An Experimental Study of Nonlinear Oil-Film Forces in a Tilting-Pad Journal Bearing

2015 ◽  
Author(s):  
Phuoc Vinh Dang ◽  
Steven Chatterton ◽  
Paolo Pennacchi ◽  
Andrea Vania ◽  
Filippo Cangioli
Keyword(s):  
High Speed ◽  
Nonlinear Models ◽  
Reaction Force ◽  
Taylor Series Expansion ◽  
Test Model ◽  
Oil Film ◽  
Hydrodynamic Bearing ◽  
Dynamic Coefficients ◽  
Stiffness And Damping ◽  
Tilting Pad Journal Bearing

Journal bearings have been widely used in high-speed rotating machinery. The dynamic coefficients of oil-film force affect the machine unbalance response and machine stability. The oil-film force of hydrodynamic bearing is often characterized by a set of linear stiffness and damping coefficients. However the linear oil-film coefficients with respect to an equilibrium position of the journal are inaccurate when the bearing system vibrates with large amplitudes due to a dynamic load. The study on nonlinear oil-film forces is still rare and most papers are confined to theoretical analyses. The purpose of this paper is to derive some new non-linear force models (28-co., 24-co. and 36-co. models) to identify these dynamic coefficients based on experimental data. The fundamental test model is obtained from a Taylor series expansion of bearing reaction force. Tests were performed with a nominal diameter of 100mm and a length–to–diameter ratio of 0.7 using a suitable test rig in which it is possible to apply the static load in any direction. The results show that these three models are feasible to identify the oil-film forces in which the second-order oil-film coefficients received from the 24-co. model are more stable compared to those of other two nonlinear models.

Experimental Study on Dynamic Coeffcients of Water Lubricated High-Speed Hybrid Bearings With Stepped Recesses

2012 ◽  
Author(s):  
Lin Wang ◽  
Hua Xu ◽  
Shilei Ma
Keyword(s):  
High Speed ◽  
Operating Parameters ◽  
Test Rig ◽  
Oil Film ◽  
Hydrodynamic Bearing ◽  
Rotating Speed ◽  
Dynamic Coefficients ◽  
Supply Pressure ◽  
Hybrid Bearing ◽  
Bearing System

In general, the oil-film forces can be characterized by linear oil-film coefficients of hydrodynamic bearing. This paper proposes an experimental method to recognize the dynamic coefficients of a water lubricated high-speed hybrid bearing with stepped recesses. A test rig is constructed and experimental data are acquired under different conditions. And the unbalance responses method is used to identify the dynamic coefficients of the hybrid bearing system. Comparisons are made to verify the validity and accuracy of the theoretical analysis. The influence of operating parameters, such as supply pressure and rotating speed, on the dynamic coefficients of the system is discussed. The results indicate that the dynamic coefficients increase with the rotating speed when the supply pressure is low.

The Influence of Pad Pivot Elastic Deformation on Static and Dynamic Coefficients for Fixed-Tilting Pad Journal Bearing

2017 ◽  
Author(s):  
Tian Jiale ◽  
Yang Baisong ◽  
Sun Yanhua ◽  
Yu Lie ◽  
Zhou Jian
Keyword(s):  
Elastic Deformation ◽  
High Speed ◽  
Journal Bearing ◽  
Dynamic Stiffness ◽  
Dynamic Performance ◽  
Oil Film ◽  
Dynamic Coefficients ◽  
Tilting Pad ◽  
Two Factors ◽  
Tilting Pad Journal Bearing

High-speed and heavy-loaded rotating machinery require accurate prediction of rotor’s response and stability, which can be characterized by the static and dynamic coefficients of the bearing support. In this paper, a theoretical study has been done to investigate the performance of a fixed-tilting pad journal bearing with ball-in-socket pivot. The analytical model is established with the flexibility of the pad pivot and turbulent effect of the oil film both taken consideration. Under such situation, the pad pivot elastic deformation and its stiffness are calculated using Hertz Contact Theory for various operating points of the rotor-bearing system. The finite element method is adopted to simulate the static coefficients of the fixed-tilting pad bearing, obtaining its oil film pressure distribution varied with the bearing eccentricity ratio. The corresponding dynamic stiffness and damping of the oil film are solved using partial derivative method. In addition, a special interest is put in investigating the effect of the series complex stiffness of the oil film and pad pivot, according to which, the equivalent dynamic characteristics are obtained. The results show that the relation between these two factors are complex and interactive, both of which have a significant influence on the static and dynamic performance of the bearing.

Calculation and Measurement of the Stiffness and Damping Coefficients for a Low Impedance Hydrodynamic Bearing

1997 ◽  
Vol 119 (1) ◽  
pp. 57-63 ◽  
Author(s):  
M. J. Goodwin ◽  
P. J. Ogrodnik ◽  
M. P. Roach ◽  
Y. Fang
Keyword(s):  
Experimental Data ◽  
Dynamic Stiffness ◽  
Perturbation Technique ◽  
The Novel ◽  
Oil Film ◽  
Hydrodynamic Bearing ◽  
Damping Coefficients ◽  
Stiffness And Damping ◽  
Film Stiffness ◽  
Novel Design

This paper describes a combined theoretical and experimental investigation of the eight oil film stiffness and damping coefficients for a novel low impedance hydrodynamic bearing. The novel design incorporates a recess in the bearing surface which is connected to a standard commercial gas bag accumulator; this arrangement reduces the oil film dynamic stiffness and leads to improved machine response and stability. A finite difference method was used to solve Reynolds equation and yield the pressure distribution in the bearing oil film. Integration of the pressure profile then enabled the fluid film forces to be evaluated. A perturbation technique was used to determine the dynamic pressure components, and hence to determine the eight oil film stiffness and damping coefficients. Experimental data was obtained from a laboratory test rig in which a test bearing, floating on a rotating shaft, was excited by a multi-frequency force signal. Measurements of the resulting relative movement between bearing and journal enabled the oil film coefficients to be measured. The results of the work show good agreement between theoretical and experimental data, and indicate that the oil film impedance of the novel design is considerably lower than that of a conventional bearing.

Development of an Efficient Oil Film Damper for Improving the Control of Rotor Vibration

1991 ◽  
Vol 113 (4) ◽  
pp. 557-562 ◽  
Author(s):  
Shiping Zhang ◽  
Litang Yan
Keyword(s):  
High Speed ◽  
Porous Metal ◽  
Porous Matrix ◽  
Squeeze Film ◽  
Oil Film ◽  
Squeeze Film Damper ◽  
Outer Race ◽  
Typical Experiment ◽  
Stiffness And Damping ◽  
Film Stiffness

An efficient oil film damper known as a porous squeeze film damper (PSFD) was developed for more effective and reliable vibration control of high-speed rotors based on the conventional squeeze film damper (SFD). The outer race of the PSFD is made of permeable sintered porous metal materials. The permeability allows some of the oil to permeate into and seep out of the porous matrix, with remarkable improvement of the squeeze film damping properties. The characteristics of PSFD oil film stiffness and damping coefficients and permeability, and also, the steady-state unbalance response of a simple rigid rotor and flexible Jeffcott’s rotor supported on PSFD and SFD are investigated. A typical experiment is presented. Investigations show that the nonlinear vibration characteristics of the unpressurized SFD system such as bistable jump phenomena and “lockup” at rotor pin-pin critical speeds could be avoided and virtually disappear under much greater unbalance levels with properly designed PSFD system. PSFD has the potential advantage of operating effectively under relatively large unbalance conditions.

A CFD Based Approach for Estimation of Rotor Dynamic Coefficients for Liquid Annular Seals in Turbomachinery

2018 ◽  
Author(s):  
Bachanti Krishna ◽  
B. Premachandran ◽  
Ashish K. Darpe
Keyword(s):  
High Speed ◽  
Reaction Force ◽  
Physical And Mechanical Properties ◽  
Working Fluid ◽  
Complex Geometries ◽  
Experimental Conditions ◽  
Rotordynamic Coefficients ◽  
Dynamic Coefficients ◽  
Rotor Dynamic ◽  
Annular Seals

Seals are used to control leakage across stages in pumps and other rotating machinery such as turbomachines. However, while acting to control leakage, the seals generate a reaction force on the rotating members. The rotordynamic forces produced by fluid impact the stability behaviour of the high-speed turbomachinery, therefore precise estimation of rotordynamic parameters is important to ensure vibrational stability and desired dynamic performance of rotors having annular seals. Studies on seals have so far mainly focused on bulk flow model based on Hirs turbulent lubrication theory for calculating leakage flow rate and rotordynamic coefficients. However, it is incapable to deal complex geometries and is less efficient in predicting precise rotor dynamic parameters for high speed rotating systems due to its basic assumptions. The experiments performed for calculating rotordynamic coefficients show their dependence on many physical and mechanical properties such as working fluid properties, pressure drop, seal clearance, rotor speed, eccentricity and misalignments. With the latest high performance computing facilities it is now relatively easy to simulate the flow in seal and evaluate the dynamic coefficients at high rotational speeds and with complex geometries. This paper proposes a 3-D CFD based transient stimulation method to capture the experimental conditions in virtual environment. The fluid force is calculated by integrating pressure to the rotor surface and the stiffness and damping coefficients are evaluated by appropriate curve fitting of fluid forces for various eccentricity values. The coefficients obtained from the present method show better correlation with experimental data compared to the existing steady state CFD and theoretical models. Variation of these rotordynamic coefficients with eccentricity helps in assessing the safe design of turbomachinery.

Modeling of Oil-Film Forces in Squeeze-Film Bearings

1986 ◽  
Vol 108 (2) ◽  
pp. 262-269 ◽  
Author(s):  
C. R. Burrows ◽  
M. N. Sahinkaya ◽  
N. C. Kucuk
Keyword(s):  
Parameter Estimation ◽  
System Performance ◽  
Critical Speed ◽  
Nonlinear Models ◽  
Squeeze Film ◽  
Model Structure ◽  
Oil Film ◽  
Model Oil ◽  
Stiffness And Damping ◽  
Parameter Estimation Techniques

The role played by bearings in determining the dynamic characteristics of rotor-bearing systems is well known. This has led to various attempts to model oil-film force coefficients in terms of linearized stiffness and damping elements. The inadequacy of these theoretical coefficients to predict performance under certain conditions has led some authors to propose the use of nonlinear models. An alternative philosophy, developed in this paper, is to retain a linear model structure and seek to determine optimized coefficient values using modern parameter estimation techniques. It is shown that these estimated linearized parameters predict system performance more accurately than the theoretical linear coefficients; particularly when the rotor is operating near a critical speed.

Evaluation of Pivot Stiffness for Typical Tilting-Pad Journal Bearing Designs

1988 ◽  
Vol 110 (2) ◽  
pp. 165-171 ◽  
Author(s):  
R. G. Kirk ◽  
S. W. Reedy
Keyword(s):  
High Speed ◽  
Fluid Film ◽  
Hertzian Contact ◽  
Tilting Pad ◽  
Hertzian Contact Stress ◽  
Bearing Stiffness ◽  
Stress And Deformation ◽  
The Individual ◽  
Stiffness And Damping ◽  
Tilting Pad Journal Bearing

The manufacturers of high speed turbomachinery are concerned with the accurate prediction of rotor response and stability. One major factor in the placement of system critical speeds and amplification factors is the stiffness and damping of both the fluid-film bearing and support structure. Typical calculated results for tilting-pad fluid-film bearings have neglected the influence of the point or line contact of the pivot support for the individual pads. This paper will review the equations developed considering the Hertzian contact stress and deformation theory and present the equations for pivot stiffness necessary for inclusion in tilting pad bearing computer programs. In addition, the influence of various standard pivot designs will be compared for typical fluid-film bearing stiffness and damping characteristics.

Effects of Turbulence and Viscosity Variation on the Dynamic Coefficients of Fluid Film Journal Bearings

1985 ◽  
Vol 107 (2) ◽  
pp. 256-261 ◽  
Author(s):  
D. F. Wilcock ◽  
O. Pinkus
Keyword(s):  
High Speed ◽  
Dynamic Stiffness ◽  
Journal Bearings ◽  
Fluid Film ◽  
Turbulent Regime ◽  
Dynamic Coefficients ◽  
Damping Characteristics ◽  
Fluid Film Bearings ◽  
Viscosity Variation ◽  
Stiffness And Damping

Many high-speed or large fluid film bearings operate in the turbulent regime. However, relatively little consideration has been given to the effects of turbulence and of the variation in viscosity on the dynamic stiffness and damping characteristics of the bearings. Since the dynamic behavior of the rotor supported on such bearings is often closely tied to the bearing dynamic coefficients, knowledge of them may be critical to both the design and the in-place correction of rotor instabilities. These effects are here considered in some detail on the basis of computer calculated analytical results, both in general dimensionless terms and with regard to a specific numerical example.

The Influence of Pad Flexibility on the Dynamic Coefficients of a Tilting Pad Journal Bearing

1987 ◽  
Vol 109 (1) ◽  
pp. 65-70 ◽  
Author(s):  
Jorgen W. Lund ◽  
Lars Bo Pedersen
Keyword(s):  
Approximate Method ◽  
Small Amplitude ◽  
Journal Bearing ◽  
Damping Properties ◽  
Dynamic Coefficients ◽  
Tilting Pad ◽  
Hydrodynamic Solution ◽  
Stiffness And Damping ◽  
Tilting Pad Journal Bearing ◽  
Good Agreement

An approximate method is developed to include the flexibility of the pad in the calculation of the stiffness and damping properties of a tilting pad journal bearing. It is a small-amplitude perturbation solution in which the pad deformation is accounted for solely by the change in clearance. A comparison of results with those obtained from a more complete elasto-hydrodynamic solution shows good agreement.

Dynamic Coefficients of Axial Spline Couplings in High-Speed Rotating Machinery

1994 ◽  
Vol 116 (3) ◽  
pp. 250-256 ◽  
Author(s):  
C. P. Roger Ku ◽  
J. F. Walton ◽  
J. W. Lund
Keyword(s):  
High Speed ◽  
Experimental Measurements ◽  
Viscous Damping ◽  
Bending Moments ◽  
Equivalent Viscous Damping ◽  
Damping Coefficients ◽  
Dynamic Coefficients ◽  
Test Conditions ◽  
Spline Coupling ◽  
Stiffness And Damping

This paper provided the first opportunity to quantify the angular stiffness and equivalent viscous damping coefficients of an axial spline coupling used in highspeed turbomachinery. The bending moments and angular deflections transmitted across an axial spline coupling were measured while a nonrotating shaft was excited by an external shaker. A rotordynamics computer program was used to simulate the test conditions and to correlate the angular stiffness and damping coefficients. The effects of external force and frequency were also investigated. The angular stiffness and damping coefficients were used to perform a linear steady-state rotordynamics stability analysis, and the unstable natural frequency was calculated and compared to the experimental measurements.

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