scholarly journals Effects of Fluid Inertia and Turbulence on the Force Coefficients for Squeeze Film Dampers

1986 ◽  
Vol 108 (2) ◽  
pp. 332-339 ◽  
Author(s):  
L. San Andre´s ◽  
J. M. Vance
Keyword(s):  
Squeeze Film ◽  
Fluid Inertia ◽  
High Eccentricity ◽  
Small Eccentricity ◽  
Inertia Effects ◽  
Force Coefficients ◽  
Inertia Coefficient ◽  
Squeeze Film Dampers ◽  
Order Of Magnitude ◽  
Large Eccentricity

The effects of fluid inertia and turbulence on the force coefficients of squeeze film dampers are investigated analytically. Both the convective and the temporal terms are included in the analysis of inertia effects. The analysis of turbulence is based on friction coefficients currently found in the literature for Poiseuille flow. The effect of fluid inertia on the magnitude of the radial direct inertia coefficient (i.e., to produce an apparent “added mass” at small eccentricity ratios, due to the temporal terms) is found to be completely reversed at large eccentricity ratios. The reversal is due entirely to the inclusion of the convective inertia terms in the analysis. Turbulence is found to produce a large effect on the direct damping coefficient at high eccentricity ratios. For the long or sealed squeeze film damper at high eccentricity ratios, the damping prediction with turbulence included is an order of magnitude higher than the laminar solution.

scholarly journals Squeeze-Film Damper Technology: Part 1 — Prediction of Finite Length Damper Performance

1983 ◽  
Author(s):  
J. W. Lund ◽  
A. J. Smalley ◽  
J. A. Tecza ◽  
J. F. Walton
Keyword(s):  
Finite Length ◽  
Gas Turbines ◽  
Squeeze Film ◽  
Fluid Inertia ◽  
Inertia Effects ◽  
Strongly Coupled ◽  
Squeeze Film Damper ◽  
Rotor Systems ◽  
Squeeze Film Dampers ◽  
Calculation Results

Squeeze-film dampers are commonly used in gas turbine engines and have been applied successfully in a great many new designs, and also as retrofits to older engines. Of the mechanical components in gas turbines, squeeze-film dampers are the least understood. Their behavior is nonlinear and strongly coupled to the dynamics of the rotor systems on which they are installed. The design of these dampers is still largely empirical, although they have been the subject of a large number of past investigations. To describe recent analytical and experimental work in squeeze-film damper technology, two papers are planned. This abstract outlines the first paper, Part 1, which concerns itself with squeeze-film damper analysis. This paper will describe an analysis method and boundary conditions which have been developed recently for modelling dampers, and in particular, will cover the treatment of finite length, feed and drain holes and fluid inertia effects, the latter having been shown recently to be of great importance in predicting rotor system behavior. A computer program that solves the Reynolds equation for the above conditions will be described and sample calculation results presented.

scholarly journals Squeeze Film Dampers Executing Small Amplitude Circular-Centered Orbits in High-Speed Turbomachinery

2016 ◽  
Vol 2016 ◽  
pp. 1-16 ◽  
Author(s):  
Sina Hamzehlouia ◽  
Kamran Behdinan
Keyword(s):  
Pressure Distribution ◽  
Small Amplitude ◽  
High Speed ◽  
Fluid Film ◽  
Distribution Model ◽  
Squeeze Film ◽  
Fluid Inertia ◽  
Inertia Effects ◽  
Squeeze Film Dampers ◽  
Reaction Forces

This work represents a pressure distribution model for finite length squeeze film dampers (SFDs) executing small amplitude circular-centered orbits (CCOs) with application in high-speed turbomachinery design. The proposed pressure distribution model only accounts for unsteady (temporal) inertia terms, since based on order of magnitude analysis, for small amplitude motions of the journal center, the effect of convective inertia is negligible relative to unsteady (temporal) inertia. In this work, the continuity equation and the momentum transport equations for incompressible lubricants are reduced by assuming that the shapes of the fluid velocity profiles are not strongly influenced by the inertia forces, obtaining an extended form of Reynolds equation for the hydrodynamic pressure distribution that accounts for fluid inertia effects. Furthermore, a numerical procedure is represented to discretize the model equations by applying finite difference approximation (FDA) and to numerically determine the pressure distribution and fluid film reaction forces in SFDs with significant accuracy. Finally, the proposed model is incorporated into a simulation model and the results are compared against existing SFD models. Based on the simulation results, the pressure distribution and fluid film reaction forces are significantly influenced by fluid inertia effects even at small and moderate Reynolds numbers.

Analysis of Short Squeeze Film Dampers With a Central Groove

1992 ◽  
Vol 114 (4) ◽  
pp. 659-664 ◽  
Author(s):  
Luis A. San Andres
Keyword(s):  
Squeeze Film ◽  
Inertia Force ◽  
Dynamic Force ◽  
Fluid Inertia ◽  
Dynamic Flow ◽  
Low Frequencies ◽  
Squeeze Film Damper ◽  
Force Coefficients ◽  
Squeeze Film Dampers ◽  
Combined Action

A novel analysis for the dynamic force response of a squeeze film damper with a central feeding groove considers the dynamic flow interaction between the squeeze film lands and the feeding groove. For small amplitude centered motions and based on the short bearing model, corrected values for the damping and inertia force coefficients are determined. Correlations with existing experimental evidence is excellent. Analytical results show that the grooved-damper behaves at low frequencies as a single land damper. Dynamic force coefficients are determined to be frequency dependent. Analytical predictions show that the combined action of fluid inertia and groove volume—liquid compressibility affects the force coefficients for dynamic excitation at large frequencies.

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.

The Effect of Fluid Inertia in Squeeze Film Damper Bearings: A Heuristic and Physical Description

1983 ◽  
Author(s):  
John A. Tichy
Keyword(s):  
Hydrodynamic Lubrication ◽  
Turbulence Models ◽  
Squeeze Film ◽  
Squeezing Flow ◽  
Fluid Inertia ◽  
Inertia Effects ◽  
Practical Applications ◽  
Viscous Forces ◽  
Squeeze Film Dampers ◽  
Inertia Forces

Fluid inertia forces are comparable to viscous forces in squeeze film dampers in the range of many practical applications. This statement appears to contradict the commonly held view in hydrodynamic lubrication that inertia effects are small. Upon closer inspection, the latter is true for predominantly sliding (rather than squeezing) flow bearings. The basic equations of hydrodynamic lubrication flow are developed, including the inertia terms. The appropriate orders of magnitude of the viscous and inertia terms are evaluated and compared, for journal bearings and for squeeze film dampers. Exact equations for various limiting cases are presented: low eccentricity, high and low Reynolds number. The asymptotic behavior is surprisingly similar in all cases. Due to inertia, the damper force may shift 90° forward from its purely viscous location. Inertia forces are evaluated for typical damper conditions. The effect of turbulence in squeeze film dampers is also discussed. On physical grounds it is argued that the transition occurs at much higher Reynolds numbers than the usual lubrication turbulence models predict.

Solutions for the Combined Motion of Finite Length Squeeze Film Dampers Around the Bearing Center

1996 ◽  
Vol 118 (3) ◽  
pp. 617-622 ◽  
Author(s):  
J. X. Zhang ◽  
J. B. Roberts
Keyword(s):  
Finite Length ◽  
Wall Stress ◽  
Squeeze Film ◽  
Fluid Inertia ◽  
Mean Flow ◽  
Inertia Effects ◽  
Combined Motion ◽  
Squeeze Film Dampers ◽  
San Andres ◽  
Analytical Expressions

Analytical expressions for the hydrodynamic forces, and four related dynamic coefficients, are presented for finite length squeeze film dampers (SFDs) executing combined radial and tangential motion around the bearing center, with small amplitude. Previous analyses by Mulcahy (1980) and San Andres and Vance (1987) are shown to be particular cases of the present treatment. The influence of combined motion on the coefficients is found to differ, in several respects, from that which can be deduced from results for one dimensional radial motion and circular centred orbital motion. The effects of combined motion on the mean flow velocity and the wall stress are also studied. The study provides further insight into the validity of bulk flow assumptions, often used when dealing with lubrication problems where fluid inertia effects are significant.

Dynamic Characterization of an Integral Squeeze Film Bearing Support Damper for a Supercritical CO2 Expander

2017 ◽  
Author(s):  
Bugra Ertas ◽  
Adolfo Delgado ◽  
Jeffrey Moore
Keyword(s):  
High Speed ◽  
Dynamic Performance ◽  
Mechanical Impedance ◽  
Squeeze Film ◽  
Fluid Inertia ◽  
Inertia Effects ◽  
Damping Behavior ◽  
Impedance Testing ◽  
Stiffness And Damping ◽  
Onset Of Cavitation

The present work advances experimental results and analytical predictions on the dynamic performance of an integral squeeze film damper (ISFD) for application in a high-speed super-critical CO2 (sCO2) expander. The test campaign focused on conducting controlled orbital motion mechanical impedance testing aimed at extracting stiffness and damping coefficients for varying end seal clearances, excitation frequencies, and vibration amplitudes. In addition to the measurement of stiffness and damping; the testing revealed the onset of cavitation for the ISFD. Results show damping behavior that is constant with vibratory velocity for each end seal clearance case until the onset of cavitation/air ingestion, while the direct stiffness measurement was shown to be linear. Measurable added inertia coefficients were also identified. The predictive model uses an isothermal finite element method to solve for dynamic pressures for an incompressible fluid using a modified Reynolds equation accounting for fluid inertia effects. The predictions revealed good correlation for experimentally measured direct damping, but resulted in grossly overpredicted inertia coefficients when compared to experiments.

Extended Finite Element Analysis of Journal Bearing Dynamic Forced Performance to Include Fluid Inertia Force Coefficients

2012 ◽  
Author(s):  
Luis San Andrés
Keyword(s):  
Finite Element ◽  
Test Data ◽  
Small Amplitude ◽  
Forced Response ◽  
Inertia Force ◽  
Fluid Inertia ◽  
Inertia Effects ◽  
Force Coefficients ◽  
Reaction Forces ◽  
Bearing Stiffness

Reynolds equation governs the generation of hydrodynamic pressure in oil lubricated fluid film bearings. The static and dynamic forced response of a bearing is obtained from integration of the film pressure on the bearing surface. For small amplitude journal motions, a linear analysis represents the fluid film bearing reaction forces as proportional to the journal center displacements and velocity components through four stiffness and four damping coefficients. These force coefficients are integrated into rotor-bearing system structural analysis for prediction of the system stability and the synchronous response to imbalance. Fluid inertia force coefficients, those relating reaction forces to journal center accelerations, are routinely ignored because most oil lubricated bearings operate at relatively low Reynolds numbers, i.e., under slow flow conditions. Modern rotating machinery operates at ever increasing surface speeds to deliver more power in smaller size units. Under these operating conditions fluid inertia effects need to be accounted for in the forced response of oil lubricated bearings, as recent experimental test data also reveal. The paper presents a finite element formulation to predict added mass coefficients in oil lubricated bearings by extending a basic formulation that already calculates the bearing stiffness and damping force coefficients. That is, a small amplitude perturbation analysis of the lubrication flow equations keeps the temporal fluid inertia effects and develops a set of equations to obtain the bearing stiffness, damping and inertia force coefficients. The method does not impose on the cost of the original formulation which makes it very attractive for ready implementation in existing software. Predictions of the computational model are benchmarked against archival test data for an oil-lubricated pressure dam bearing supporting large compressors. The comparisons show fluid inertia effects cannot be ignored for operation at high rotor speeds and with small static loads.

Fluid Inertia Effects in a Non-Newtonian Squeeze Film Between Two Plane Annuli

1999 ◽  
Vol 122 (4) ◽  
pp. 872-875 ◽  
Author(s):  
R. Usha and ◽  
P. Vimala
Keyword(s):  
Carrying Capacity ◽  
Integral Method ◽  
Squeeze Flow ◽  
Squeeze Film ◽  
Load Carrying Capacity ◽  
Fluid Inertia ◽  
Inertia Effects ◽  
Load Carrying ◽  
Analytical Expressions ◽  
Plastic Fluids

An analysis is presented for the laminar squeeze flow of an incompressible powerlaw fluid between parallel plane annuli using the modified lubrication theory and energy integral method. The local and the convective inertia of the flow are considered in the investigation. Analytical expressions for the load carrying capacity of the squeeze film are obtained using both the methods and are compared with those based on the assumption of inertialess flow. It is observed that the inertia correction in the load carrying capacity is more significant for pseudo-plastic fluids, n<1.[S0742-4787(00)00504-X]

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