Axial Oil Film Rupture in High Speed Bearings Due to the Effect of the Centrifugal Force

1995 ◽  
Vol 117 (3) ◽  
pp. 394-398 ◽  
Author(s):  
Carlos E. Koeneke ◽  
Masato Tanaka ◽  
Hisayuki Motoi
Keyword(s):  
Centrifugal Force ◽  
High Speed ◽  
Axial Direction ◽  
Lubricant Film ◽  
Navier Stokes ◽  
Film Rupture ◽  
Navier Stokes Equation ◽  
High Rotational Speed ◽  
Lubricating Film ◽  
Very High

The two-dimensional steady-state Navier-Stokes equation and the continuity equation are applied to the lubricating film assumed to be concentric in journal bearings operating at very high speeds. The equations are numerically solved for the pressure variation in the axial direction and also across the film thickness with the centrifugal force being considered to act on the lubricant film due to high rotational speed of the journal. Linked with a new cavitation model proposed, the lubricant film is theoretically found to rupture near the journal surface toward the bearing end. This axial film rupture (AFR) is shown to reduce the driving torque of the inner film of floating bush bearings at very high shaft speeds, and some phenomena observed in the operation of floating bush bearings can be explained with this model.

Quantitative Analysis of Reynolds and Navier–Stokes Based Modeling Approaches for Isothermal Newtonian Elastohydrodynamic Lubrication

2021 ◽  
Vol 143 (12) ◽  
Author(s):  
Leoluca Scurria ◽  
Tommaso Tamarozzi ◽  
Oleg Voronkov ◽  
Dieter Fauconnier
Keyword(s):  
High Speed ◽  
Stokes Equations ◽  
Thickness Distribution ◽  
Elastohydrodynamic Lubrication ◽  
Lubricant Film ◽  
Secondary Flows ◽  
Navier Stokes ◽  
Shear Stresses ◽  
Low Viscosity ◽  
Fluid Film Thickness

Abstract When simulating elastohydrodynamic lubrication, two main approaches are usually followed to predict the pressure and fluid film thickness distribution throughout the contact. The conventional approach relies on the Reynolds equation to describe the thin lubricant film, which is coupled to a Boussinesq description of the linear elastic deformation of the solids. A more accurate, yet a time-consuming method is the use of computational fluid dynamics in which the Navier–Stokes equations describe the flow of the thin lubricant film, coupled to a finite element solver for the description of the local contact deformation. This investigation aims at assessing both methods for different lubrication conditions in different elastohydrodynamic lubrication (EHL) regimes and quantify their differences to understand advantages and limitations of both methods. This investigation shows how the results from both approaches deviate for three scenarios: (1) inertial contributions (Re > 1), i.e., thick films, high speed, and low viscosity; (2) high shear stresses leading to secondary flows; and (3) large deformations of the solids leading to inaccuracies of the Boussinesq equation.

Unsteady Flow at the Outlet of the High Specific Speed Centrifugal Compressor Impeller

1984 ◽  
Author(s):  
Fumikata Kano ◽  
Takafumi Shirakami
Keyword(s):  
Unsteady Flow ◽  
Centrifugal Compressor ◽  
Coal Gasification ◽  
Three Dimensional ◽  
Axial Direction ◽  
Navier Stokes ◽  
Meridional Plane ◽  
Mixed Flow ◽  
Navier Stokes Equation ◽  
Specific Speed

The unsteady flow at the outlet of the high specific speed mixed flow Impeller was studied. The specific speed is 500 (m3/min)1/2 · rpm · m−3/4. The flow is strongly influenced by the impeller blading. The other hand, the flow influences the performance of the stationary vanes downstream of the impeller. The flow path at the outlet of the mixed flow impeller is inclined to the axial direction and is curved in the meridional plane. The study was carried out to develop the 30 MW centrifugal compressor. This compressor is used in the field of the coal gasification, the geothermal power generation, etc. The distributions of flow velocity, pressure and temperature of three dimensional flow were measured using a high sensitive pressure transducer and a total temperature probe. The flow was surveyed across the entire passage at about ten axial locations including endwall boundary layer. A theoretical analysis was also carried out using the linearized Navier-Stokes equation.

scholarly journals A HIGH SPEED VACUUM CENTRIFUGE SUITABLE FOR THE STUDY OF FILTERABLE VIRUSES

1936 ◽  
Vol 64 (4) ◽  
pp. 503-528 ◽  
Author(s):  
Johannes H. Bauer ◽  
Edward G. Pickels
Keyword(s):  
Centrifugal Force ◽  
Yellow Fever ◽  
High Speed ◽  
Yellow Fever Virus ◽  
High Vacuum ◽  
Fever Virus ◽  
Compressed Air ◽  
Frictional Heat ◽  
High Speeds ◽  
Very High

1. A high speed centrifuge is described in which the speed is limited only by the strength of the material of which the rotor is made. It carries sixteen tubes, each of which conveniently accommodates 7 cc. of fluid. 2. The centrifuge operates in a very high vacuum and therefore requires only a small amount of driving energy. The arrangement has been found to eliminate the possibility of producing injurious frictional heat. 3. The rotating parts are supported by anair-bearing and are driven by compressed air. 4. The centrifuge has been successfully operated at a speed of 30,000 revolutions per minute, representing a maximum centrifugal force in the fluid of 95,000 times gravity. 5 Celluloid tubes used for centrifugation of fluid at high speeds are described. 6. Experiments are described in which good sedimentation of the yellow fever virus was obtained.

The Effect of Centrifugal Stretching in High-Speed, Self-Acting Gas Bearings Operating under Steady-State Conditions

1974 ◽  
Vol 16 (3) ◽  
pp. 139-146
Author(s):  
K. S. H. Sadek ◽  
B. N. Cole ◽  
D. Dowson
Keyword(s):  
Radial Growth ◽  
High Speed ◽  
Load Carrying Capacity ◽  
Gas Bearings ◽  
Rotary Machine ◽  
Lubricating Film ◽  
Pressure Distributions ◽  
High Speeds ◽  
Load Carrying ◽  
Very High

The study reported in this paper arose from an investigation of methods of achieving oil-free compression of refrigerant vapours. One part of the investigation included a feasibility study of a high-speed rotary machine running in self-acting gas bearings lubricated by the refrigerant. In certain designs of very high-speed rotor-bearing arrangements, centrifugal or radial growth of the journal might disturb the shape and magnitude of the nominal clearance space and thus affect the performance characteristics of the bearing. The nature and magnitude of these changes in bearing performance for uniform and for two forms of non-uniform centrifugal growth have been examined theoretically. Typical gas-film pressure distributions are presented together with design charts showing how attitude angle and load carrying capacity vary with speed. Comparisons are made with the performance of bearings having the same eccentricity ratio on the mid-plane, and guidance is given on the calculation of uniform radial growth at high speeds. It is concluded that changes in lubricating film geometry resulting from centrigual stretching might have a significant effect upon the performance of certain high-speed, self-acting gas-lubricated bearings.

scholarly journals Thermo-Elastohydrodynamic Study on Textured Journal Bearing with High-Speed and High-Specific-Pressure

2019 ◽  
Vol 37 (4) ◽  
pp. 751-756 ◽  
Author(s):  
Lin Wang ◽  
Yu Zhang ◽  
Guoding Chen
Keyword(s):  
Elastic Deformation ◽  
High Speed ◽  
Journal Bearing ◽  
Hydrodynamic Performance ◽  
Navier Stokes ◽  
Specific Pressure ◽  
Analysis Model ◽  
Navier Stokes Equation ◽  
Gear Transmission System ◽  
Load Carrying

The performance of supporting journal bearing of the star gear transmission system in the geared turbo fan engine (GTF) is analyzed. A thermal-elastohydrodynamic analysis model was developed for textured journal bearing used in high-speed and high-specific-pressure conditions. The Navier-Stokes equation, energy equation, and viscosity-temperature equation were calculated by the computational fluid dynamics method. The influence of elastic deformation on bearing thermal hydrodynamic performance was studied in detail. The results indicate that the elastic deformation has an influence on the distribution of oil temperature and oil pressure. Besides, a comparative thermo-elastohydrodynamic analysis was conducted between the textured bearing and the un-textured bearing, and the discrepancies of maximum oil pressure, load carrying capacity and the maximum oil temperature are few. However, the textured bearing has a lower elastic deformation than the un-textured bearing.

A Transient CFD Simulation of the Flow in a Test Rig of an Aeroengine Bearing Chamber

2014 ◽  
Author(s):  
Akinola A. Adeniyi ◽  
Hervé P. Morvan ◽  
Kathy A. Simmons
Keyword(s):  
High Speed ◽  
Cfd Simulation ◽  
Film Formation ◽  
Navier Stokes ◽  
Navier Stokes Equation ◽  
Oil Film ◽  
Sheared Flow ◽  
Fine Mesh ◽  
Computational Overhead ◽  
Formation Pattern

In this paper, we present results for the application of an Eulerian-Lagrangian technique to the transient simulation of an oil film formation on the walls of an aeroengine bearing chamber. The flow of oil in an aeroengine bearing chamber consists of high speed oil droplets interacting with the bearing structures and flowing oil film. The situation in the chamber is highly rotational and consisting of sheared flow of air over oil. The bearing chamber may also be located in the vicinity of the combustion chamber. The oil provides lubrication and cooling of the hot structures. Modelling the flow in the bearing chamber is therefore complex. The Volume of Fluid (VoF) technique offers a potential platform to model droplet-film interaction; however, it requires fine mesh details to capture the flow to the droplet level. Such detailed resolution would not be practical for the complete chamber geometry because of the prohibitively expensive computational overhead requirements. A Lagrangian formulation is therefore proposed to represent the droplets as source terms in the Navier-Stokes equation while the film is represented using VoF. This effectively reduces the need to resolve the droplets explicitly. The predicted film formation pattern compares with experimental results.

scholarly journals On lower-dimensional models in lubrication, Part A: Common misinterpretations and incorrect usage of the Reynolds equation

2020 ◽  
pp. 135065012097379
Author(s):  
Andreas Almqvist ◽  
Evgeniya Burtseva ◽  
Kumbakonam Rajagopal ◽  
Peter Wall
Keyword(s):  
Stokes Equation ◽  
Reynolds Equation ◽  
Elastohydrodynamic Lubrication ◽  
Lubricant Film ◽  
The Body ◽  
Navier Stokes ◽  
Navier Stokes Equation ◽  
Constant Viscosity ◽  
Incompressible Navier Stokes Equation ◽  
Lower Dimensional

Most of the problems in lubrication are studied within the context of Reynolds’ equation, which can be derived by writing the incompressible Navier-Stokes equation in a dimensionless form and neglecting terms which are small under the assumption that the lubricant film is very thin. Unfortunately, the Reynolds equation is often used even though the basic assumptions under which it is derived are not satisfied. One example is in the mathematical modelling of elastohydrodynamic lubrication (EHL). In the EHL regime, the pressure is so high that the viscosity changes by several orders of magnitude. This is taken into account by just replacing the constant viscosity in either the incompressible Navier-Stokes equation or the Reynolds equation by a viscosity-pressure relation. However, there are no available rigorous arguments which justify such an assumption. The main purpose of this two-part work is to investigate if such arguments exist or not. In Part A, we formulate a generalised form of the Navier-Stokes equation for piezo-viscous incompressible fluids. By dimensional analysis of this equation we, thereafter, show that it is not possible to obtain the Reynolds equation, where the constant viscosity is replaced with a viscosity-pressure relation, by just neglecting terms which are small under the assumption that the lubricant film is very thin. The reason is that the lone assumption that the fluid film is very thin is not enough to neglect the terms, in the generalised Navier-Stokes equation, which are related to the body forces and the inertia. However, we analysed the coefficients in front of these (remaining) terms and provided arguments for when they may be neglected. In Part B, we present an alternative method to derive a lower-dimensional model, which is based on asymptotic analysis of the generalised Navier-Stokes equation as the film thickness goes to zero.

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