Effect of Scratches on a Tilting-Pad Journal Bearing

Abstract Many industrial rotating machines are equipped with hydrodynamic journal bearings, such as centrifugal compressors, steam turbines, pumps and motors. After some time from the installation, however, the surface of the bearings often presents imperfections and slight damages mainly caused by the presence of harder particles in the lubricant during start-ups and shut-downs, when the hydrodynamic mechanism is not well developed and the mixed lubrication can occur. The presence of scratches on a bearing can lead to variations of the oil film thickness which, in turn, causes significant degradation of the bearing hydrodynamic performance. For example, the reduction of the minimum oil-film thickness can lead to the increase in the local temperature, to local pressure peaks and, finally, to the failure of the bearing. Experimental data relating to scratches on journal bearings are extremely limited in the literature especially for tilting-pad journal bearings (TPJBs). An experimental activity was carried out to study the effect of artificial scratches on pads on the static and dynamic behaviors of a TPJB. The number of scratches, the depth and the axial position have been investigated and the dynamic coefficients have been estimated as well. The experimental results confirmed a degradation of the dynamic performance of the bearing in case of scratches, that it has has been also confirmed by means of numerical simulations.

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The Rolling-Pad Journal Bearing: A Promising Antiwhirl Configuration

Journal of Mechanical Engineering Science ◽

10.1243/jmes_jour_1981_023_026_02 ◽

1981 ◽

Vol 23 (3) ◽

pp. 131-141

Author(s):

M. Malik ◽

R. Sinhasan ◽

D. V. Singh

Keyword(s):

Journal Bearing ◽

Dynamic Performance ◽

Journal Bearings ◽

Operating Conditions ◽

Performance Characteristics ◽

Tilting Pad ◽

The Comparative Study ◽

Tilting Pad Journal Bearing ◽

Tilting Pad Journal Bearings ◽

Theoretical Performance

The rolling-pad journal bearing is a kinematic variation of the well-known tilting-pad journal bearing. In rolling-pad bearings, the pads, instead of tilting about fixed pivots, roll at their back surfaces on the inside surface of a common sleeve to accommodate changes in the operating conditions of the bearing. This paper presents a comparison of the theoretical performance characteristics of rolling-pad journal bearings with those of tilting-pad journal bearings. The comparative study indicates that the dynamic performance characteristics of the rolling-pad bearing configuration are superior to those of the tilting-pad bearing.

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Characterization of Five-Pad Tilting-Pad Journal Bearings Using an Original Test-Rig

Volume 1: 23rd Biennial Conference on Mechanical Vibration and Noise, Parts A and B ◽

10.1115/detc2011-48166 ◽

2011 ◽

Author(s):

S. Chatterton ◽

P. Pennacchi ◽

A. Vania ◽

E. Tanzi ◽

R. Ricci

Keyword(s):

Film Thickness ◽

Gas Turbines ◽

Journal Bearings ◽

Fluid Film ◽

Test Rig ◽

Theoretical Evaluation ◽

Oil Film ◽

Tilting Pad ◽

Fluid Film Thickness ◽

Tilting Pad Journal Bearings

Tilting-pad journal bearings are installed with increased frequency owing to their dynamic stability characteristics in several rotating machine applications, typically in high rotating speed cases. This usually happens for new installations in highspeed compressors or during revamping operations of steam and gas turbines for power generation. The selection from a catalogue, or the design of a new bearing, requires the knowledge of the bearing characteristics such as babbitt metal temperatures, fluid-film thickness, load capacity, stiffness and damping coefficients. Temperature and fluid-film thickness are essential for the safety of the bearing. Babbitt metal is subject to creep at high temperatures, as it happens at high speed operations. On the contrary, at low speed or with high loads, oil-film thickness could be too low, resulting in metal to metal contact. Oil-film dynamic coefficients are largely responsible of the dynamic behaviour and of the stability of the rotor-tilting-pad-bearing system. Therefore, the theoretical evaluation and/or the experimental estimation of these coefficients are mandatory in the design phase. The theoretical evaluation of these coefficients for tilting pad journal bearings is difficult due to their complex geometry, boundary and thermal conditions and turbulent flow, whereas an experimental characterization requires a suitable test rig. The paper describes the test rig designed to this purpose and its unusual configuration with respect to other test rigs available in literature. Some preliminary tests performed for the bearing characterization are also shown.

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On the Simplifications for the Thermal Modeling of Tilting-Pad Journal Bearings Under Thermoelastohydrodynamic Regime

Volume 7: Structures and Dynamics, Parts A and B ◽

10.1115/gt2012-68329 ◽

2012 ◽

Cited By ~ 5

Author(s):

Alejandro Cerda Varela ◽

Michel Fillon ◽

Ilmar Ferreira Santos

Keyword(s):

Heat Transfer ◽

Journal Bearing ◽

Journal Bearings ◽

Laminar Regime ◽

Transfer Effects ◽

Oil Film ◽

Tilting Pad ◽

Heat Transfer Effects ◽

Tilting Pad Journal Bearing ◽

Tilting Pad Journal Bearings

The relevance of calculating accurately the oil film temperature build up when modeling tilting-pad journal bearings is well established within the literature on the subject. This work studies the feasibility of using a thermal model for the tilting-pad journal bearing which includes a simplified formulation for inclusion of the heat transfer effects between oil film and pad surface. Such simplified approach becomes necessary when modeling the behavior of tilting-pad journal bearings operating on controllable lubrication regime. Three different simplified heat transfer models are tested, by comparing their results against the ones obtained from an state of the art tilting-pad journal bearing model, where the heat transfer effects are throughly implemented, as well as against some experimental results from the literature. The results obtained show that the validity of the simplified heat transfer models are strongly dependent on the Reynolds number for the oil flow in the bearing. For bearings operating in laminar regime, the decoupling of the oil film energy equation solving procedure, with no heat transfer terms included, with the pad heat conduction problem, where the oil film temperature is applied at the boundary as a Dirichlet condition, showed a good balance between quality of the results, implementation easiness and reduction in calculation time. For bearings on the upper limit of the laminar regime, the calculation of an approximated oil film temperature gradient in the radial direction, as proposed by Knight and Barrett, delivered the best results.

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

Volume 9: Mechanics of Solids, Structures and Fluids; NDE, Structural Health Monitoring and Prognosis ◽

10.1115/imece2017-70464 ◽

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.

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Dynamic Analysis of Tilting-Pad Journal Bearing—Influence of Pad Deformations

Journal of Tribology ◽

10.1115/1.2928890 ◽

1994 ◽

Vol 116 (3) ◽

pp. 621-627 ◽

Cited By ~ 25

Author(s):

H. Desbordes ◽

M. Fillon ◽

C. Chan Hew Wai ◽

J. Frene

Keyword(s):

Film Thickness ◽

Pressure Field ◽

Journal Bearing ◽

Maximum Pressure ◽

Tilting Pad ◽

Minimum Film Thickness ◽

Dimensional Finite Element ◽

The One ◽

Tilting Pad Journal Bearing ◽

Tilting Pad Journal Bearings

A theoretical nonlinear analysis of tilting-pad journal bearings is presented for small and large unbalance loads under isothermal conditions. The radial displacements of internal pad surface due to pressure field are determined by a two-dimensional finite element method in order to define the actual film thickness. The influence of pad deformations on the journal orbit, on the minimum film thickness and on the maximum pressure is studied. The effects of pad displacements are to decrease the minimum film thickness and to increase the maximum pressure. The orbit amplitude is also increased by 20 percent for the large unbalance load compared to the one obtained for rigid pad.

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Numerical Investigation for Characteristics and Oil-Air Distributions of a Tilting-Pad Journal Bearing Under Different Loads

Volume 10A: Structures and Dynamics ◽

10.1115/gt2020-15151 ◽

2020 ◽

Author(s):

Aoshuang Ding ◽

Xuesong Li

Keyword(s):

Film Thickness ◽

Journal Bearing ◽

Viscosity Ratio ◽

Cavitation Model ◽

Tilting Pad ◽

Sst Model ◽

Bearing Load ◽

Simulation Results ◽

Bearing Loads ◽

Tilting Pad Journal Bearing

Abstract This paper analyses the flow characteristics and oil-air distributions of oil flows in a tilting-pad journal bearing under different bearing loads. This titling-pad journal bearing is working at 3000 rpm rotation speed and its minimum film thicknesses have been measured under different loads from 180 kN to 299 kN. Based on the previous researches of this bearing under 180 kN, the gaseous cavitation and low-turbulence flow exists in this bearing flow. A suitable gaseous cavitation model and the SST model with low-Re correction are used in the film flow simulations. With the rotor and pads assumed to be rigid, the dynamic mesh and motion equations are applied to simulate the motions of the rotor and the rotations of the pads. Based on the simulation results under different bearing loads, the simulated minimum film thicknesses agrees well with the measured data. It indicates that the simulation results can catch the film geometries and flows correctly. With the load increasing, the rotor moves closer to the loaded pads and the minimum film thickness decreases. Taking the effect of boundary layers into consideration, the turbulence has a negative relationship with the film thickness and decreases in the loaded area under higher bearing load. It can be verified by the simulated lower turbulent viscosity ratio distributions in the loaded pads. In the unloaded area, both the film thickness and turbulence viscosity ratio are positively related to the bearing loads. Thus, the higher bearing load may lead the flow to be more different in the loaded and unloaded area, and the turbulence in the loaded pads may transfer to laminar in the end. As for the oil-air distributions, in the unloaded pads, with the bearing load increasing, the simulated air volume fraction increases in the unloaded pads with lower pressure. It should be caused by the higher film thickness of the unloaded pads under higher loads. In sum, the flow turbulence and cavitation process changes with the bearing load. With a higher load, the cavitation becomes more in the unloaded pads and the flow changes sharper from the high-turbulence unloaded area to the low-turbulence loaded area. As the simulation results is in good accordance with the experimental data, the SST model with low-Re correction and the gaseous cavitation model are verified to be suitable for bearing film simulations under different loads.

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Cooled Pads for Tilting-Pad Journal Bearings

Lubricants ◽

10.3390/lubricants7100092 ◽

2019 ◽

Vol 7 (10) ◽

pp. 92

Author(s):

Steven Chatterton ◽

Paolo Pennacchi ◽

Andrea Vania ◽

Phuoc Vinh Dang

Keyword(s):

Cross Sections ◽

Three Dimensional ◽

Experimental Tests ◽

Journal Bearings ◽

Maximum Temperature ◽

Inlet Temperature ◽

Oil Film ◽

External Cooling ◽

Tilting Pad ◽

Tilting Pad Journal Bearings

Tilting-pad journal bearings (TPJBs) are widely installed in rotating machines owing to their high stability, but some drawbacks can be noted, such as higher cost with respect to cylindrical journal bearings and thermal issues. High temperatures in the pads correspond to low oil-film thicknesses and large thermal deformations in the pads. Therefore, the restriction of the maximum temperature of the bearing is a key aspect for oil-film bearings. The temperature reduction is generally obtained by adopting higher oil inlet flowrates or suitable oil nozzles. In this paper, the idea of using cooled pads with internal channels in which an external cooling fluid is circulated will be applied to a TPJB for the first time. The three-dimensional TEHD model of the TPJB, equipped with a cooled pad, will be introduced, and the results of the numerical simulations will be discussed. Several analyses have been performed in order to investigate the influence of cooling conditions, such as the type, flowrate, inlet temperature and number of cooled pads. Two types of pad geometry with different cross-sections of the cooling circuit, namely, circular and six-square multi-channel sections, have been compared to the reference bearing with solid pads. Simple experimental tests were performed by means of a test rig equipped with a cooled pad bearing obtained with the additive manufacturing process, thus showing the effectiveness of the solution and the agreement with the predictions.

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