating Machinery Long Coupling Spacer Related Vibration". En ASME 2015 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/detc2015-46718.
Texto completoResumen
The increased speed and power level of rotating machinery most often bring the problem of non-synchronous instability. Many of the current most interesting problems, have been caused by synchronous thermal instability. These problems are related to the machinery overhangs predominantly, many are due to heavy couplings and the associated fluid film bearing non-uniform heating of the rotor shaft coupling end journal area. For couplings with long spacer tubes, other causes of excessive synchronous vibration are worthy of discussion. Long coupling spacer tubes with balance correction made at low speed and operating in service too near the coupling spacer critical speed can result in excessive synchronous vibration. Once the spacer has large mid-span amplitude, additional nonlinear vibration can occur. This paper discusses a recent occurrence of this interesting problem and will show why it should not be overlooked in future coupled multi-body high speed machinery trains, or any driveshaft balanced only at the shaft end plains.
10
Guo, Zenglin y Gordon Kirk. "Morton Effect Induced Synchronous Instability in Mid-Span Rotor-Bearing Systems: Part 2—Models and Simulations". En ASME 2010 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. ASMEDC, 2010. http://dx.doi.org/10.1115/detc2010-28342.
Texto completoResumen
The mechanism of the Morton Effect induced synchronous instability has been discussed in Part 1, using an assumption of isotropic linear bearings. The second part of the current study will now focus on the more realistic systems, mid-span rotors supported by the hydrodynamic journal bearings. First, the models to calculate the thermal bending of the shaft and the temperature distribution across the journal surface are established. This can be used to calculate the equivalent thermal imbalance. The calculations of the temperature difference and its equivalent thermal imbalance using hydrodynamic plain journal bearing models are conducted and discussed with the comparison to the analytical results obtained in Part 1. It shows that the thermal imbalance induced by the Morton Effect may increase to the level of the mechanical imbalance and then its influence on the system stability should be included. The suggested thermal bending model also partially explain that the mid-span rotors are less liable to be influenced by the Morton Effect induced instability than are the overhung configurations, because of the restraining effect between two supports. Finally, a symmetric mid-span rotor–hydrodynamic journal bearing system is calculated to show its stability performance. The results show the inclusion of the Morton Effect may lead to an unstable operation of the system. Considering the existence of the oil film self-induced vibration due to the dynamic characteristics of fluid film bearings, the Morton Effect may make a further negative impact on the stability of the system. The simulation results of the unbalance response show that the Morton Effect changes the shapes of the whirling orbits and makes them no longer be the standard elliptical orbits around the static equilibriums.