On the Numerical Prediction of Finite Length Squeeze Film Dampers Performance With Free Air Entrainment

2009 ◽  
Vol 132 (1) ◽  
Author(s):  
Tilmer H. Méndez ◽  
Jorge E. Torres ◽  
Marco A. Ciaccia ◽  
Sergio E. Díaz
Keyword(s):  
Finite Length ◽  
Air Entrainment ◽  
Squeeze Flow ◽  
Squeeze Film ◽  
Air Entrapment ◽  
Film Rupture ◽  
Subsequent Formation ◽  
Squeeze Film Dampers ◽  
Entrained Air ◽  
San Andres

Squeeze film dampers (SFDs) are commonly used in turbomachinery to dampen shaft vibrations in rotor-bearing systems. The main factor deterring the success of analytical models for the prediction of SFD’s performance lies on the modeling of dynamic film rupture. Usually, the cavitation models developed for journal bearings are applied to SFDs. Yet, the characteristic motion of the SFD results in the entrapment of air into the oil film, producing a bubbly mixture that cannot be represented by these models. There is a need to identify and understand the parameters that affect air entrainment and subsequent formation of a bubbly air-oil mixture within the lubricant film. A previous model by and Diazand San Andrés (2001, “A Model for Squeeze Film Dampers Operating With Air Entrapment and Validation With Experiments,” ASME J. Tribol., 123, pp. 125–133) advanced estimation of the amount of film-entrapped air based on a nondimensional number that related both geometrical and operating parameters but limited to the short bearing approximation (i.e., neglecting circumferential flow). The present study extends their work to consider the effects of finite length-to-diameter ratios. This is achieved by means of a finite volume integration of the two-dimensional, Newtonian, compressible Reynolds equation combined with the effective mixture density and viscosity defined in the work of Diaz and San Andrés. A flow balance at the open end of the film is devised to estimate the amount of air entrapped within the film. The results show, in dimensionless plots, a map of the amount of entrained air as a function of the feed-squeeze flow number, defined by Diaz and San Andrés, and the length-to-diameter ratio of the damper. Entrained air is shown to decrease as the L/D ratio increases, going from the approximate solution of Diaz and San Andrés for infinitely short SFDs down to no air entrainment for an infinite length SFD. The results of this research are of immediate engineering applicability. Furthermore, they represent a firm step to advance the understanding of the effects of air entrapment on the performance of SFDs.

On the Numerical Prediction of Finite Length Squeeze Film Dampers Performance With Free Air Entrainment

2008 ◽  
Author(s):  
Tilmer H. Me´ndez ◽  
Marco A. Ciaccia ◽  
Jorge E. Torres ◽  
Sergio E. Di´az
Keyword(s):  
Finite Length ◽  
Air Entrainment ◽  
Squeeze Flow ◽  
Squeeze Film ◽  
Infinite Length ◽  
Film Rupture ◽  
Subsequent Formation ◽  
Mixture Density ◽  
Squeeze Film Dampers ◽  
Entrained Air

Squeeze Film Dampers (SFDs) are commonly used in turbomachinery to dampen shaft vibrations in rotor-bearing systems. The main factor deterring the success of analytical models for the prediction of SFD’s performance lays on the modeling of dynamic film rupture. Usually, the cavitation models developed for journal bearings are applied to SFDs. Yet, the characteristic motion of the SFD results in the entrapment of air into the oil film, producing a bubbly mixture that cannot be represented by these models. There is a need to identify and understand the parameters that affect air entrainment and subsequent formation of a bubbly air-oil mixture within the lubricant film. A previous model by Diaz and San Andre´s advanced estimation of the amount of film-entrapped air, based on a non-dimensional number that related both geometrical and operating parameters but limited to the short bearing approximation (i.e., neglecting circumferential flow). The present study extends their work to consider the effects of finite length-to-diameter ratios. This is achieved by means of a finite volume integration of the two-dimensional, Newtonian, compressible Reynolds equation combined with the effective mixture density and viscosity defined in the work of Diaz and San Andre´s. A flow balance at the open end of the film is devised to estimate the amount of air entrapped within the film. The results show, in dimensionless plots, a map of the amount of entrained air as a function of the Feed-Squeeze Flow Number, defined by Diaz and San Andre´s, and the Length-to-Diameter Ratio of the Damper. Entrained air is shown to decrease as the L/D ratio increases, going from the approximate solution of Diaz and San Andre´s for infinitely short SFDs down to no air entrainment for an infinite length SFD. The results of this research are of immediate engineering applicability. Furthermore, they represent a firm step to advance the understanding of the effects of air entrapment on the performance of SFDs.

On the Amount of Air Entrainment Into Finite Length Squeeze Film Dampers

2007 ◽  
Author(s):  
Tilmer Me´ndes ◽  
Marco A. Ciaccia ◽  
Jorge E. Torres ◽  
Sergio E. Di´az
Keyword(s):  
Finite Length ◽  
High Performance ◽  
Air Entrainment ◽  
Squeeze Film ◽  
Dimensionless Number ◽  
Operational Parameters ◽  
Air Entrapment ◽  
Flow Number ◽  
Lubrication Equation ◽  
Squeeze Film Dampers

Squeeze Film Dampers (SFDs) are routinely employed to reduce vibration amplitudes and isolate structural components in gas jet engines, high performance compressors and, occasionally, water pumps. Most open-ended squeeze film dampers in practice present the phenomenon of air entrapment. It is generally accepted that the presence of air reduces the damping capability of the SFD, especially at large amplitudes and high frequencies of vibrations. Thus, there is a need for a reliable model of practical use in the analysis of high performance turbomachinery SDFs operating with air entrainment. Di´az and San Andre´s advance a model for estimation of air entrapped into the film lands. This model is based on a dimensionless number that relates geometric and operational parameters, but is strictly valid only for infinitesimal length bearings. The present research has by objective extending the previous work of Di´az and San Andre´s for prediction of air entrainment and entrapment on finite length bearings. The Reynolds lubrication equation for a homogeneous mixture is solved using the finite volume method. The results are shown in a map that allows determining air volume content in the film as a function of the dimensionless parameter created by Di´az and San Andre´s (Squeeze-Feed Flow Number, γ) and the length-diameter ratio (L/D). This work represents a significant step towards a better understanding of air entrainment in finite length Squeeze Film Dampers.

Finite Length Squeeze Film Dampers With Air Entrainment: Non-Dimensional Maps and Their Applicability

2010 ◽  
Author(s):  
Jorge E. Torres ◽  
Sergio E. Di´az
Keyword(s):  
Finite Length ◽  
Dynamic Performance ◽  
Air Entrainment ◽  
Operating Conditions ◽  
Squeeze Flow ◽  
Squeeze Film ◽  
Flow Number ◽  
Squeeze Film Dampers ◽  
Entrapped Air ◽  
Volume Method

Squeeze Film Dampers (SFDs) are bearings that support large motion amplitudes when traversing rotor-bearing systems critical speeds. Actual practice demands bearings with operating conditions of low oil supply pressure and high frequency. In open-ended SFDs, large amplitudes of journal motion draw air into the film gap. The air ingested and entrapped results in a bubbly mixture that affects the dynamic performance and the overall damping capability of the SFDs. Diaz and San Andre´s [11] developed a model to predict the amount of air ingested into SFDs with open-ends. They proposed an innovative non-dimensional number to estimate the amount of air entrapped in the film gap, but their analytical results are limited to short length bearings. Mendez et al. [13] extended the results of Diaz and San Andre´s to finite length bearings, devising a Finite Volume Method (FVM) scheme. Even though their research presented new and significant results, they lack wider applicability that includes different geometries or boundary conditions. The present research proposes the solution of the Reynolds equation by the finite element method. Results computed by this formulation explore non-dimensional maps for determination of the amount of entrapped air. The results show that for fixed lubricant properties the amount of entrapped air depends exclusively on three dimensionless parameters: feed-squeeze flow number, length to diameter ratio, and dimensionless orbit radius.

A Theoretical Model for Squeeze Film Dampers Operating with Air Entrainment

2007 ◽  
Vol 353-358 ◽  
pp. 1683-1687
Author(s):  
Chun Yu Zhao ◽  
Hong Liang Yao ◽  
Feng Lin ◽  
Bang Chun Wen
Keyword(s):  
Hydrodynamic Lubrication ◽  
Control Volume ◽  
Air Entrainment ◽  
Ideal Gas ◽  
Squeeze Film ◽  
Computational Domain ◽  
Squeeze Film Dampers ◽  
Hydrodynamic Lubrication Theory ◽  
Volume Method ◽  
San Andres

A continuum model of the evolution of air ingestion and entrainment for open-ended squeeze film dampers is proposed in this paper. Hydrodynamic lubrication theory is extended to lubrication with mixture of a Newtonian liquid and an ideal gas. The solution to the universal Reynolds equation is determined numerically using a control volume method (Elrod algorithm) and the forth-order Range-Kutta method. This method conserves mass throughout the computational domain including air ingestion and entrainment. Excellent agreement is found with the experimental works of Diaz and San Andrès for the squeeze film damper [1, 2].

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.

Comparison of Air Ingestion vs. Dimensionless Parameters in Squeeze Film Dampers

2009 ◽  
Author(s):  
Jorge E. Torres ◽  
Sergio E. Diaz
Keyword(s):  
High Speed ◽  
Volume Fraction ◽  
Air Entrainment ◽  
Industrial Applications ◽  
Squeeze Flow ◽  
Squeeze Film ◽  
Dimensionless Number ◽  
Damping Capacity ◽  
Flow Number ◽  
Squeeze Film Dampers

Ingestion and entrainment of air into the Squeeze Film Dampers (SFDs) with open end result in a bubbly mixture that affects their damping capacity. The industrial applications demand dampers with low pressure supply and operating high speed, it means, it exists a necessity of propose a model to predict the air ingestion in this kind of bearing. Diaz and San Andre´s reported results of an extend research to quantify the effect bubbly mixture in the performance of the SFDs. They also advanced an analytic model for short infinity bearings (L/D = 0) which estimate the air ingestion as function of non-dimensional number named by them feed squeeze flow number. Me´ndez et al. advanced the understanding of the effect air entrainment. They propose a new dimensionless map to estimate the air volume fraction in finite length bearings. Although, their results are immediate applicability, they do not have been validated. The present work looks for confirm the results presented by Me´ndez et al. To achieve this, it is solved a compressible Reynold equation with a different numerical method. The results indicate that is necessary another dimensionless number to estimate the entrapment air and the dimensionless map proposed by Me´ndez et al. is valid only to bearings with an eccentricity-clearing ratio of 0.5248.

A Model for Squeeze Film Dampers Operating With Air Entrainment and Validation With Experiments

2000 ◽  
Vol 123 (1) ◽  
pp. 125-133 ◽  
Author(s):  
Sergio Diaz ◽  
Luis San Andre´s
Keyword(s):  
Air Entrainment ◽  
Operating Conditions ◽  
Squeeze Film ◽  
Practical Implementation ◽  
Engineering Practice ◽  
Film Rupture ◽  
Mixture Flow ◽  
Actual Performance ◽  
Conventional Film ◽  
Squeeze Film Dampers

Squeeze film dampers (SFDs) reduce vibrations and aid in suppressing instabilities in high performance rotor-bearing systems. However, air ingestion and entrapment, pervasive in open-ended dampers with low supply pressures, leads to a bubbly lubricant that severely reduces the dynamic film forces and the overall damping capability. Analyses based on conventional film rupture models, vapor or gaseous lubricant cavitation, fail to predict the actual performance of SFDs, and thus lack credibility in engineering practice. A modified Reynolds equation for prediction of the pressure in a homogeneous bubbly mixture flow is advanced along with an empirical formula for estimation of the amount of air entrained in an open-ended damper. Careful experimentation in a test SFD operating with controlled bubbly mixtures and freely entrained air evidenced similar physical behavior, guided the analytical developments, and provided the basis for validation of the model forwarded. Comparisons of predictions and test results show a fair correlation. A simple equation to predict the amount of air ingestion is also advanced in terms of the damper geometry, supplied flow and operating conditions. The criterion may lack practical implementation since the persistence of air entrainment increases with the frequency and amplitude of journal motions, unless enough lubricant is supplied at all operating conditions.

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.

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