Dynamic Response and Stability of Pressurized Gas Squeeze-Film Dampers

1998 ◽  
Vol 120 (1) ◽  
pp. 306-311
Author(s):  
N. K. Arakere ◽  
B. C. Ravichandar
Keyword(s):  
High Temperature ◽  
Gas Flow ◽  
Squeeze Film ◽  
Orifice Diameter ◽  
Oil Lubrication ◽  
Damping Force ◽  
Circular Orbits ◽  
Foil Bearings ◽  
Flexible Rotors ◽  
Squeeze Film Dampers

Compressible squeeze films, an important and interesting area in gas lubrication, have been relatively neglected in recent times. Aircraft engines are being designed with light weight flexible rotors operating at high speeds and temperatures that may eventually eliminate the use of oil lubrication. A gas or air SFD might be a viable alternative to a conventional oil damper, in high temperature applications that preclude the use of oil lubrication. Oil squeeze-film dampers currently being used for rotordynamic control will not be viable at temperatures above 350°F, due to limitations on lubricant oil temperature. A good example of gas SFD application is in conjunction with high temperature gas lubricated foil bearings, which inherently have low damping. This paper presents an analysis of pressurized air dampers, similar to a hydrostatic gas bearing. Pressurized air is supplied through a series of orifices in the bearing midplane. Airflows through the orifices and the resulting pressure forces are calculated using a simple gas-flow model, as in orifice compensated hydrostatic bearings. A small perturbation analysis of the shaft center yields the stiffness and damping coefficients, for centered circular orbits. Damping characteristics are studied for a range of parameters such as supply pressure, orifice diameter, pocket volume, orbit size, number of orifices and shaft speed. Results show that maximum damping forces are generated for near choking flow conditions. The damping coefficient becomes negligible at frequencies above 350 Hz. For damping force to be present, the gas pressurization has to exert a force on the rotor opposing the instantaneous velocity, or, 90 degrees out of phase with displacement. Linear stability of unbalanced dampers undergoing centered circular orbits, is also investigated, in view of their relevance to rotordynamics. Damper design curves are presented for various parameters.

Dynamic Response and Stability of Pressurized Gas Squeeze-Film Dampers

1995 ◽  
Author(s):  
Nagaraj K. Arakere ◽  
B. C. Ravichandar
Keyword(s):  
High Temperature ◽  
Gas Flow ◽  
Squeeze Film ◽  
Orifice Diameter ◽  
Oil Lubrication ◽  
Damping Force ◽  
Foil Bearings ◽  
Flexible Rotors ◽  
Squeeze Film Dampers ◽  
Damper Design

Abstract Compressible squeeze films, an important and interesting area in gas lubrication, have been relatively neglected in recent times. Aircraft engines are being designed with light weight flexible rotors operating at high speeds and temperatures that may eventually eliminate the use of oil lubrication. A gas or air SFD might be a viable alternative to a conventional oil damper, in high temperature applications that preclude the use of oil lubrication. Oil squeeze-film dampers currently being used for rotordynamic control will not be viable at temperatures above 350 °F, due to limitations on lubricant oil temperature. Gas SFD’s are well suited for use in high temperature gas lubricated foil bearings. This paper presents an analysis of pressurized air dampers, similar to a hydrostatic gas bearing. Pressurized air is supplied through a series of orifices in the bearing midplane. Air flows through the orifices and the resulting pressure forces are calculated using a simple gas-flow model, as in orifice compensated hydrostatic bearings. A small perturbation analysis of the shaft center yields the stiffness and damping coefficients, for centered circular motions. Damping characteristics are studied for a range of parameters such as supply pressure, orifice diameter, pocket volume, orbit size, number of orifices and shaft speed. Results show that maximum damping forces are generated for near choking flow conditions. The damping force becomes negligible at frequencies above 350 Hz. For damping force to be present, the gas pressurization has to exert a force on the rotor opposing the instantaneous velocity, or, 90 degrees out of phase with displacement Linear stability of unbalanced dampers undergoing centered circular orbits, is also investigated, in view of their relevance to rotordynamics. Damper design curves are presented for various parameters.

Investigations of Transient Oscillations of Rotors Supported by Magnetorheological Squeeze Film Dampers Using Bilinear Material to Model the Lubricant

2016 ◽  
Vol 821 ◽  
pp. 309-316
Author(s):  
Jaroslav Zapoměl ◽  
Jan Kozánek ◽  
Petr Ferfecki
Keyword(s):  
Squeeze Film ◽  
Lateral Vibration ◽  
Technological Solution ◽  
Damping Force ◽  
Motion Equations ◽  
Damping Effect ◽  
Squeeze Film Dampers ◽  
Nonlinear Character ◽  
Operating Regimes ◽  
Transient Oscillations

Unbalance of rotors is one of the principal causes of their lateral vibration. A technological solution frequently used to its suppression consists in placing damping devices to the rotor supports. To achieve their optimum performance their damping effect must be controllable. This is offered by squeeze film dampers utilizing the magnetorheological phenomenon to control the damping force. In mathematical models magnetorheological oils are usually represented by Bingham or Herschel-Bulkley theoretical materials. Here the magnetorheological oil is modeled by bilinear material with the yielding shear stress depending on magnetic induction. Its flow curve is continuous which contributes to reducing nonlinear character of the motion equations. The new mathematical model was applied to investigate several operating regimes of rotating machines.

Use of the Harmonic Balance Method for Flexible Aircraft Engine Rotors With Nonlinear Squeeze Film Dampers

2014 ◽  
Author(s):  
Feng He ◽  
Paul Allaire ◽  
Timothy Dimond
Keyword(s):  
Harmonic Balance ◽  
Harmonic Balance Method ◽  
Aircraft Engine ◽  
Balance Method ◽  
Squeeze Film ◽  
Spring Stiffness ◽  
Squeeze Film Damper ◽  
Flexible Rotors ◽  
Squeeze Film Dampers ◽  
Nonlinear Transient

Squeeze film dampers in flexible rotors such as those in compressors, steam turbines, aircraft engines and other rotating machines are often modeled as linear devices. This linearization is valid only for a specified orbit where appropriate equivalent stiffness and damping coefficients can be found. However, squeeze film dampers are inherently nonlinear devices which complicates the analysis. This paper develops the harmonic balance method with a direct force model of the SFDs. This model is used for flexible rotors with squeeze film dampers where the rotor is treated as linear and the squeeze film damper is treated as nonlinear. The predictor-corrector method is employed to obtain the system forced response in the frequency domain after separating the nonlinear components from the linear components of the equations of motion. This approach is much more efficient than conventional full nonlinear transient analysis. The application considered in this paper is the low pressure (LP) compressor of an aircraft engine. The LP compressor rotor has two roller bearings with squeeze film dampers and one ball bearing without a squeeze film damper. Orbits at the fan end dampers and the turbine end dampers for both the harmonic balance and nonlinear transient modeling are compared for accuracy and calculation time. The HB method is shown to be 5 to 12 times faster computationally for similar results. Fast Fourier transform results were obtained for various shaft operating speeds. Results were also obtained for the unbalance response at different locations with gravity loading. Finally, unbalance response of the rotor with varying centering spring stiffness values were obtained. The results show that the centering spring stiffness for the turbine end damper is less sensitive than the fan end damper.

Jørgen Lund: A Perspective on His Contributions to Modern Rotor Bearing Dynamics

2003 ◽  
Vol 125 (4) ◽  
pp. 434-440
Author(s):  
Anthony J. Smalley
Keyword(s):  
Knowledge Base ◽  
Modal Testing ◽  
Squeeze Film ◽  
Gas Bearings ◽  
Road Map ◽  
Flexible Rotors ◽  
Squeeze Film Dampers ◽  
Rotor Bearing ◽  
Bearing Dynamics ◽  
Rotor Balancing

This paper presents a perspective on the work of Dr. J. W. Lund, in the field of rotor-bearing dynamics. It traces his most influential work in published journals, software, data published in various manuals, government reports, and course notes. It addresses his work in oil bearings, gas bearings, unbalance response of flexible rotors, stability of flexible rotors, squeeze-film dampers, rotor balancing, and modal testing of rotors. It provides a road map for those who would revisit the knowledge base. It shows how Dr. Lund’s work has permeated the practice of today’s suppliers and users of turbomachinery, and industry consultants.

Experimental Pressures and Film Forces in a Squeeze Film Damper

1993 ◽  
Vol 115 (1) ◽  
pp. 134-140 ◽  
Author(s):  
G. L. Arauz ◽  
L. A. San Andres
Keyword(s):  
Tangential Force ◽  
Radial Force ◽  
Squeeze Film ◽  
Radial Clearance ◽  
Fluid Inertia ◽  
Damping Force ◽  
Inertia Effects ◽  
Squeeze Film Dampers ◽  
Tangential Forces ◽  
Lubricant Viscosity

The effect of whirl frequency and lubricant viscosity on the dynamic pressures and force response of an open end and a partially sealed squeeze film dampers (SFD) with a radial clearance of 0.38 mm is determined experimentally. The experiments are carried out in a damper test rig executing circular centered orbits and for whirl frequencies ranging from 33 to 83 Hz. The experimental results show that the sealed SFD configuration produces larger tangential forces than the open end SFD. The tangential (damping) force increases linearly with increasing whirl frequency. For this radial clearance fluid inertia effects in the damper are found to be negligible since the squeeze film Reynolds number is less than 1.20. Cavitation was observed in both damper configurations at high frequencies and high lubricant viscosities. This condition limited the rate of increment of the damping (tangential) force with increasing frequency and reduced the radial force when lubricant viscosity increased.

Application of the Magnetorheological Squeeze Film Dampers for Reducing Energy Losses in Supports of Rotors of Rotating Machines

2017 ◽  
Author(s):  
Jaroslav Zapoměl ◽  
Petr Ferfecki
Keyword(s):  
Mathematical Model ◽  
Dynamical Analysis ◽  
Squeeze Film ◽  
Energy Losses ◽  
Damping Force ◽  
Squeeze Film Damper ◽  
Damping Effect ◽  
Wide Range ◽  
Squeeze Film Dampers ◽  
Computational Procedures

Unbalance of rotating parts is the main source of excitation of lateral oscillations of rotors, of increase of time varying forces transmitted to the rotor stationary part, and of energy losses generated in the support elements. The technological solution, which makes it possible to reduce these undesirable effects, consists in adding damping devices to the rotor supports. A simple dynamical analysis shows that to achieve their optimum performance their damping effect must be adaptable to the current operating speed. This is enabled by magnetorheological squeeze film dampers, the damping effect of which is controlled by the change of magnetic flux passing through the lubricating layer. The developed mathematical model of the magnetorheological squeeze film damper is based on assumptions of the classical theory of lubrication and on representing the magnetorheological oil by a bilinear material. The results of the carried out computational simulations show that the appropriate control of the damping force makes it possible to minimize the energy losses in a wide range of operating speeds. The development of a new mathematical model of the magnetorheological squeeze film damper, the extension of computational procedures, in which this model has been implemented, the confirmation that the magnetorheological dampers make it possible to reduce energy losses in the rotor supports, and learning more on influence of controllable dampers on behavior of rotor systems are the principal contributions of the presented paper. The carried out research highlights the possibility of reducing the energy losses by means of employing magnetorheological squeeze film dampers, which represents a new field of their prospective application.

A Computational Investigation of the Steady State Vibrations of Unbalanced Flexibly Supported Rigid Rotors Damped by Short Magnetorheological Squeeze Film Dampers

2013 ◽  
Vol 135 (6) ◽  
Author(s):  
Jaroslav Zapoměl ◽  
Petr Ferfecki ◽  
Paola Forte
Keyword(s):  
Steady State ◽  
Equations Of Motion ◽  
Dynamical Behavior ◽  
Steady State Solution ◽  
Squeeze Film ◽  
Damping Force ◽  
Lateral Vibrations ◽  
Lubricating Layer ◽  
Squeeze Film Dampers ◽  
Rigid Rotors

Unbalance is the principal cause of excitation of lateral vibrations of rotors and generation of the forces transmitted through the rotor supports to the foundations. These effects can be significantly reduced if damping devices are added to the constraint elements. To achieve their optimum performance, their damping effect must be controllable. The possibility of controlling the damping force is offered by magnetorheological squeeze film dampers. This article presents an original investigation of the dynamical behavior of a rigid flexibly supported rotor loaded by its unbalance and equipped with two short magnetorheological squeeze film dampers. In the computational model, the rotor is considered as absolutely rigid and the dampers are represented by force couplings. The pressure distribution in the lubricating layer is governed by a modified Reynolds equation adapted for Bingham material, which is used to model the magnetorheological fluid. To obtain the steady state solution of the equations of motion, a collocation method is employed. Stability of the periodic vibrations is evaluated by means of the Floquet theory. The proposed approach to study the behavior of rigid rotors damped by semi-active squeeze film magnetorheological dampers and the developed efficient computational methods to calculate the system steady state response and to evaluate its stability represent new contributions of this article.

scholarly journals Imbalance Response and Damping Force Coefficients of a Rotor Supported on End Sealed Integral Squeeze Film Dampers

1999 ◽  
Author(s):  
Oscar C. De Santiago ◽  
Luis A. San Andrés
Keyword(s):  
High Performance ◽  
Effective Means ◽  
Squeeze Film ◽  
Damping Force ◽  
Damping Coefficients ◽  
Squeeze Film Dampers ◽  
Flow Through ◽  
Structural Isolation ◽  
The Impact ◽  
Severe Penalty

To this date, squeeze film dampers (SFDs) are effective means to reduce vibrations and provide structural isolation in high performance aeroengine systems. Integral squeeze film dampers (ISFDs) offer distinct advantages such as reduced overall weight, accuracy of positioning, and a split segment construction allowing easier assembly, inspection and retrofit. An experimental study is conducted to evaluate the effectiveness of integral dampers in attenuating the imbalance response of a massive test rotor. Damping coefficients for end sealed dampers are identified from the peak rotor responses due to imbalances while passing through the fundamental critical speeds. Impact response measurements at null rotor speed are also conducted to identify system damping coefficients for increasing values of the lubricant temperature. The impact tests and imbalance response measurements demonstrate that end gap seals increase effectively the ISFD viscous damping coefficients and without a severe penalty in the flow through the dampers. The experiments further demonstrate that the amplitudes of rotor synchronous response are proportional to the imbalance displacements without subsynchronous frequencies or (nonlinear) jump responses.

Orbit-Based Identification of Damping Coefficients for a Rotor Mounted on Off-Centered Squeeze Film Dampers and Including Support Flexibility

2000 ◽  
Author(s):  
Sergio Diaz ◽  
Luis San Andrés
Keyword(s):  
Least Square ◽  
Squeeze Film ◽  
Dramatic Improvement ◽  
Jet Engines ◽  
Damping Force ◽  
Force Coefficients ◽  
Damping Coefficients ◽  
Process Gas ◽  
Squeeze Film Dampers ◽  
Rotor Bearing

Squeeze film dampers (SFDs) provide structural isolation and energy dissipation in jet engines and process gas compressors. The determination of linearized damping force coefficients to allow the use of well-developed linear techniques is of importance in the design and reliability analysis of rotor-bearing systems dynamic response and stability. Two parameter identification techniques to estimate the linearized viscous damping coefficients of a rotor-bearing system based on the measurement of rotor displacements are presented. The first method applies a least-square curve fitting to the damping force, while the second determines the elliptic orbit that best approximates the actual one. The filtered orbit method is applied to identify the damping force coefficients from measurements of the synchronous response of a test rotor mounted on off-centered SFDs. The identified system damping coefficients (direct and cross-coupled) are found to be independent of the imbalance magnitude and shaft speed, in spite of the large amplitude rotor motions within the dampers’ clearances. A modification of the method to include the damper bearing support flexibility shows a dramatic improvement on the predicted rotor response and more reliable force coefficients.

SCIENTIFIC AND ENGINEERING PRINCIPLES OF EFFICIENT FUEL USE AND ENVIRONMENTALLY FRIENDLY GAS COMBUSTION IN STOVE PLATES. PART 1. MODERN STATE-OF-THE-ART AND DIRECTIONS FOR IMPROVEMENT THE GAS BURNING IN DOMESTIC GAS COOKERS

2017 ◽  
pp. 3-18 ◽  
Author(s):  
B.S. Soroka ◽  
V.V. Horupa
Keyword(s):  
Natural Gas ◽  
Flow Rate ◽  
Gas Flow ◽  
Renewable Energy Sources ◽  
Combustion Process ◽  
Orifice Diameter ◽  
Firing Process ◽  
Gas Flow Rate ◽  
Gas Combustion ◽  
Gas Stoves

Natural gas NG consumption in industry and energy of Ukraine, in recent years falls down as a result of the crisis in the country’s economy, to a certain extent due to the introduction of renewable energy sources along with alternative technologies, while in the utility sector the consumption of fuel gas flow rate enhancing because of an increase the number of consumers. The natural gas is mostly using by domestic purpose for heating of premises and for cooking. These items of the gas utilization in Ukraine are already exceeding the NG consumption in industry. Cooking is proceeding directly in the living quarters, those usually do not meet the requirements of the Ukrainian norms DBN for the ventilation procedures. NG use in household gas stoves is of great importance from the standpoint of controlling the emissions of harmful components of combustion products along with maintenance the satisfactory energy efficiency characteristics of NG using. The main environment pollutants when burning the natural gas in gas stoves are including the nitrogen oxides NOx (to a greater extent — highly toxic NO2 component), carbon oxide CO, formaldehyde CH2O as well as hydrocarbons (unburned UHC and polyaromatic PAH). An overview of environmental documents to control CO and NOx emissions in comparison with the proper norms by USA, EU, Russian Federation, Australia and China, has been completed. The modern designs of the burners for gas stoves are considered along with defining the main characteristics: heat power, the natural gas flow rate, diameter of gas orifice, diameter and spacing the firing openings and other parameters. The modern physical and chemical principles of gas combustion by means of atmospheric ejection burners of gas cookers have been analyzed from the standpoints of combustion process stabilization and of ensuring the stability of flares. Among the factors of the firing process destabilization within the framework of analysis above mentioned, the following forms of unstable combustion/flame unstabilities have been considered: flashback, blow out or flame lifting, and the appearance of flame yellow tips. Bibl. 37, Fig. 11, Tab. 7.

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