scholarly journals Blade Excitation by Elliptical Whirling in Viscous-Damped Jet Engines

1980 ◽  
Author(s):  
Nicholas Klompas
Keyword(s):  
Experimental Verification ◽  
Linear Analysis ◽  
Squeeze Film ◽  
Jet Engines ◽  
Bladed Disks ◽  
Nonlinear Characteristics ◽  
Jet Engine ◽  
Squeeze Film Dampers

An extension of the author’s earlier method of analyzing multi-shaft jet engine dynamics accounting for flexibility of bladed disks is outlined to calculate the first whirl harmonic for given nonlinear characteristics of squeeze-film dampers. A second whirl harmonic, of which experimental verification is found in Campbell’s paper of 1924, is shown induced by orbit ellipticity. The possibility that this harmonic, especially due to backward whirling, may be a source of blade excitation at higher frequencies than currently recognized from linear analysis is discussed by relating some engine experience.

Blade Excitation by Elliptical Whirling in Viscous-Damped Jet Engines

1981 ◽  
Vol 103 (2) ◽  
pp. 326-330
Author(s):  
N. Klompas
Keyword(s):  
Experimental Verification ◽  
Linear Analysis ◽  
Squeeze Film ◽  
Jet Engines ◽  
Bladed Disks ◽  
Nonlinear Characteristics ◽  
Jet Engine ◽  
Squeeze Film Dampers

An extension of the author’s earlier method of analyzing multi-shaft jet engine dynamics accounting for flexibility of bladed disks is outlined to calculate the first whirl harmonic for given nonlinear characteristics of squeeze-film dampers. A second whirl harmonic, of which experimental verification is found in Campbell’s paper of 1924, is shown induced by orbit ellipticity. The possibility that this harmonic, especially due to backward whirling, may be a source of blade excitation at higher frequencies than currently recognized from linear analysis is discussed by relating some engine experience.

scholarly journals Effect of Temperature and Electric Field on the Damping and Stiffness Characteristics of ER Fluid Short Squeeze Film Dampers

2013 ◽  
Vol 2013 ◽  
pp. 1-10
Author(s):  
H. P. Jagadish ◽  
L. Ravikumar
Keyword(s):  
Electric Field ◽  
Strain Rate ◽  
Effect Of Temperature ◽  
Squeeze Film ◽  
Shear Strain Rate ◽  
Jet Engine ◽  
Squeeze Film Dampers ◽  
Stiffness And Damping ◽  
Rotor Dynamic ◽  
Er Fluid

Squeeze film dampers are novel rotor dynamic devices used to alleviate small amplitude, large force vibrations and are used in conjunction with antifriction bearings in aircraft jet engine bearings to provide external damping as these possess very little inherent damping. Electrorheological (ER) fluids are controllable fluids in which the rheological properties of the fluid, particularly viscosity, can be controlled in accordance with the requirements of the rotor dynamic system by controlling the intensity of the applied electric field and this property can be utilized in squeeze film dampers, to provide variable stiffness and damping at a particular excitation frequency. The paper investigates the effect of temperature and electric field on the apparent viscosity and dynamic (stiffness and damping characteristics) of ER fluid (suspension of diatomite in transformer oil) using the available literature. These characteristics increase with the field as the viscosity increases with the field. However, these characteristics decrease with increase in temperature and shear strain rate as the viscosity of the fluid decreases with temperature and shear strain rate. The temperature is an important parameter as the aircraft jet engine rotors are located in a zone of high temperature gradients and the damper fluid is susceptible to large variations in temperature.

Analysis of Hydrostatic Journal Bearings With End Seals

1992 ◽  
Vol 114 (4) ◽  
pp. 802-811 ◽  
Author(s):  
L. A. San Andres
Keyword(s):  
Journal Bearings ◽  
Squeeze Film ◽  
Dynamic Force ◽  
Jet Engines ◽  
Fluid Inertia ◽  
Active Device ◽  
Typical Application ◽  
Liquid Compressibility ◽  
Squeeze Film Dampers ◽  
Direct Stiffness

An approximate analysis for the pressure field and dynamic force coefficients in turbulent flow, centered hydrostatic journal bearings (HJBs) with fluid inertia and liquid compressibility effects is presented. Results from the analysis show that HJBs with end seals have increased damping, better dynamic stability characteristics, as well as lower flow rates, than conventional HJBs. However, hydrostatic (direct) stiffness may be lost if excessively tight end seals are used. End seals are shown to compensate for the effect of liquid compressibility within the recess volume, and prescribe a net reduction in the whirl frequency ratio for hybrid operation. Hydrostatic squeeze film dampers (HSFD) with end seals are shown to be a viable alternative in applications where a tight control of the bearing leakage is important such as in jet-engines. Furthermore, HSFDs with end seals could be used as an active device to control the available damping in a typical application.

Imbalance Response of a Rotor Supported on Open-Ends Integral Squeeze Film Dampers

1998 ◽  
Author(s):  
Oscar de Santiago ◽  
Luis San Andrés ◽  
Juan Oliveras
Keyword(s):  
Impact Load ◽  
Element Model ◽  
Squeeze Film ◽  
Jet Engines ◽  
Structural Damping ◽  
Equivalent Stiffness ◽  
Damping Coefficients ◽  
Squeeze Film Dampers ◽  
Vibration Attenuation ◽  
Lubricant Viscosity

Rotor vibration attenuation and structural components isolation in jet engines are achieved with squeeze film dampers, many of them supported on long elastic squirrel cages. Integral squeeze film dampers (ISFDs) are comprised of arcuate pads and wire-EDM webs rendering a compact viscoelastic support. An experimental study is conducted to evaluate the effectiveness of ISFDs in attenuating the imbalance response of a massive test rotor. Measurements of the damper structural stiffness and rotor natural frequencies are detailed. Impact tests on the test rotor supported on its dampers reveal the supporting structure to be very flexible, thus requiring the experimental evaluation of an equivalent stiffness for the damper and supports system. System damping coefficients extracted from impact load excitations vary with the lubricant viscosity and include a significant structural damping from the bearing supports. Rotor coast-down tests demonstrate the ISFDs to damp well the rotor response with peak vibration amplitude proportional (linear) to the imbalance. Viscous damping coefficients estimated from the amplitude response at the critical speeds agree reasonably well with predictions from a full-film, finite element model.

Imbalance Response of a Rotor Supported on Open-Ends Integral Squeeze Film Dampers

1999 ◽  
Vol 121 (4) ◽  
pp. 718-724 ◽  
Author(s):  
O. de Santiago ◽  
L. San Andre´s ◽  
J. Oliveras
Keyword(s):  
Impact Load ◽  
Element Model ◽  
Squeeze Film ◽  
Jet Engines ◽  
Structural Damping ◽  
Equivalent Stiffness ◽  
Damping Coefficients ◽  
Squeeze Film Dampers ◽  
Vibration Attenuation ◽  
Lubricant Viscosity

Rotor vibration attenuation and structural components isolation in jet engines are achieved with squeeze film dampers, many of them supported on long elastic squirrel cages. Integral squeeze film dampers (ISFDs) are comprised of arcuate pads and wire-EDM webs rendering a compact viscoelastic support. An experimental study is conducted to evaluate the effectiveness of ISFDs in attenuating the imbalance response of a massive test rotor. Measurements of the damper structural stiffness and rotor natural frequencies are detailed. Impact tests on the test rotor supported on its dampers reveal the supporting structure to be very flexible, thus requiring the experimental evaluation of an equivalent stiffness for the damper and supports system. System damping coefficients extracted from impact load excitations vary with the lubricant viscosity and include a significant structural damping from the bearing supports. Rotor coast-down tests demonstrate the ISFDs to damp well the rotor response with peak vibration amplitude proportional (linear) to the imbalance. Viscous damping coefficients estimated from the amplitude response at the critical speeds agree reasonably well with predictions from a full-film, finite element model.

Dynamic Response of a Rotor-Integral Squeeze Film Damper to Couple Imbalances

2000 ◽  
Author(s):  
Oscar De Santiago ◽  
Luis San Andrés
Keyword(s):  
High Speed ◽  
High Performance ◽  
Effective Means ◽  
Current Trend ◽  
Flexible Structures ◽  
Squeeze Film ◽  
Damping Capacity ◽  
Jet Engines ◽  
Squeeze Film Dampers ◽  
Dissipation Elements

Squeeze film dampers (SFDs) are used in high speed rotating machinery to reduce rotor vibration amplitudes and to isolate transmitted loads through the bearing support structures. SFDs are also effective means to ameliorate destructive subsynchronous vibrations excited by hydrodynamic bearings, seals, impellers and other unknown sources. Modern jet engines demand lighter and flexible structures with compact components to obtain the largest power to weight ratios. This current trend makes evident rotordynamic phenomena that must be adequately addressed by dissipation elements such as SFDs. Integral squeeze film dampers (ISFDs) incorporating built in elastic supports are of reduced weight and length, offer accuracy of positioning, and a split segment construction allowing easier assembly, inspection and retrofit. Yet ISFDs require of extensive experimentation to verify their dynamic forced performance and to prove their reliability for applications on high performance turbomachinery. Measurements of the synchronous response of a test rotor supported on ISFDs and due to couple-imbalances are hereby presented. Masses inserted at two axial planes in the rotor and out of phase by 180° excite the second (conical) mode of vibration of the test rotor. Peak rotor responses at the second critical speeds, vertical and horizontal, allow the determination of amplification factors from which system damping coefficients for the rotor conical motions are extracted. The measurements verify the damping capacity of ISFDs to reduce (conical mode) rotor vibrations.

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.

Determination of Damping Coefficient of a Bump Foil Squeeze Film Damper

2017 ◽  
Vol 8 (4) ◽  
Author(s):  
G. Saravanakumar ◽  
L. Ravikumar ◽  
R. Yogaraju ◽  
C. Shravankumar ◽  
V. Arunkumar
Keyword(s):  
Dynamic Characteristics ◽  
High Speed ◽  
Research Work ◽  
Squeeze Film ◽  
Jet Engines ◽  
Squeeze Film Damper ◽  
Squeeze Film Dampers ◽  
Magneto Rheological ◽  
Temperature Dynamic

The present investigation is aiming to get better squeeze film dampers which are normally used in high speed jet engines to minimize small amplitude large force vibrations. The investigation was started with squeeze film dampers employing conventional lubricating oils. Magneto rheological fluids are then used to enhance the viscosity characteristics of the fluid under the influence of magnetic fields in order to improve the damper performances. It is observed that the dynamic characteristics of the damper with magneto rheological fluids are enhanced. Further to improve the damper performance, few modifications in the damper assembly are carried out in this research work. A good amount of reduction in the amplitude of vibrations is observed in these modified squeeze film dampers coupled with magneto rheological fluids. This research work discusses dual and triple clearance squeeze film dampers and bump foil squeeze film damper, also subjected to variation in temperature. Dynamic characteristics are found to be decreasing as the viscosity of the fluid decreases with rise in temperature of the fluid.

Practical Bypass Mixing Systems for Fan Jet Aero Engines

1966 ◽  
Vol 17 (2) ◽  
pp. 141-160 ◽  
Author(s):  
T. H. Frost
Keyword(s):  
Gas Turbines ◽  
Minimum Weight ◽  
Jet Engines ◽  
Metal Interface ◽  
Combustion Chambers ◽  
Propulsion Systems ◽  
Jet Engine ◽  
Aero Engines ◽  
Corrugated Metal ◽  
Constant Static Pressure

SummaryMixing systems have many applications in gas turbines and aircraft jet propulsion, e.g. mixing zones in combustion chambers, ejectors for jet lift thrust augmentors and supersonic propulsion systems. A further application similar to that of combustion chamber mixing is that of mixing the cold and hot exhausts of a bypass jet engine. These are both characterised by mixing at constant static pressure and approximately constant total pressure as opposed to the more general case of unequal pressures in ejector systems (Fig. 1).The exhaust mixing process as used in Rolls-Royce bypass jet engines, e.g. Spey and Conway, enables the potential of the bypass principle, in terms of minimum weight and fuel consumption, to be exploited by a simple practical device.This is achieved by mixing the two streams in a common duct of fairly short dimensions with a corrugated metal interface on the inlet side. The consideration of these practical systems forms the main topic of this paper.

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