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 Andres ◽  
Bryan Rodríguez
Keyword(s):  
Dynamic Pressure ◽  
Effective Means ◽  
Check Valve ◽  
Physical Space ◽  
Forced Response ◽  
Squeeze Film ◽  
Dynamic Force ◽  
Viscous Damping ◽  
Frequency Independent ◽  
Support Element

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) 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 lubricated with ISO VG2 oil supplied at a low pressure. 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. The experimental results identify the test rig structure, ORs and SFD force coefficients; namely stiffness, mass and viscous damping. The ORs coefficients are frequency independent and show a sizeable direct stiffness along with a quadrature stiffness demonstrative of material damping. 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. 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.

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.

Effect of a Circumferential Feeding Groove on the Dynamic Force Response of a Short Squeeze Film Damper

1994 ◽  
Vol 116 (2) ◽  
pp. 369-376 ◽  
Author(s):  
G. L. Arauz ◽  
L. San Andres
Keyword(s):  
Flow Model ◽  
Dynamic Pressure ◽  
Squeeze Film ◽  
Dynamic Force ◽  
Force Response ◽  
Squeeze Film Damper ◽  
Circumferential Groove ◽  
Damping Characteristics ◽  
Radial Forces ◽  
Lubricant Viscosity

The effect of a circumferential feeding groove on the dynamic force response of a short length, open end squeeze film damper is studied experimentally. Damper configurations with increasing groove depths and journal orbit radii were tested for several conditions of whirl frequency and lubricant viscosity. Significant levels of dynamic pressure were measured at the circumferential groove, and relatively large tangential (damping) forces are produced at the groove which contribute considerably to the damping characteristics of the SFD test articles. Radial forces of substantial magnitude are determined at the groove and at the thin film land where the squeeze film Reynolds number is typically less than 1. The circumferential groove is thought to induce an inertia like effect into the film land. The experimental results correlate well with the predictions from a groove volume-circumferential flow model developed.

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.

Characterization of Foil Bearing Structure for Increasing Shaft Temperatures: Part II—Dynamic Force Performance

2008 ◽  
Author(s):  
Tae Ho Kim ◽  
Luis San Andre´s ◽  
Anthony W. Breedlove
Keyword(s):  
Friction Coefficient ◽  
Dry Friction ◽  
Excitation Frequency ◽  
Forced Response ◽  
Dynamic Loads ◽  
Dynamic Force ◽  
Viscous Damping ◽  
Structural Stiffness ◽  
Foil Bearing ◽  
Excitation Frequencies

The forced response of a gas foil bearing (GFB), a typical rotor support in oil-free microturbomachinery, relies heavily on its resilient bump-strip layers structure, which also offers dry-friction type damping to ameliorate rotor vibrations. Operation at high temperature not only changes the FB elastic support material properties, but also produces thermal growth of the rotor and bearing components which ultimately affect the bearing structural stiffness and energy dissipation characteristics. The paper presents dynamic shaker load versus foil bearing structural deflection measurements for increasing shaft temperatures, from ambient to 188°C. In the tests, a FB supported on a non-rotating shaft is excited with a shaker at three load amplitudes (13 N, 22 N, and 31 N) and frequencies ranging from 40 to 200 Hz. A mechanical impedance model identifies the frequency dependent FB structural stiffness and equivalent viscous damping coefficient or dry-friction coefficient. Surface plots show trends in test results across increasing dynamic loads, shaft temperatures, and excitation frequencies. The FB stiffness increases by as much as 50% with dynamic loads amplitudes increasing from 13 N to 31 N. The stiffness nearly doubles from low to high frequencies; and most importantly, it decreases by a third as the shaft temperature rises to 188°C. In general, the FB dynamic structural stiffness is lower than its static stiffness, reported in a companion paper, at low excitation frequencies, while it becomes larger with increasing excitation frequency due apparently to a bump slip-stick phenomenon. The bearing viscous damping is inversely proportional to the amplitude of dynamic load, excitation frequency, and shaft temperature. The FB structure dry-friction coefficient decreases with increasing amplitude of applied load and shaft temperature, and increases with increasing excitation frequency. The experimental results demonstrate the paramount effect of operating temperature on the structural parameters of a foil bearing.

Experimental Study on the Effect of a Circumferential Feeding Groove on the Dynamic Force Response of a Sealed Squeeze Film Damper

1996 ◽  
Vol 118 (4) ◽  
pp. 900-905 ◽  
Author(s):  
G. L. Arauz ◽  
Luis San Andres
Keyword(s):  
Piston Ring ◽  
Dynamic Pressure ◽  
Squeeze Film ◽  
Dynamic Force ◽  
Force Response ◽  
Flow Conditions ◽  
Squeeze Film Damper ◽  
Circumferential Groove ◽  
Damping Characteristics ◽  
Radial Forces

The influence of a circumferential feeding groove on the dynamic force response of a sealed squeeze film damper is determined experimentally. The damper is sealed by means of a serrated piston ring located at the discharge end of the damper. Damper configurations with two different groove depths and journal orbit radii were tested at increasing whirl frequencies. Large levels of dynamic pressure were measured at the circumferential groove, and relatively large tangential (damping) forces are produced at the groove which contribute considerably to the damping characteristics of the test damper. Radial forces were also determined at the feeding groove and at the film land for uncavitated flow conditions.

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.

Model and Experimental Verification of the Dynamic Forced Performance of a Tightly Sealed Squeeze Film Damper Supplied With a Bubbly Mixture

2019 ◽  
Vol 142 (1) ◽  
Author(s):  
Luis San Andrés ◽  
Bonjin Koo
Keyword(s):  
Sliding Friction ◽  
Volume Fraction ◽  
Dynamic Pressure ◽  
Mechanical Energy ◽  
Added Mass ◽  
Single Frequency ◽  
Squeeze Film ◽  
Radial Clearance ◽  
Force Coefficients ◽  
Supply Pressure

Abstract Practice and experiments with squeeze film dampers (SFDs) sealed with piston rings (PRs) show the lubricant exits through the PR slit, i.e., the gap made by the PR abutted ends when installed, forced as a jet during the portion of a rotor whirl cycle generating a positive squeeze film pressure. In the other portion of a whirl cycle, a subambient dynamic pressure ingests air into the film that mixes with the lubricant to produce a bubbly mixture. To reduce persistent air ingestion, commercial air breathing engines utilizing PRSFDs demand of a sufficiently large lubricant supply pressure (Ps), and hence a larger flow rate that is proportional to the journal squeeze velocity (vs = amplitude r × frequency of motion ω). The stringent requirement clearly limits the applicability and usefulness of SFDs. This paper presents a computational physics model for a sealed-end SFD operating with a mixture and delivers predictions benchmarked against profuse laboratory test data. The model implements a Reynolds equation adapted for a homogeneous bubbly mixture, includes temporal fluid inertia effects, and uses physics-based inlet and outlet lubricant conditions through feed holes and PR slit, respectively. In the experiments for model validation, a SFD damper, 127 mm in diameter D, film land length L = 25.4 mm (L/D = 0.2), and radial clearance c = 0.371 mm, is supplied with an air in ISO VG2 oil bubbly mixture of known gas volume fraction (GVF), zero (pure oil) to 50% in steps of 10%. The mixture supply pressure varies from Ps = 2.06 bar-g (30 psig) to 6.20 bar-g (90 psig). Located in grooves at the top and bottom of the journal, a PR and an O-ring (OR) seal the film land. The OR does not allow any oil leakage or air ingestion; hence, the supplied mixture discharges through the PR slit into a vessel submerged within a large volume of lubricant. Dynamic load tests with a single frequency ω, varying from 10 Hz to 60 Hz, produce circular centered orbits (CCO) with amplitude r = 0.2c. The measurements record the exerted forces and journal motions and an analysis delivers force coefficients, damping and inertia, representative of the exerted frequency range. The model predicts the pressure field and evolution of the GVF within the film land and, in a simulated process replicating the experimental procedure, delivers representative force coefficients. For all Ps conditions, both predictions and tests show the SFD added mass coefficients significantly decrease as the inlet GVF (βs) increases. The experimentally derived damping coefficients do not show a significant change, except for tests with the largest concentration of air (βs = 0.5). The predicted damping differs by 10% with the test derived coefficient which does not readily decrease as the inlet GVF (βs) increases. The added mass coefficients, test and predicted, decrease with βs, both being impervious to the magnitude of supply pressure. The test PRSFD shows a quadrature stiffness due to the sliding friction between the PR being pushed against the journal. An increase in supply pressure exacerbates this unique stiffness that may impair the action of the squeeze film to dissipate mechanical energy. The comprehensive test results, first of their kind, demonstrate that accurate modeling of SFDs operating with air ingestion remains difficult as the flow process and the paths of its major components (air and liquid) are rather complex.

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.

Reduction of the Dynamic Load Capacity in a Squeeze Film Damper Operating With a Bubbly Lubricant

1999 ◽  
Vol 121 (4) ◽  
pp. 703-709 ◽  
Author(s):  
S. E. Diaz ◽  
L. A. San Andre´s
Keyword(s):  
Volume Fraction ◽  
Load Capacity ◽  
Effective Means ◽  
Theoretical Models ◽  
Operating Conditions ◽  
Qualitative Description ◽  
Squeeze Film ◽  
Damping Force ◽  
Hydrostatic Force ◽  
Discharge Pressure

Squeeze film dampers (SFDs) are effective means to reduce vibrations and to suppress instabilities in rotor-bearing systems. However, at operating conditions while traversing critical speeds with large orbital whirl motions, ingestion and entrapment of air into the thin lands of SFDs generates a bubbly mixture (air in lubricant) that is known to reduce the dynamic film pressures and the overall damping capability. This pervasive phenomenon lacks proper physical understanding and sound analytical modeling. An experimental investigation to quantify the forced performance of a SFD operating with a controlled bubbly mixture is detailed. Tests are conducted in a constrained circular orbit SFD to measure the dynamic squeeze film pressures and journal motion at two whirl frequencies (8.33 and 16.67 Hz) as the air content in the mixture increases from 0 percent to 100 percent. The analysis of period-averaged film pressures reveals a zone of uniform low pressure of magnitude equal to the discharge pressure, independently of the mixture composition. The uniform pressure zone extends as the mixture void fraction increases. Radial and tangential film forces are estimated from the dynamic pressures at two axial locations of measurement. The tangential (damping) force decreases proportionally with the mixture volume fraction, while a radial hydrostatic force remains nearly invariant. The experimental results quantify effects previously known by qualitative description only, thus providing a benchmark towards the development of sound theoretical models.

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