Experimental Analysis of the Unbalance Response of Rigid Rotors Supported on Aerodynamic Foil Bearings

2015 ◽  
Vol 137 (6) ◽  
Author(s):  
Franck Balducchi ◽  
Mihai Arghir ◽  
Romain Gauthier
Keyword(s):  
Vibration Spectrum ◽  
Rotation Speed ◽  
Nonlinear Behavior ◽  
Structural Damping ◽  
Foil Bearings ◽  
Unbalance Response ◽  
Theoretical Predictions ◽  
Air Film ◽  
Rigid Rotors ◽  
Cubic Stiffness

The paper presents the experimental unbalance response of two slightly different rigid rotors supported by aerodynamic foil bearings. Impulse (Pelton) turbines manufactured directly in the mass of the rotors (on the outer surface) entrain both rotors at rotation speeds comprised between 50 krpm and 100 krpm. The displacements in the two foil bearings are measured during coast down and are depicted as waterfall plots. They show typical nonlinear behavior, i.e., subsynchronous vibrations accompanying the synchronous component. The measurements clearly show that the subsynchronous components bifurcate or jump at typical rotation speeds (mostly rational fractions of the rotation speed). The nonlinear behavior of the rigid rotor supported on foil bearings is also emphasized by varying the added unbalance: with increasing unbalance the vibration spectrum becomes gradually more diverse as new subsynchronous vibrations appear. The experimental results are compared with very simplified theoretical predictions based on the assumption that the air film in the two bearings is infinitely stiff compared to the foil structure. The latter is characterized by a cubic stiffness and a structural damping coefficient. The comparisons show only a rough qualitative agreement.

Experimental Analysis of the Unbalance Response of Rigid Rotors Supported on Aerodynamic Foil Bearings

2014 ◽  
Author(s):  
Franck Balducchi ◽  
Mihai Arghir ◽  
Sylvain Gaudillere
Keyword(s):  
Theoretical Models ◽  
Structural Damping ◽  
Foil Bearings ◽  
Unbalance Response ◽  
Linear Behavior ◽  
Non Linear ◽  
Theoretical Predictions ◽  
Air Film ◽  
Rigid Rotors ◽  
Cubic Stiffness

The paper presents the experimental unbalance response of two slightly different rigid rotors supported by two identical aerodynamic foil bearings. Impulse (Pelton) turbines manufactured directly on the outer surface entrain both rotors at rotation speeds comprised between 50 krpm and 100 krpm. The displacements in the two foil bearings are measured during coast down and are depicted as waterfall plots. They show typical non-linear behavior, i.e. subsynchronous vibrations accompanying the synchronous component. The measurements show clearly that the subsynchronous components bifurcate at typical rotation speeds (mostly rational fractions of the rotation speed). The non-linear behavior of the rigid rotor supported on foil bearings is also underlined by varying the added unbalance: with increasing unbalance the vibration spectrum becomes gradually richer as new subsynchronous vibrations appear. The experimental results are compared with very simplified theoretical predictions based on the assumption that the air film in the two bearings is infinitely stiff compared to the foil structure. This latter is characterized by a cubic stiffness and a structural damping coefficient. The comparisons show only a rough qualitative agreement and enlighten the actual limits of foil bearings theoretical models.

scholarly journals Analysis of the dynamic characteristics of downsized aerostatic thrust bearings with different pressure equalizing grooves at high or ultra-high speed

2021 ◽  
Vol 13 (5) ◽  
pp. 168781402110180
Author(s):  
Ruzhong Yan ◽  
Haojie Zhang
Keyword(s):  
Dynamic Characteristics ◽  
High Speed ◽  
Rotation Speed ◽  
Dynamic Stiffness ◽  
Simulation Method ◽  
Perturbation Amplitude ◽  
Thrust Bearings ◽  
Supply Pressure ◽  
Ultra High Speed ◽  
Air Film

This study adopts the DMT(dynamic mesh technology) and UDF(user defined functions) co-simulation method to study the dynamic characteristics of aerostatic thrust bearings with equalizing grooves and compare with the bearing without equalizing groove under high speed or ultra high speed for the first time. The effects of air film thicness, supply pressure, rotation speed, perturbation amplitude, perturbation frequency, and cross section of the groove on performance characteristics of aerostatic thrust bearing are thoroughly investigated. The results show that the dynamic stiffiness and damping coefficient of the bearing with triangular or trapezoidal groove have obvious advantages by comparing with that of the bearing without groove or with rectangular groove for the most range of air film thickness, supply pressure, rotation speed, perturbation amplitude, especially in the case of high frequency, which may be due to the superposition of secondary throttling effect and air compressible effect. While the growth range of dynamic stiffness decreases in the case of high or ultra-high rotation speed, which may be because the Bernoulli effect started to appear. The perturbation amplitude only has little influence on the dynamic characteristic when it is small, but with the increase of perturbation amplitude, the influence becomes more obvious and complex, especially for downsized aerostatic bearing.

Theoretical Prediction of the Lift-Off Speed in Aerodynamic Compliant Foil Journal Bearings

2010 ◽  
Author(s):  
Shemiao Qi ◽  
Y. S. Ho ◽  
Haipeng Geng ◽  
Lie Yu
Keyword(s):  
Theoretical Prediction ◽  
Generalized Solution ◽  
Journal Bearings ◽  
Numerical Results ◽  
Computational Method ◽  
Radial Clearance ◽  
Eccentricity Ratio ◽  
Foil Bearings ◽  
Lift Off ◽  
Air Film

In aerodynamic bearings, since the supporting air film is generated by rotor motion, there is no support at the start of motion. As in all such bearings, there is dry rubbing until the rotor achieves sufficient speed to lift-off. Thus, the lower the lift-off speed, the less will be the rubbing and so the greater will be the life of the bearing. This paper focuses on the theoretical prediction of lift-off speed in aerodynamic compliant foil journal bearings based on a generalized solution of elasto-aerodynamically coupled lubrication for compliant foil bearings. A computational method is presented which is used to predict the lift-off speed in aerodynamic foil journal bearings with eccentricity ratio greater than or equal to 1.0. Special emphasis is placed on investigating the effects of the load imposed on the bearing, the nominal radial clearance and the bearing radius on the lift-off speed. The numerical results obtained indicate that lift-off speed decreases with the decrease of load and nominal radial clearance, but with an increase in bearing radius. The eccentricity ratios are all greater than 1.0 at the lift-off speed for the aerodynamic compliant foil journal bearings used in this study.

Stability analysis of rigid rotors supported by gas foil bearings coupled with electromagnetic actuators

2019 ◽  
Vol 234 (2) ◽  
pp. 427-443 ◽  
Author(s):  
Kamal Kumar Basumatary ◽  
Gaurav Kumar ◽  
Karuna Kalita ◽  
Sashindra K Kakoty
Keyword(s):  
Stability Analysis ◽  
Equations Of Motion ◽  
Electromagnetic Actuator ◽  
Electromagnetic Actuators ◽  
Foil Bearings ◽  
Damping Characteristics ◽  
Foil Bearing ◽  
Model Combining ◽  
The Stability ◽  
Rigid Rotors

Rotors supported on gas foil bearings have low damping characteristics, which limits its application. A possible solution could be an integration of a gas foil bearing with an electromagnetic actuator. This paper discusses the effect of electromagnetic actuators on the stability of a rotor supported on gas foil bearings. A coupled dynamic model combining the dynamics of gas foil bearing and electromagnetic actuator has been developed. The fluid film forces from the gas foil bearings and the electromagnetic forces from the electromagnetic actuators are integrated into the equations of motion of the rotor. The sub-synchronous vibration present in case of conventional gas foil bearings is reduced and the stability band of the rotor is increased due to the implementation of electromagnetic actuator.

On the Instability Mechanisms of a Disk Rotating Close to a Rigid Surface

1995 ◽  
Vol 62 (3) ◽  
pp. 764-771 ◽  
Author(s):  
F. Y. Huang ◽  
C. D. Mote
Keyword(s):  
Rotation Speed ◽  
Maximum Speed ◽  
Film System ◽  
Rigid Surface ◽  
Flow Component ◽  
Flutter Speed ◽  
Disk Rotation ◽  
Viscous Shear ◽  
Air Film ◽  
Disk Rotation Speed

The instability mechanisms of a rotating disk, coupled to a rigid surface through a viscous fluid film at the interface, are investigated analytically. The fluid in the film is driven circumferentially by the viscous shear, and it flows outwards radially under centrifugal forces. The circumferential flow component creates an equivalent viscous damping rotating at one half the disk rotation speed. This film damping dissipates all backward traveling waves where the undamped wave speeds are greater than one half the disk rotation speed. The radial flow component creates a nonsymmetric stiffness in the disk-film system that energizes any wave mode at rotation speeds above its flutter speed. Instabilities in the disk-film system are of two types. A rotating damping instability is caused by the rotating film damping at rotation speeds above a critical value that is less than the flutter speed. A combination instability is caused by the combined effect of the film stiffness and damping at rotation speeds above a threshold that is greater than the flutter speed. The maximum rotation speed of stable disk vibration is bounded above by the lowest onset speed of rotating damping instability. This speed limit is predicted for two wall enclosure designs. The maximum stable rotation speed of a 5.25-inch diameter flexible, memory disk, separated from a rigid surface by a viscous air film, is shown to be more than 15 times greater than the maximum speed of the disk without the air film.

A Contribution to the Thermal Modeling of Bump Type Air Foil Bearings: Analysis of the Thermal Resistance of Bump Foils

2017 ◽  
Vol 139 (6) ◽  
Author(s):  
Andreas Lehn ◽  
Marcel Mahner ◽  
Bernhard Schweizer
Keyword(s):  
Thermal Resistance ◽  
Thermal Contact ◽  
Applied Pressure ◽  
Analytical Formula ◽  
Base Plate ◽  
Air Gaps ◽  
Foil Bearings ◽  
Foil Bearing ◽  
Air Film ◽  
Good Agreement

A detailed analysis of the effective thermal resistance for the bump foil of air foil bearings (AFBs) is performed. The presented model puts emphasis on the thermal contact resistances between the bump foil and the top foil as well as between the bump foil and the base plate. It is demonstrated that most of the dissipated heat in the lubricating air film of an air foil bearing is not conducted by microcontacts in the contact regions. Instead, the air gaps close to the contact area are found to be thin enough in order to effectively conduct the heat from the top foil into the bump foil. On the basis of these findings, an analytical formula is developed for the effective thermal resistance of a half bump arc. The formula accounts for the geometry of the bump foil as well as for the surface roughness of the top foil, the bump foil, and the base plate. The predictions of the presented model are shown to be in good agreement with measurements from the literature. In particular, the model predicts the effective thermal resistance to be almost independent of the applied pressure. This is a major characteristic property that has been found by measurements but could not be reproduced by previously published models. The presented formula contributes to an accurate thermohydrodynamic (THD) modeling of AFBs.

Modal Analysis of Ballooning Strings With Small Sag

1999 ◽  
Author(s):  
Rongjun Fan ◽  
Sushil K. Singh ◽  
Christopher D. Rahn
Keyword(s):  
Steady State ◽  
High Speed ◽  
Natural Frequencies ◽  
Rotation Speed ◽  
Equations Of Motion ◽  
Three Dimensional ◽  
Mode Shapes ◽  
Theoretical Predictions ◽  
Nonlinear Equations Of Motion

Abstract During the manufacture and transport of textile products, yarns are rotated at high speed and form balloons. The dynamic response of the balloon to varying rotation speed, boundary excitation, and disturbance forces governs the quality of the associated process. Resonance, in particular, can cause large tension variations that reduce product quality and may cause yarn breakage. In this paper, the natural frequencies and mode shapes of a single loop balloon are calculated to predict resonance. The three dimensional nonlinear equations of motion are simplified via small steady state displacement (sag) and vibration assumptions. Axial vibration is assumed to propagate instantaneously or in a quasistatic manner. Galerkin’s method is used to calculate the mode shapes and natural frequencies of the linearized equations. Experimental measurements of the steady state balloon shape and the first two natural frequencies and mode shapes are compared with theoretical predictions.

scholarly journals Stability of rigid rotors supported by air foil bearings: Comparison of two fundamental approaches

2016 ◽  
Vol 381 ◽  
pp. 179-191 ◽  
Author(s):  
Jon S. Larsen ◽  
Ilmar F. Santos ◽  
Sebastian von Osmanski
Keyword(s):  
Foil Bearings ◽  
Rigid Rotors
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