scholarly journals Imbalance Response of a Test Rotor Supported on Squeeze Film Dampers

1997 ◽  
Author(s):  
Luis San Andrés ◽  
Daniel Lubell
Keyword(s):  
Chaotic Behavior ◽  
Theoretical Models ◽  
Forced Response ◽  
Analytical Models ◽  
Squeeze Film ◽  
Test Rig ◽  
Critical Speeds ◽  
Highly Nonlinear ◽  
Squeeze Film Dampers ◽  
Elastomeric Seals

Squeeze film dampers (SFDs) provide vibration attenuation and structural isolation to aircraft gas turbine engines which must be able to tolerate larger imbalances while operating above one or more critical speeds. Rotor-bearing-SFD systems are regarded in theory as highly nonlinear, showing jump-phenomena and even chaotic behavior for sufficiently large levels of rotor imbalance. Yet, few experimental results of practical value have verified the analytical predictions. A test rig for measurement of the dynamic forced response of a three-disk rotor (45 kg) supported on two cylindrical SFDs is described. The major objective is to provide a reliable data base to validate and enhance SFD design practice and to allow a direct comparison with analytical models. The open-ends SFD are supported by four-bar centering structures each with a stiffness of 3.5 MN/m. Measured synchronous responses to 9,000 rpm due to various imbalances show the rotor-SFD system to be well damped with amplification factors between 1.6 and 2.1 while traversing cylindrical and conical modes critical speeds. The rotor amplitudes of motion are found to be proportional to the imbalances for the first mode of vibration, and the damping coefficients extracted compare reasonably well to predictions based on the full-film open-ends SFD. Tight lip (elastomeric) seals contribute greatly to the overall damping of the test rig. Measured dynamic pressures at the squeeze film lands are well above ambient values with no indication of lubricant dynamic cavitation as simple theoretical models dictate. The measurements show absence of non-linear behavior of the rotor-SFD apparatus for the range of imbalances tested. • The research program is a joint effort funded by the National Science Foundation (NSF) and the TAMU Turbomachinery Research Consortium (TRC).

scholarly journals Imbalance Response of a Test Rotor Supported on Squeeze Film Dampers

1998 ◽  
Vol 120 (2) ◽  
pp. 397-404 ◽  
Author(s):  
L. San Andre´s ◽  
D. Lubell
Keyword(s):  
Chaotic Behavior ◽  
Nonlinear Behavior ◽  
Theoretical Models ◽  
Forced Response ◽  
Analytical Models ◽  
Squeeze Film ◽  
Test Rig ◽  
Critical Speeds ◽  
Highly Nonlinear ◽  
Squeeze Film Dampers

Squeeze film dampers (SFDs) provide vibration attenuation and structural isolation to aircraft gas turbine engines which must be able to tolerate larger imbalances while operating above one or more critical speeds. Rotor-bearing-SFD systems are regarded in theory as highly nonlinear, showing jump phenomena and even chaotic behavior for sufficiently large levels of rotor imbalance. Yet, few experimental results of practical value have verified the analytical predictions. A test rig for measurement of the dynamic forced response of a three-disk rotor (45 kg) supported on two cylindrical SFDs is described. The major objective is to provide a reliable data base to validate and enhance SFD design practice and to allow a direct comparison with analytical models. The open-ends SFD are supported by four-bar centering structures, each with a stiffness of 3.5 MN/m. Measured synchronous responses to 9000 rpm due to various imbalances show the rotor-SFD system to be well damped with amplification factors between 1.6 and 2.1 while traversing cylindrical and conical modes critical speeds. The rotor amplitudes of motion are found to be proportional to the imbalances for the first mode of vibration, and the damping coefficients extracted compare reasonably well to predictions based on the full-film, open-ends SFD. Tight lip (elastomeric) seals contribute greatly to the overall damping of the test rig. Measured dynamic pressures at the squeeze film lands are well above ambient values with no indication of lubricant dynamic cavitation as simple theoretical models dictate. The measurements show absence of nonlinear behavior of the rotor-SFD apparatus for the range of imbalances tested.

Nonlinear Analysis of Rotor-Bearing Systems Using Component Mode Synthesis

1983 ◽  
Vol 105 (3) ◽  
pp. 606-614 ◽  
Author(s):  
H. D. Nelson ◽  
W. L. Meacham ◽  
D. P. Fleming ◽  
A. F. Kascak
Keyword(s):  
Forced Response ◽  
Component Mode Synthesis ◽  
Squeeze Film ◽  
System Response ◽  
Reduced Order ◽  
Squeeze Film Dampers ◽  
Rotor Bearing ◽  
System Equations ◽  
Transient System ◽  
Blade Loss

The method of component mode synthesis is developed to determine the forced response of nonlinear, multishaft, rotor-bearing systems. The formulation allows for simulation of system response due to blade loss, distributed unbalance, base shock, maneuver loads, and specified fixed frame forces. The motion of each rotating component of the system is described by superposing constraint modes associated with boundary coordinates and constrained precessional modes associated with internal coordinates. The precessional modes are truncated for each component and the reduced component equations are assembled with the nonlinear supports and interconnections to form a set of nonlinear system equations of reduced order. These equations are then numerically integrated to obtain the system response. A computer program, which is presently restricted to single shaft systems has been written and results are presented for transient system response associated with blade loss dynamics, with squeeze film dampers, and with interference rubs.

scholarly journals Dynamic Behavior of Geared Rotors

1997 ◽  
Author(s):  
T. N. Shiau ◽  
J. S. Rao ◽  
J. R. Chang ◽  
Siu-Tong Choi
Keyword(s):  
Dynamic Behavior ◽  
Chaotic Behavior ◽  
Squeeze Film ◽  
Rotor Systems ◽  
Lateral Vibrations ◽  
Squeeze Film Dampers ◽  
Torsional Excitation ◽  
Route To Chaos

This paper is concerned with the dynamic behavior of geared rotor systems supported by squeeze film dampers, wherein coupled bending torsion vibrations occur. Considering the imbalance forces and gravity, it is shown that geared rotors exhibit chaotic behavior due to non linearity of damper forces. The route to chaos in such systems is established. In geared rotor systems, it is shown that torsional excitation can induce lateral vibrations. It is shown that squeeze film dampers can suppress large amplitudes of whirl arising out of torsional excitation.

On the Experimental Dynamic Force Performance of a Squeeze Film Damper Supplied Through a Check Valve and Sealed With O-Rings

2021 ◽  
Author(s):  
Luis San Andrés ◽  
Bryan Rodríguez
Keyword(s):  
Dynamic Pressure ◽  
Excitation Frequency ◽  
Check Valve ◽  
Forced Response ◽  
Single Frequency ◽  
Squeeze Film ◽  
Dynamic Force ◽  
Viscous Damping ◽  
Test Rig ◽  
Force Coefficients

Abstract In rotor-bearing systems, squeeze film dampers (SFDs) assist to reduce vibration amplitudes while traversing a critical speed and also offer a means to suppress rotor instabilities. Along with an elastic support element, SFDs are effective means to isolate a rotor from its casing. O-rings (ORs), piston rings (PRs) and side plates as end seals reduce leakage and air ingestion while amplifying the viscous damping in configurations with limited physical space. ORs also add a centering stiffness and damping to a SFD. The paper presents experiments to quantify the dynamic forced response of an O-rings sealed ends SFD (OR-SFD) lubricated with ISO VG2 oil supplied at a low pressure (0.7 bar(g)). The damper is 127 mm in diameter (D), short in axial length L = 0.2D, and the film clearance c = 0.279 mm. The lubricant flows into the film land through a mechanical check valve and exits through a single port. Upstream of the check valve, a large plenum filled with oil serves to attenuate dynamic pressure disturbances. Multiple sets of single-frequency dynamic loads, 10 Hz to 120 Hz, produce circular centered orbits with amplitudes r = 0.1c, 0.15c and 0.2c. The experimental results identify the test rig structure, ORs and SFD force coefficients; namely stiffness (K), mass (M) and viscous damping (C). The ORs coefficients are frequency independent and show a sizeable direct stiffness, KOR ∼ 50% of the test rig structure stiffness, along with a quadrature stiffness, K0∼0.26 KOR, demonstrative of material damping. The lubricated system damping coefficient equals CL = (CSFD + COR); the ORs contributing 10% to the total. The experimental SFD damping and inertia coefficients are large in physical magnitude; CSFD slightly grows with orbit size whereas MSFD is relatively constant. The added mass (MSFD) is approximately four-fold the bearing cartridge mass; hence, the test rig natural frequency drops by ∼50% once lubricated. A computational physics model predicts force coefficients that are just 10% lower than those estimated from experiments. The amplitude of measured dynamic pressures upstream of the plenum increases with excitation frequency. Unsuspectedly, during dynamic load operation, the check valve did allow for lubricant backflow into the plenum. Post-tests verification demonstrates that, under static pressure conditions, the check valve does work since it allows fluid flow in just one direction.

Routes to Chaos in Squeeze-Film Dampers

2004 ◽  
Author(s):  
Jawaid I. Inayat-Hussain ◽  
Njuki W. Mureithi
Keyword(s):  
Period Doubling ◽  
Squeeze Film ◽  
Saddle Node Bifurcation ◽  
Chaotic Vibrations ◽  
Saddle Node ◽  
Highly Nonlinear ◽  
Squeeze Film Dampers ◽  
Route To Chaos ◽  
Type 3 ◽  
Period Doubling Bifurcations

This work reports on a numerical study undertaken to investigate the imbalance response of a rigid rotor supported by squeeze-film dampers. Two types of damper configurations were considered, namely, dampers without centering springs, and eccentrically operated dampers with centering springs. For a rotor fitted with squeeze-film dampers without centering springs, the study revealed the existence of three regimes of chaotic motion. The route to chaos in the first regime was attributed to a sequence of period-doubling bifurcations of the period-1 (synchronous) rotor response. A period-3 (one-third subharmonic) rotor whirl orbit, which was born from a saddle-node bifurcation, was found to co-exist with the chaotic attractor. The period-3 orbit was also observed to undergo a sequence of period-doubling bifurcations resulting in chaotic vibrations of the rotor. The route to chaos in the third regime of chaotic rotor response, which occurred immediately after the disappearance of the period-3 orbit due to a saddle-node bifurcation, was attributed to a possible boundary crisis. The transitions to chaotic vibrations in the rotor supported by eccentric squeeze-film dampers with centering springs were via the period-doubling cascade and type 3 intermittency routes. The type 3 intermittency transition to chaos was due to an inverse period-doubling bifurcation of the period-2 (one-half subharmonic) rotor response. The unbalance response of the squeeze-film-damper supported rotor presented in this work leads to unique non-synchronous and chaotic vibration signatures. The latter provide some useful insights into the design and development of fault diagnostic tools for rotating machinery that operate in highly nonlinear regimes.

Analysis and Experimental Investigation of the Stability of Intershaft Squeeze Film Dampers—Part 2: Control of Instability

1978 ◽  
Vol 100 (3) ◽  
pp. 558-562 ◽  
Author(s):  
D. H. Hibner ◽  
P. N. Bansal ◽  
D. F. Buono
Keyword(s):  
Experimental Investigation ◽  
Stability Analysis ◽  
Shear Deformation ◽  
System Stability ◽  
Squeeze Film ◽  
Viscous Damper ◽  
Test Rig ◽  
Squeeze Film Dampers ◽  
Stability Maps ◽  
The Stability

The results of an analytical and experimental investigation showing the existence of an intershaft viscous damper instability were presented in reference [1]. In the present investigation, a more comprehensive stability analysis is used to study the stability of the test rig which incorporates a modified intershaft bearing support. The analysis is applicable to large multi-mass, rotor-bearing systems and includes the effects of gyroscopic moments, shear deformation, bearing support flexibility, and damping. The results of the stability analysis are presented in the form of system stability maps which clearly indicate the effectiveness of the modification in improving the instability onset speed of the system. Also presented are the results of an experimental investigation which substantiate the analytical predictions.

Squeeze-Film Damper Predictions for Simulation of Aircraft Engine Rotordynamics

2004 ◽  
Author(s):  
Cyril Defaye ◽  
Franck Laurant ◽  
Philippe Carpentier ◽  
Mihai Arghir ◽  
Olivier Bonneau ◽  
...  
Keyword(s):  
Reynolds Equation ◽  
Aircraft Engine ◽  
Theoretical Work ◽  
Analytical Models ◽  
Squeeze Film ◽  
Design Parameters ◽  
Aircraft Engines ◽  
Predictive Tool ◽  
Squeeze Film Dampers ◽  
Inertia Forces

On aircraft engines, a common recurring problem is excessive vibration levels generated by unbalance. With rotors mounted on usual undamped ball bearings, an amount of damping is required to limit peak amplitudes at traversed critical speeds: a solution is to introduce external damping with squeeze-film dampers. Such dampers can be added with minor modifications of the rotor system design. This paper presents experimental and theoretical work in progress focused on the analysis of squeeze film dampers (SFD) based on serial aircraft engines design. Several squeeze-film geometries were tested to measure the influence of different design parameters as the fluid clearance and the groove feeding system. Next, a damper model based on the numerical solution of the Reynolds equation is correlated with the experimental data to obtain predictive global forces. It is shown that the theoretical model is a good predictive tool if it is correctly adjusted and if temporal inertia forces are negligible. The present damper model is further compared with analytical models taken from the literature which are obviously more appropriate to be used in whole engine rotordynamic analysis. The limits of the models are then underlined by comparisons with experimental results.

Frequency Dependancy of Dynamic Force Coefficients for Hermetic Squeeze Film Dampers Utilizing Fluid-Bounding Flexible Structures

2021 ◽  
Author(s):  
Bugra Ertas ◽  
Keith Gary
Keyword(s):  
Fluid Dynamics ◽  
Flexible Structures ◽  
Analytical Models ◽  
Squeeze Film ◽  
Dynamic Force ◽  
Design Modification ◽  
Frequency Dependency ◽  
Force Coefficients ◽  
Squeeze Film Dampers ◽  
Frequency Independent

Abstract The following paper focuses on the dynamic behavior of hermetic squeeze film dampers (HSFD) that utilize fluid-bounding flexible members as a part of the support structure. More specifically, the current paper advances an engineering design modification to the existing HSFD concept, which is aimed at rendering the dynamic force coefficients frequency independent. The paper builds on past HSFD testing and modeling approaches to develop higher fidelity analytical models, which are used to investigate different damper configurations while taking keen interest in the frequency dependency of force coefficients. The analytical study leverages commercially available finite element analysis (FEA) and computational fluid dynamics (CFD) software to conduct several fluid-structure-interaction (FSI) simulations of various damper architectures. In addition to the FSI analysis a more computationally efficient reduced order model (ROM) was developed, coupling structural flexibility with the fluid dynamics in the damper. Ultimately, these design tools were used to identify critical design features and configurations needed for constant linear frequency independent force coefficients. The results show a damper configuration with minimal frequency dependency of the stiffness and damping coefficients when incorporating pass through channels in combination with accumulator volumes. The paper also uses the improved design approach of the HSFD to put forth a notional integrated bearing design incorporating the new HSFD concept.

Imbalance Response of a Rotor Supported on Flexure Pivot Tilting Pad Journal Bearings in Series With Integral Squeeze Film Dampers

2001 ◽  
Author(s):  
Luis San Andrés ◽  
Oscar De Santiago
Keyword(s):  
Peak Amplitude ◽  
Squeeze Film ◽  
Critical Speeds ◽  
Rotor Imbalance ◽  
Squeeze Film Dampers ◽  
Tilting Pad ◽  
Rotor Bearing ◽  
In Series ◽  
Tilting Pad Bearings ◽  
Tilting Pad Journal Bearings

Measurements of the imbalance responses of a massive 45 kg rotor supported on series (flexure pivot) tilting pad bearings and integral squeeze film dampers (SFDs) are presented. The rotor-bearing configuration is of interest in compressor applications where often oil lubricated dampers are introduced in series with fluid film bearings to relocate critical speeds, enhance the overall system damping, and reduce the risks of rotordynamic instabilities due to seals and impellers, for example. Coast-down experiments from 9,000 rpm are conducted for increasing levels of rotor imbalance, and equivalent system damping coefficients identified from the peak amplitude of rotor response while traversing cylindrical mode critical speeds. The tests performed with locked (inactive) and active SFDs demonstrate the effectiveness of the flexible damped support in reducing the system critical speed and improving the overall rotor response with reduced transmitted forces to ground. The SFDs allow safe rotor operation with values of imbalance twice as large as the maximum sustained by the rotor supported on tilting pad bearings alone. The experiments reveal a linear relationship between the peak amplitude of vibration at the critical speeds and the imbalance displacement, even for rotor motions larger than 50% of the tilting pad bearing and damper clearances. The tests also show little cross-coupling effects with the shaft centerline moving along a nearly vertical path. The rotor-bearing system remained stable in the entire range of operation and without the appearance of subsynchronous vibration or non-linear damper jump response.

Experimental Performance of an Open Ends, Centrally Grooved, Squeeze Film Damper Operating With Large Amplitude Orbital Motions

2014 ◽  
Vol 137 (3) ◽  
Author(s):  
Luis San Andrés ◽  
Sung-Hwa Jeung
Keyword(s):  
Large Amplitude ◽  
Gas Turbines ◽  
Mechanical Energy ◽  
Forced Response ◽  
Dynamic Loads ◽  
Squeeze Film ◽  
Radial Clearance ◽  
Force Coefficients ◽  
Squeeze Film Dampers ◽  
Static Eccentricity

Aircraft engines customarily implement squeeze film dampers (SFDs) to dissipate mechanical energy caused by rotor vibration and to isolate the rotor from its structural frame. The paper presents experimental results for the dynamic forced performance of an open ends SFD operating with large amplitude whirl motions, centered and off-centered. The test rig comprises of an elastically supported bearing with a damper section, 127 mm in diameter, having two parallel film lands separated by a central groove. Each film land is 25.4 mm long with radial clearance c = 0.251 mm. The central groove, 12.7 mm long, has a depth of 9.5 mm (38c). An ISO VG 2 lubricant flows into the groove via three 2.5 mm orifices, 120 deg apart, and then passes through the film lands to exit at ambient condition. Two orthogonally placed shakers apply dynamic loads on the bearing to induce circular orbit motions with whirl frequency ranging from 10 Hz to 100 Hz. A static loader, 45 deg away from each shaker, pulls the bearing to a static eccentricity (es). Measurements of dynamic loads and the ensuing bearing displacements and accelerations, as well as the film and groove dynamic pressures, were obtained for eight orbit amplitudes (r = 0.08c to ∼0.71c) and under four static eccentricities (es = 0.0c to ∼0.76c). The experimental damping coefficients increase quickly as the bearing offset increases (es/c → 0.76) while remaining impervious to the amplitude of whirl orbit (r/c → 0.51). The inertia coefficients decrease rapidly as the orbit amplitude grows large, r > 0.51c, but increase with the static eccentricity. A comparison with test results obtained with an identical damper but having a smaller clearance (cs = 0.141 mm) (San Andrés, L., 2012, “Damping and Inertia Coefficients for Two Open Ends Squeeze Film Dampers With a Central Groove: Measurements and Predictions,” ASME J. Eng. Gas Turbines Power, 134(10), p. 102506), show the prior damping and inertia coefficients are larger, ∼5.0 and ∼2.2 times larger than the current ones. These magnitudes agree modestly with theoretical ratios for damping and inertia coefficients scaling as (c/cs)3 = 5.7 and (c/cs) = 1.8, respectively. In spite of the large difference in depths between a groove and a film land, the magnitudes of dynamic pressures recorded at the groove are similar to those in the lands. That is, the groove profoundly affects the dynamic forced response of the test damper. A computational physics model replicates the experimental whirl motions and predicts force coefficients spanning the same range of whirl frequencies, orbit radii, and static eccentricities. The model predictions reproduce with great fidelity the experimental force coefficients. The good agreement relies on the specification of an effective groove depth derived from one experiment.

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