Force Coefficients for a Centrally Grooved Short Squeeze Film Damper

1996 ◽  
Vol 118 (3) ◽  
pp. 608-616 ◽  
Author(s):  
J. X. Zhang ◽  
J. B. Roberts
Keyword(s):  
Hydrodynamic Force ◽  
Theoretical Work ◽  
Experimental Results ◽  
Squeeze Film ◽  
Static Force ◽  
Squeeze Film Damper ◽  
Force Coefficients ◽  
Supply Pressure ◽  
Supply Mechanism ◽  
Good Agreement

A centrally grooved short squeeze film damper (SFD), together with its lubricant supply mechanism (LSM), is analyzed, using an integrated theoretical model. It is shown that the traditional analysis for such a damper, where the effects of the central groove and the LSM are ignored, can lead to a seven-fold underestimation of the magnitude of the hydrodynamic force coefficients. The new theory gives predictions for the damping coefficients which are in good agreement with corresponding experimental results. Moreover, a five-fold improvement is obtained for both the temporal and convective inertia coefficients, at low values of eccentricity. The new model leads to the prediction of a nonzero fluid static force which, in conformity with experimental results, is linearly related to the supply pressure. The existence of this static force has not been explained by previous theoretical work on SFDs.

Identification of Non-Linear Force Coefficients for the Radial Motion of a Squeeze Film Damper

1994 ◽  
Vol 208 (4) ◽  
pp. 235-245 ◽  
Author(s):  
J X Zhang ◽  
J B Roberts
Keyword(s):  
Experimental Data ◽  
Linear Model ◽  
Radial Motion ◽  
Squeeze Film ◽  
Static Force ◽  
Fluid Force ◽  
Squeeze Film Damper ◽  
Force Coefficients ◽  
Supply Pressure ◽  
Non Linear

The fluid force generated in a squeeze film damper undergoing large amplitude radial motion is described in terms of non-linear hydrodynamic inertial and damping coefficients, together with afluid static force. Linear-in-the-parameter polynomial forms are introduced to represent the variation of these contributions with radial position. A generalized state variable filter identification method is developed which enables all the parameters in the non-linear model to be estimated from experimental data. The method is validated by processing simulated data and then applied to some new experimental data. Experimental results, relating to the influence of the supply pressure and the operating frequency on the coefficients, are presented and discussed. Comparisons are made with corresponding predictions derived from existing lubrication theory. The parametric non-linear model is found to give a good fit to experimental data over a significant region within the vicinity of the initial static equilibrium position. Through a combination of results, the variation of the fluid force coefficients and the fluid static force with eccentricity, over nearly the whole range of the radial clearance, is obtained. Temporal inertia is found to be more important than convective inertia for motion near the centre of the clearance circle. The existence of a fluid static force, suggested by previous work is confirmed. It is found that this force is linearly proportional to the oil supply pressure.

Perturbation Solutions for Eccentric Operation of Squeeze Film Damper Systems

1986 ◽  
Vol 108 (4) ◽  
pp. 619-623 ◽  
Author(s):  
Xuehai Li ◽  
D. L. Taylor
Keyword(s):  
Numerical Simulation ◽  
Experimental Results ◽  
Squeeze Film ◽  
Rigid Rotor ◽  
Squeeze Film Damper ◽  
Synchronous Motion ◽  
Squeeze Film Dampers ◽  
Large Speed ◽  
Good Agreement ◽  
Perturbation Solutions

The study focuses on the effect of a small unidirectional load such as comes from imperfect balance between preloading on centering springs and gravitational load on squeeze film dampers. A rigid rotor-squeeze film damper system is considered, and a thorough study of the synchronous motion of the system is performed. Two perturbation solutions are developed: one for large speed and one for small speed. The perturbation solutions are shown to be in good agreement with numerical simulation and published experimental results.

A theoretical and experimental investigation into the vibration response of a flexible rotor and squeeze-film damper assembly

2001 ◽  
Vol 215 (10) ◽  
pp. 1251-1269 ◽  
Author(s):  
C-C Siew ◽  
M Hill ◽  
R Holmes ◽  
M Brennan
Keyword(s):  
Harmonic Balance ◽  
Three Dimensional ◽  
Harmonic Balance Method ◽  
Vibration Response ◽  
Mode Shapes ◽  
Squeeze Film ◽  
Flexible Rotor ◽  
Linear Vibration ◽  
Squeeze Film Damper ◽  
Good Agreement

This paper presents two efficient methods to calculate the unbalance vibration response of a flexible rotor provided with a squeeze-film damper (SFD) with retainer springs. Both methods are iterative and combine the harmonic balance and receptance approaches. The first method, called the modified iteration method (MIM), is suitable for predicting the three-dimensional mode shapes of a concentric SFD-rotor system. The second method, called the modified harmonic balance method (MHBM), is developed to calculate the non-linear vibration response of a flexible shaft provided with either a concentric or eccentric SFD. The system is also investigated experimentally under different conditions. The predictions computed by these methods are compared with experimental measurements and reasonably good agreement is obtained.

Study of Static Fluid Forces in a Squeeze Film Damper with a Circumferential Groove

1995 ◽  
Vol 209 (4) ◽  
pp. 263-274
Author(s):  
J X Zhang
Keyword(s):  
Fluid Pressure ◽  
Squeeze Film ◽  
Fluid Inertia ◽  
Traditional Use ◽  
Fluid Force ◽  
Squeeze Film Damper ◽  
Fluid Forces ◽  
Supply Pressure ◽  
Static Fluid ◽  
Approximate Expressions

Approximate expressions are obtained for static fluid pressure and force for a centrally grooved squeeze film damper (SFD) resting at an equilibrium position without vibration. The analysis shows that, to some extent, grooved SFDs may share some characteristics with hydrostatic bearings, due to the existence of the lubricant supply pressure. Thus static fluid force and hence oil stiffness may exist in SFDs, in addition to the conventional inertial and damping coefficients for SFDs. This paper is solely focused on the static fluid forces and oil stiffness generated in an SFD with a finite length groove. Flow continuity is used at the centre of the groove, which takes into account the effects of the inlet oil flowrate and oil supply pressure. This use of flow continuity differs substantially from the traditional use of constant pressure in the central groove, and it provides better results. At the interface between the groove and the thin film land, a step bearing model with ignored fluid inertia is employed. It is verified by both the theory and previous experiments that the static fluid force and stiffness are linearly proportional to both the lubricant supply pressure and the eccentricity ratio of the SFD journal.

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.

Forced Response of a Squeeze Film Damper and Identification of Force Coefficients From Large Orbital Motions

2004 ◽  
Vol 126 (2) ◽  
pp. 292-300 ◽  
Author(s):  
Luis San Andre´s ◽  
Oscar De Santiago
Keyword(s):  
Excitation Frequency ◽  
Air Entrainment ◽  
Forced Response ◽  
Effective Length ◽  
Single Frequency ◽  
Squeeze Film ◽  
Inertia Force ◽  
Damping Force ◽  
Squeeze Film Damper ◽  
Force Coefficients

Experimentally derived damping and inertia force coefficients from a test squeeze film damper for various dynamic load conditions are reported. Shakers exert single frequency loads and induce circular and elliptical orbits of increasing amplitudes. Measurements of the applied loads, bearing displacements and accelerations permit the identification of force coefficients for operation at three whirl frequencies (40, 50, and 60 Hz) and increasing lubricant temperatures. Measurements of film pressures reveal an early onset of air ingestion. Identified damping force coefficients agree well with predictions based on the short length bearing model only if an effective damper length is used. A published two-phase flow model for air entrainment allows the prediction of the effective damper length, and which ranges from 82% to 78% of the damper physical length as the whirl excitation frequency increases. Justifications for the effective length or reduced (flow) viscosity follow from the small through flow rate, not large enough to offset the dynamic volume changes. The measurements and analysis thus show the pervasiveness of air entrainment, whose effect increases with the amplitude and frequency of the dynamic journal motions. Identified inertia coefficients are approximately twice as large as those derived from classical theory.

Squeeze Film Damper With a Mechanical End Seal: Experimental Force Coefficients Derived From Circular Centered Orbits

2008 ◽  
Vol 130 (4) ◽  
Author(s):  
Luis San Andrés ◽  
Adolfo Delgado
Keyword(s):  
Dry Friction ◽  
Dynamic Pressure ◽  
Test System ◽  
Single Frequency ◽  
Squeeze Film ◽  
Mechanical Seal ◽  
Damping Force ◽  
Squeeze Film Damper ◽  
Force Coefficients ◽  
Aircraft Application

The paper presents parameter identification measurements conducted on a squeeze film damper (SFD) featuring a nonrotating mechanical seal that effectively eliminates lubricant side leakage. The SFD-seal arrangement generates dissipative forces due to viscous and dry-friction effects from the lubricant film and surfaces in contact, respectively. The test damper reproduces an aircraft application that must contain the lubricant for extended periods of time. The test damper journal is 2.54cm in length and 12.7cm in diameter, with a nominal clearance of 0.127mm. The damper feed end opens to a plenum filled with lubricant, and at its discharge grooved section, four orifice ports evacuate the lubricant. In earlier publications, single frequency force excitation tests were conducted, without and with lubricant in the squeeze film land, to determine the seal dry-friction force and viscous damping force coefficients. Presently, further measurements are conducted to identify the test system and SFD force coefficients using two sets of flow restrictor orifice sizes (2.8mm and 1.1mm in diameter). The flow restrictors regulate the discharge flow area and thus control the oil flow through the squeeze film. The experiments also include measurements of dynamic pressures at the squeeze film land and at the discharge groove. The magnitude of dynamic pressure in the squeeze film land is nearly identical for both sets of flow restrictors, and for small orbit radii, dynamic pressures in the discharge groove have peak values similar to those in the squeeze film land. The identified parameters include the test system damping and the individual contributions from the squeeze film, dry friction in the mechanical seal and structure remnant damping. The identified system damping coefficients are frequency and motion amplitude dependent due to the dry-friction interaction at the mechanical seal interface. Squeeze film force coefficients, damping and added mass, are in agreement with simple predictive formulas for an uncavitated lubricant condition and are similar for both flow restrictor sizes. The SFD-mechanical seal arrangement effectively prevents air ingestion and entrapment and generates predicable force coefficients for the range of frequencies tested.

Identification of Force Coefficients in a Squeeze Film Damper With a Mechanical End Seal: Centered Circular Orbit Tests

2007 ◽  
Author(s):  
Luis San Andre´s ◽  
Adolfo Delgado
Keyword(s):  
Dry Friction ◽  
Dynamic Pressure ◽  
Test System ◽  
Single Frequency ◽  
Squeeze Film ◽  
Mechanical Seal ◽  
Damping Force ◽  
Squeeze Film Damper ◽  
Force Coefficients ◽  
Aircraft Application

The paper presents parameter identification measurements conducted on a squeeze film damper (SFD) featuring a non-rotating mechanical seal that effectively eliminates lubricant side leakage. The SFD-seal arrangement generates dissipative forces due to viscous and dry-friction effects from the lubricant film and surfaces in contact, respectively. The test damper reproduces an aircraft application that must contain the lubricant for extended periods of time. The test damper journal is 2.54 cm in length and 12.7 cm in diameter, with a nominal clearance of 0.127 mm. The damper feed end opens to a plenum filled with lubricant, and at its discharge grooved section, four orifice ports evacuate the lubricant. In prior publications (ASME Paper GT2006-90782, IJTC2006-12041), single frequency force excitation tests were conducted, without and with lubricant in the squeeze film land, to determine the seal dry-friction force and viscous damping force coefficients. Presently, further measurements are conducted to identify the test system and SFD force coefficients using two sets of flow restrictor orifice sizes (2.8 mm and 1.1 mm in diameter). The flow restrictors regulate the discharge flow area, and thus control the oil flow through the squeeze film. The experiments also include measurements of dynamic pressures at the squeeze film land and at the discharge groove. The magnitude of dynamic pressure in the squeeze film land is nearly identical for both sets of flow restrictors, and for small orbit radii, dynamic pressures in the discharge groove have peak values similar to those in the squeeze film land. The identified parameters include the test system damping and the individual contributions from the squeeze film, dry friction in the mechanical seal and structure remnant damping. The identified system damping coefficients are frequency and motion amplitude dependent due to the dry friction interaction at the mechanical seal interface. Squeeze film force coefficients, damping and added mass, are in agreement with simple predictive formulas for an uncavitated lubricant condition and are similar for both flow restrictor sizes. The SFD-mechanical seal arrangement effectively prevents air ingestion and entrapment and generates predicable force coefficients for the range of frequencies tested.

Sign in / Sign up

Export Citation Format

Share Document