Bearing Chamber Research Articles

The study of droplet deformation and droplet volume fraction in an aero-engine bearing chamber

Inside an aero-engine bearing chamber, the shape, velocity, and temperature of each droplet shed from roller elements keep changing under the actions of the rotating airflow. Research on droplet deformation, droplet motion, and droplet volume fraction is fundamental to the understanding of the complex two-phase flow in an aero-engine bearing chamber. In this paper, the modified Taylor analogy breakup model, equations of temperature and motion are established to obtain the size, temperature, and velocity of a deformed droplet. Subsequently, a method is presented to solve for the droplet volume fraction in a bearing chamber based on the size and motion parameters of deformed droplets. In the end, a simplified bearing chamber experimental setup has been constructed. Comparisons between the experimental results and theoretical calculations show a good match based upon the research analogy used. The research work in this paper can provide theoretical foundations for the analyses of heat exchange and lubrication in bearing chambers. This also has great significance in realizing the rigorous design required for the lubrication system of an aero-engine.

Numerical Study on the Improvement of Oil Return Structure in Aero-Engine Bearing Chambers

Abstract Numerical study has been carried out to improve the unreasonable oil film accumulation and oil return effect of the bearing chamber. Ramp sump and eccentricity sump offtake structures are designed and improved, and oil-gas two-phase flow calculation model based on CLSVOF (coupled level set and volume of fluid) method is proposed. Based on the grid-independent analysis and verifying the rationality of numerical data, oil-gas movement mechanism and oil return characteristics for different scavenge offtakes are calculated and analyzed. Results show that both the ramp sump and eccentricity sump offtake structures have favorable effects on improving the local oil distribution such as recirculation and stripping, etc. at low rotation speeds and alleviating the rapid decline of scavenge efficiency at high rotation speeds. Meanwhile, the air shear force is the main reason for the rapid decline of scavenge efficiency, while the design of oil return sump makes for the oil discharge from the scavenge offtake, and the deeper the sump depth is, the better.

Transient Thermal Modeling of Ball Bearing Using Finite Element Method

Gas turbines are fitted with rolling element bearings, which transfer loads and supports the shafts. The interaction between the rotating and stationary parts in the bearing causes a conversion of some of the power into heat, influencing the thermal behavior of the entire bearing chamber. To improve thermal modeling of bearing chambers, this work focused on modeling of the heat generated and dissipated around the bearings, in terms of magnitude and location, and the interaction with the components/systems in the bearing chamber. A thermal network (TN) model and a finite element (FE) model of an experimental high-pressure shaft ball bearing and housing were generated and a comparison to test rig results have been conducted. Nevertheless, the purpose of the thermal matching process that focused on the FE model and experimental data is to provide a template for predicting temperatures and heat transfers for other bearing models. The result of the analysis shows that the predictions of the TN are considerate, despite the simplifications. However, lower relative errors were obtained in the FE model compared to the TN model. For both methods, the highest relative error is seen to occur during transient (acceleration and deceleration). This observation highlights the importance of boundary conditions and definitions: surrounding temperatures, heat split and the oil flow, influencing both the heat transfer and heat generation. These aspects, incorporated in the modeling and benchmarked with experimental data, can help facilitate other related cases where there is limited or no experimental data for validation.

Ejector Application for Scavenging of an Aero Engine Bearing Chamber

Oil system architecture in aero engines has remained almost the same for the last 35 years. At least one mechanically-driven oil feed pump is responsible for distributing pressurized oil into the bearing chambers and several scavenge pumps, also mechanically driven, are responsible for evacuating the bearing chambers from the oil and air mixture. Air is used as the sealing medium in bearing chambers and is the dominant medium in terms of volume occupation and expansion phenomena. In order to simplify the oil system architecture, improve the system's reliability with less mechanical parts, and also decrease weight, an ejector system has been designed for scavenging bearing chambers. In Flouros et al. (2013, “Ejector Scavenging of Bearing Chambers. A Numerical and Experimental Investigation,” ASME J. Eng. Gas Turbines Power, 135(8), p. 081602), an ejector system was presented which used aviation oil (MIL-PRF-23699 Std.) as the primary medium. In the course of further development, the original design was modified leading to a much smaller ejector. This ejector was tested in the rig using alternatively pressurized air or pressurized oil as primary medium. Additionally, three in-house developed primary nozzle (jet) designs were introduced and tested. The design of an ejector for application with compressible or incompressible media was supported through the development of an analysis tool. A momentum-based efficiency function is proposed herein and enables comparisons among different operating cases. Finally, ANSYS cfx (ANSYS, 2014, “ANSYS® CFX, Release 14.0,” ANSYS Inc., Canonsburg, PA) was used to carry out the numerical analysis. Similar to the ejector described in Flouros et al. (2013, “Ejector Scavenging of Bearing Chambers. A Numerical and Experimental Investigation,” ASME J. Eng. Gas Turbines Power, 135(8), p. 081602), the new design was also manufactured out of pure quartz glass to enable optical access. Through suitable instrumentation for pressures, temperatures, and air/oil flows, the performance characteristics of the new ejector were assessed and were compared to the analytic and numerical results. This work was partly funded by the German government within the research program Lufo4 (Luftfahrtforschungsprogramm 4/Aeronautical Research Program 4).

Influence of extrusion speed on the seam weld quality in the porthole die extrusion of AZ31 magnesium alloy tube

In the present work, an accurate 3D-FE model for simulating the extrusion process of AZ31 magnesium alloy tube was established based on the DEFORM 3D software package. The metal flow behavior and formation process of weld seam in the porthole die were revealed. The evolutions of temperature, velocity, and effective stress during the whole extrusion cycle were investigated. The K welding criteria was utilized to evaluate the influence of extrusion speed on the seam weld quality. Extrusion experiments were carried out at the extrusion speed ranging from 0.25 to 4 mm/s on an 800-t extrusion press. The simulation results show that the temperature distribution in the workpiece was not homogeneous. As the extrusion process proceeded, the greater the temperature gradient of workpiece was. The maximum temperature appeared at the bearing region. The dead metal zones existed at the corner between the container and the die face and between the bottom and the sidewall of welding chamber. The effective stress near the bearing and welding chamber was maximum, followed by the inlet ports of porthole die, and the minimum value was located in the container. As extrusion speed increased, the temperature, welding pressure, and effective stress on the welding plane increased simultaneously. The calculated K value decreased rapidly when extrusion speed increased from 0.5 to 2 mm/s and then reduced slowly when larger than 2 mm/s. Extrusion speed had a negative influence on the seam weld quality. The criteria exhibited a good predicting capability as compared with the experimental results. The optimum extrusion speed was about 0.5 mm/s for the extrusion of AZ31 magnesium alloy tube at the billet temperature of 400 °C on the 800-t extrusion press.

Transient Analysis of Air/Oil Two-Phase Flow in Bearing Chamber under the Periodic Boundary Conditions

The air/oil two-phase flow is extremely complex in the aero-engine bearing chamber, so the comprehensive understanding of the flow phenomenon is helpful to improve the design of the lubrication and heat exchange system. In this paper, transient CFD simulation is developed to analyse the air/oil two-phase flow in the bearing chamber. The velocity and temperature distributions of air and oil with time and space are discussed. The results show that under the periodic conditions, the velocity and temperature of the air and oil in the bearing chamber present quasi periodic characteristics. And the velocity and temperature distribution of air/oil two-phase flow in bearing chamber is independent with time in the bearing chamber. The research work will contribute to understand the nonlinear characteristics of air/oil two-phase flow in the bearing chamber.

Two-Phase Flow Pressure Drop in Corrugated Tubes Used in an Aero-engine Oil System

In modern aero-engines, the lubrication system holds a key role due to the demand for high reliability standards. An aero-engine bearing chamber contains components like bearings and gears. Oil is used for lubrication and for heat removal. In order to retain the oil in a bearing chamber, pressurized seals are used. These are pressurized using air from the compressor. In order to avoid overpressurization of the bearing chamber, air/oil passages are provided in the bearing chamber. At the top, a vent pipe discharges most of the sealing air and at the bottom, a scavenge pipe is used for discharging the oil by means of a pump (scavenge pump). The scavenge pipe is setup in most cases by tubes of circular or noncircular cross sections. When the scavenge pipe has to be routed in a way that sharp bends or elbows are unavoidable, flexible (corrugated) pipes can be used. Because of the corrugation, considerable flow resistance with high-pressure drop can result. This may cause overpressurization of the bearing compartment with oil loss into the turbomachinery with possibility of ignition, coking (carbon formation), or contamination of the aircraft’s air conditioning system. It is therefore important for the designer to be capable to predict the system’s pressure balance behavior. A real engine bearing chamber sealed by brush seals was used for generating different air/oil mixtures thus corresponding to different engine operating conditions. The mixtures were discharged through a scavenge pipe which was partly setup by corrugated tubes. Instead of a mechanical pump, an ejector was used for evacuating the bearing chamber. An extensive survey covering the existing technical literature on corrugated tube pressure drop was performed and is presented in this paper. The survey has covered both single-phase and multiphase flows. Existing methods were checked against the test results. The method which was most accurately predicting lean air test results from the rig was benchmarked and was used as the basis for extending into a two-phase flow pressure drop correlation by applying two-phase flow multiplier techniques similar to Lockhart and Martinelli. Comparisons of the new two-phase flow pressure drop correlation with an existing correlation by Shannak are presented for mixtures like air/oil, air/water, air/diesel, and air/kerosene. Finally, numerical analysis results using ansys cfx version 15 are presented.

Enhanced Computational Fluid Dynamics Modeling and Laser Doppler Anemometer Measurements for the Air-Flow in an Aero-engine Front Bearing Chamber—Part I

Modern aero-engine development requires also a gradual increase in the overall effectiveness of lubrication systems. This particularly applies to bearing chambers where a complex two-phase flow is formed by the interaction of the sealing air and the lubrication oil. It is important to increase the level of understanding of the flow field inside the bearing chamber and to develop engineering tools in order to optimize its design and improve its performance. To achieve this, an experimental and a computational study of the whole front bearing chamber were carried out for a range of shaft rotational speeds and sealing air mass flow. The experimental measurements of the air velocity inside the chamber were carried out using a laser Doppler anemometer (LDA) in two-phase air/oil-flow conditions. The experimental facility is a 1:1 scale model of the front bearing chamber of an aero-engine. Computational 3D modeling of the bearing chamber was performed. The bearing gap and the presence of lubrication oil were modeled as an anisotropic porous medium with functions relating the pressure loss of the air coming through the gap and the tangential component of velocity of the air exiting the gap of the ball bearing with the air-flow rate through the gap and the rotational speed of the shaft. The methodology to obtain the above mentioned functions and the results of the detailed study are given (Aidarinis, J., and Goulas, A., 2014, “Enhanced CFD Modeling and LDA Measurements for the Air-Flow in an Aero Engine Front Bearing Chamber: Part II,” ASME Paper No. GT2014-26062). The enhanced computational model of the chamber implementing the law of pressure drop of the “lubricated” bearing and the function of modeling the tangential velocity of the air exiting the bearing was used to calculate the flow field for the full range of the measurements. A limiting curve dividing the operational map of the bearing chamber into two areas was predicted. Large vortical and swirling structures dominate the flow and they vary in size according to the position of the operation point relative to the limiting curve. Operation above the limiting curve leads to flow classified as type I with air going through the ball bearing while for operation below the limiting curve line the flow is classified as type II, there is no air-flow through the bearing gap.

Enhanced Computational Fluid Dynamics Modeling and Laser Doppler Anemometer Measurements for the Air-Flow in an Aero-engine Front Bearing Chamber—Part II

A detailed computational study of the air-flow through the outer gap of the front bearing of an aero-engine is presented. The reason to carry out this study was to understand the flow through the bearing as a function of the operational parameters of the engine, which was necessary for the modeling of the flow in the whole bearing chamber. The complex geometry and the size of the bearing gap relative to the overall dimensions of the bearing chamber and the need for very precise and detailed information of the effect on the flow within the chamber of the bearing operational parameters, prohibited the solution of the flow through the gap together with the rest of the bearing chamber. A 3D modeling of the flow through the outer bearing gap, which included a section of the ball bearing, was performed. Functions relating the pressure drop of the air coming through the bearing gap and the tangential component of velocity of the air exiting the bearing region, to the mass of air through the gap of the ball bearing and the rotational speed of the shaft were developed. The effect of the lubrication oil within the bearing was modeled as an anisotropic porous medium with a predefined law. In order to acquire in a mathematical form the above relationships a series of computational runs were performed. These relationships, in the form of second order curves, were subsequently introduced to the model of the bearing chamber as described by Aidarinis and Goulas (2014, “Enhanced CFD Modeling and LDA Measurements for the Air-Flow in an Aero Engine Front Bearing Chamber (Part I),” ASME Paper No. GT2014-26060). The constants of the relationships were derived through comparisons of the calculations with the experimental data. From the analysis, it was concluded that the pressure drop across the bearing increases with the square of the rotational speed of the shaft with the mass flow of air through the ball bearing as a parameter and vice versa. For this particular ball bearing, there is a region where, for any combination of rotational speed of the shaft and pressure drop through the bearing, there is no flow of air through the bearing. In this paper the detailed modeling methodology, the computational flow field, the boundary conditions and finally the results are presented and discussed.

Effect of surface finishing, temperature and chemical ageing on the tribological behaviour of a polyether ether ketone composite/52100 pair

Polyether ether ketone (PEEK) composites and AISI 52100 steel are high-performance materials that are often selected for high stress tribological applications under solid and hydrodynamic lubrication. In this study, the viability of these materials as a pair for boundary-lubricated systems was evaluated. Tribo-tests to evaluate different characteristics were conducted: (i) the effect of metallic surface finish (1µm polished, 9µm polished, shot peened and ground); (ii) the effect of temperature (room temperature and 90°C); and (iii) the effect of long-term PEEK exposure to lubricant oil (i.e., chemical ageing). An AMTI tribometer equipped with a hermetic chamber and a heating system was used for reciprocating sliding tests with a 10mm stroke, 2Hz frequency and 2h duration. The tests used a cylinder-on-disc configuration (polymer on metal), a tetrafluoroethane atmosphere and a 100N normal force. The wear tracks were analysed using a light interferometer, SEM and optical microscope to assess the wear mechanisms, including transfer film formation. The surface skewness and transfer film establishment were the main factors affecting the friction coefficient. In contrast, the wear of the PEEK composites was mainly affected by the surface bearing index and chamber temperature. Moreover, transfer films were observed only on counterbodies that had a surface roughness (Sq) of at least 0.030µm. Finally, accelerated ageing of PEEK composites was performed in an autoclave at 180°C and 3bar pressure for 7 days in the presence of an ester-based lubricant oil and tetrafluoroethane atmosphere. DSC, DTG and FTIR techniques indicated that the filler/matrix interfaces of the PEEK composites were dissolved by the ester-based lubricant oil. Chemical ageing showed a significant effect on the friction steady state regime. Instead of a stable value, the friction coefficients of the aged composites increased slowly and continuously.

Numerical Modeling of Unsteady Oil Film Motion Characteristics in Bearing Chambers

AbstractTo obtain motion characteristics of the lubricating oil film on the aero-engine bearing chamber wall, a complete mathematical model based on theoretical study to solve three-dimensional unsteady oil film motion was established. On the basis of verifying the rationality of the computational model, the variations of the oil film thickness, velocity and temperature with the rotation speed and lubricating oil flow were analyzed and studied. The numerical results show that the following: In the stable oil film flow state, the oil film thickness shows a decreasing trend with increase in rotation speed and an increasing trend with increase in the lubricating oil flow. Particularly, comparison with the experimental work shows that the proposed numerical model based on theoretical study to solve unsteady oil film motion is a valuable technical means for the study of oil film movement mechanism and the design of actual bearing chamber.

Results of numerical modeling of two-phase liquid / gas flow on the basis of a simplifield model of oil chamber

Numerical simulation results of multiphase liquid/gas flow are presented. Calculation was preformed forsimplified bearing chamber. Work was kept within the framework of developing the methods of multiphase flows modeling in oil chambers of gas-turbine engine. At present there is no the instrument of the analysis, allowingto simulate the oil flow in oil systems, and oil chambers of gas-turbine engine. The tightening requirementsto mass, overall dimensions and performance of the engine need to reduce of the oil system sizes andamount of the oil, used for lubrication and cooling of bearing with increasing of their resource. At present, oilchamber design based on successful previous experience of the similar work, but performance of oil system ischecked only in process of the engine test. This problems in this case lead to significant time and financial expense,so this instrument of analysis allow simultaneously increase the bearing resource, reduce mass and size ofthe oil system. The most rational model of multiphase flow was also chosen and analysis of the mesh size influenceon steady calculation results was made.

Investigation of the Fluid-Solid Thermal Coupling for Rolling Bearing under Oil-Air Lubrication

An excellent oil-air lubrication system helps to improve rolling bearing's working conditions and thus extend its service life span. Flowing and heat dissipating characteristics of oil-air media inside bearing chamber are very complicated due to the fluid-solid thermal coupling. Effects of fluid-solid thermal coupling are neglected in all previous simulation efforts. A numerical model for simulating the flowing inside bearing chamber is developed here based on an analytical fluid-solid thermal coupling method under oil-air lubrication. The effects of the coupling of air-oil flowing and heat dissipating in bearing chamber are predicted. The simulation results indicate that the coupling is influential in the performances of the flowing in rolling bearing under oil-air lubrication. With consideration of the coupling, the turbulence intensity, the turbulent kinetic energy, and the temperature of the rollers are predicted to be lower because part of the heat is carried out by the flow due to the heat transfer. On the contrary, the turbulent dissipation rate gets higher when considering the coupling effects. It is also interesting that the coupling effects have little influence on the flow pressure and the velocity, which is manifested by a little higher predicted value when considering the coupling.

Thermal and Flow Phenomena Associated With the Behavior of Brush Seals in Aero Engine Bearing Chambers

Due to the increasing fuel cost and environmental targets, the demand for more efficient gas turbines has risen considerably in the last decade. One of the most important systems in a gas turbine is the secondary air system, which provides cooling air to the disks and to the blades. It also provides air for sealing of the bearing chambers. The amount of secondary air that is extracted from the compressor is a performance penalty for the engine. In aero engines, bearing chambers are in most cases sealed by the most traditional type of seal, the labyrinth seal. Bearing chambers contain the oil lubricated components like bearings and gears. In order to avoid oil migration from the bearing chamber into the turbomachinery, the seals are pressurized by secondary air; thus, a pressure difference is setup across the seal, which retains the lubricant into the bearing chamber. Oil loss can lead to a number of problems like oil fire or coking with the probability of an uncontained destruction of the aero engine. Oil fumes can also cause contamination of the air conditioning system of the aircraft thus cause discomfort to the passengers. Beside labyrinth seals, other types of seals such as brush seals and carbon seals are used. Both the latter are contact type seals, that is, they may be installed with zero gap and lift during operation when they get pressurized. Brush seals particularly may be installed having an overlap with the rotating part. An original aero engine bearing chamber was modified by MTU Aero Engines to run with brush seals in a simulating rig in Munich. Two types of brush seals were used for testing: (a) a brush seal with bristles made of Kevlar fibers and (b) a brush seal with bristles made of steel. Both types were installed with an overlap to the rotor. The targets set were twofold: (a) to measure the transient temperatures in the rotor and particularly in the contact zone between the bristles and the rotor and (b) to calculate the heat generation by the seals which could enable predictions of the heat generation in future applications (i.e., scaling to bigger rotor diameters). For the heat transfer calculations, numerical models using ansys cfx were created. Additionally, a coupled computational fluid dynamics (CFD) and finite element analysis (FEA) approach was applied to simulate flow and bristle's behavior. In order to obtain the transient temperature measurements with high fidelity, a new pyrometric technique was developed and was applied for the first time in brush seals as reported by Flouros et al. (2013, “Transient Temperature Measurements in the Contact Zone Between Brush Seals of Kevlar and Metallic Type for Bearing Chamber Sealing Using a Pyrometric Technique,” ASME J. Gas Turbines Power, 135(8), p. 081603) and Flouros et al. (2012, “Transient Temperature Measurements in the Contact Zone Between Brush Seals of Kevlar and Metallic Type for Bearing Chamber Sealing Using a Pyrometric Technique,” ASME Turbo Expo 2012, Copenhagen, Paper No. GT2012-68354). This technique has enabled positioning of the pyrometer (SensorthermGmbH, www.sensortherm.com) into the bristles pack of the seal adjacent to the rotating surface. The pyrometer could record the frictional temperature evolution in the bristles/rotor contact zone during accelerations or decelerations of the rotor. The sealing air demand can be reduced up to 97% with brush seals compared to traditional three fin labyrinth. It has been estimated that this can result in a reduction in fuel burned up to 1%. Further, the reduction in air flow has additional potential benefits such as a possible simplification of the bearing chamber architecture (vent less chamber). Even though the rotor was accelerated up to 19,500 rpm, the temperature induced overshoots in the seal/rotor contact zone have caused no deterioration in either the materials or the oil.

Two-Phase Flow Heat Transfer and Pressure Drop in Horizontal Scavenge Pipes in an Aero-engine

In modern aero-engines, the lubrication system plays a key role due to the demand for high reliability. Oil is used not only for the lubrication of bearings, gears, or seals but it also removes large amounts of the generated heat. Also, air from the compressor at elevated temperature is used for sealing the bearing chambers and additional heat is introduced into the oil through radiation, conduction, and convection from the surroundings. The impact of excessive heat on the oil may lead to severe engine safety and reliability problems which can range from oil coking (carbon formation) to oil fires. Coking may lead to a gradual blockage of the oil tubes and subsequently increase the internal bearing chamber pressure. As a consequence, oil may migrate through the seals into the turbomachinery and cause contamination of the cabin air or ignite and cause failure of the engine. It is therefore very important for the oil system designer to be capable to predict the system’s functionality. Coking or oil ignition may occur not only inside the bearing chamber but also in the oil pipes which carry away the air and oil mixture from the bearing chamber. Bearing chambers usually have one pipe (vent pipe) at the top of the chamber and also one pipe (scavenge pipe) at the bottom which is attached to a scavenge pump. The vent pipe enables most of the sealing air to escape thus avoid over-pressurization in the bearing compartment. In a bearing chamber, sealing air is the dominant medium in terms of volume occupation and also in terms of causing expansion phenomena. The scavenge pipe carries away most of the oil from the bearing chamber but some air is also carried away. The heat transfer in vent pipes was investigated by Busam (2004, “Druckverlust und Wärmeuebergang im Entlueftungssystem von Triebwerkslagerkammern (Pressure Drop and Heat Transfer in the Vent System in an Aero Engine’s Bearing Chamber),” Ph.D. thesis, Logos Verlag, Berlin, Germany) and Flouros (2009, “Analytical and Numerical Simulation of the Two Phase Flow Heat Transfer in the Vent and Scavenge Pipes of the CLEAN Engine Demonstrator,” ASME J. Turbomach., 132(1), p. 011008). Busam has experimentally developed a Nusselt number correlation for an annular flow in a vent pipe. For the heat transfer predictions in scavenge pipes, no particular Nusselt number correlation exist. This paper intends to close the gap in this area. As part of the European Union funded research programme ELUBSYS (Engine Lubrication System Technologies), an attempt was done to simplify the oil system’s architecture. In order to better understand the flow in scavenge pipes, high speed video was taken in two sections of the pipe (vertical and horizontal). In the vertical section, the flow was a wavy annular falling film, whereas the flow in the horizontal section was an unsteady wavy stratified/slug flow. Heat transfer has been investigated in the horizontal section of the scavenge pipe, leaving the investigation on the vertical section for later. Thanks to the provided extensive instrumentation, the thermal field in, on, and around the pipe was recorded, evaluated, and also numerically modeled using ansys cfx version 14. Brand new correlations for two-phase flow heat transfer (Nusselt number) and for pressure drop (friction coefficient) in horizontal scavenge pipes are the result of this work. The Nusselt number correlation has been developed in such a way that smooth transition (i.e., no discontinuity) from two-phase into single phase flow is observed.

Experimental Investigation Into the Efficiency of an Aero-engine Oil Jet Supply System

This paper presents results of investigations on the interaction between a targeted oil jet and a rotating shaft in an aero-engine typical bearing chamber. Measurements were performed at atmospheric temperature and pressure in order to study the influence of the operating conditions, nozzle diameters and impingement angles on the efficiency of such an oil supply system. The flow phenomena of the jet–shaft interaction were visualized. A qualitative analysis of the jet–shaft interaction revealed massive droplet generation due to the jet break-up in the air crossflow and its impact on the shaft. The latter could be reduced with shallower impingement angles. Measurements showed that the oil inflow rate, the shaft speed, and the nozzle diameter have a strong influence on the collected oil quantity, which is expressed as catch efficiency, i.e., the ratio of collected and supplied oil. The impingement angle was also identified to have a strong influence on the catch efficiency. The ratio of the momentum fluxes of supplied oil and chamber air flow is proposed as a parameter to correlate the catch efficiency to the operating conditions.

Application of the Ultrasonic Oil Film Thickness Measurement System in Bearing Chambers

The oil film thickness in aero-engine bearing chamber influences the heat transfer capacity of the bearing chamber wall, so measuring oil film thickness accuspeedly is essential to the design and thermal analysis of lubricating oil system. In this paper, software and hardware of an ultrasonic measurement system based on pulse echo technique, which measures the oil film thickness in bearing chamber, are established. The hardware system mainly consists of signal acquisition card, probe, delay block and the corresponding cables. Functions as measurement parameter setup, real-time display of measured waveforms, post-processing and so on are included in the measurement software. Finally, the oil film thickness of the wall is measured with the measurement system developed. Signal quality of the dynamic measurement is analyzed. Comparison and analysis of different oil film thickness under different rotation rates are conducted.

Analysis of Homogeneous Fluid/wall Oil Film Two-phase Stratified Flow in an Aeroengine Bearing Chamber

Analysis of Homogeneous Fluid/wall Oil Film Two-phase Stratified Flow in an Aeroengine Bearing Chamber

A depth-averaged model for non-isothermal thin-film rimming flow

A model for non-isothermal shear-driven thin-film flow on the inside surface of a stationary circular cylinder is presented. Motivated by an application to film flow in an aero-engine bearing chamber the model extends lubrication theory analysis of thin films to retain the important effects of inertia and heat convection.The accuracy of the depth-averaged temperature model is tested and comparisons illustrate the model is accurate for both conduction- and convection-dominant flows although local inaccuracies are introduced in regions exhibiting sharp changes in boundary temperature when convective effects are strong.Three rimming-flow configurations are considered: uni-directional flow with slowly-varying film height, a solution containing a steep front termed a shock, and a pooling solution where fluid accumulates in a recirculation at the base of the cylinder. The temperature field in the latter two which include recirculation features are greatly influenced by the strength of convection in the film.

Inertial effects at moderate Reynolds number in thin-film rimming flows driven by surface shear

In this paper, we study two-dimensional thin-film flow inside a stationary circular cylinder driven by an imposed surface shear stress. Modelling is motivated by a need to understand the cooling and film dynamics provided by oil films in an aero-engine bearing chamber characterised by conditions of very high surface shear and additional film mass flux from oil droplets entering the film through the surface. In typical high-speed operation, film inertial effects can provide a significant leading-order mechanism neglected in existing lubrication theory models. Inertia at leading-order is included within a depth-averaged formulation where wall friction is evaluated similar to hydraulic models. This allows key nonlinear inertial effects to be included while retaining the ability to analyse the problem in a mathematically tractable formulation and compare with other approaches. In constructing this model, a set of simplified mass and momentum equations are integrated through the depth of the film yielding a spatially one-dimensional depth-averaged formulation of the problem. An a priori assumed form of velocity profile is needed to complete the system. In a local Stokes flow analysis, a quadratic profile is the exact solution for the velocity field though it must be modified when inertial effects become important. Extension of the velocity profile to a cubic profile is selected enabling specification of a wall friction model to include the roughness of the cylinder wall. A modelling advantage of including the inertia term, relevant to the applications considered, is that a smooth progression in solution can be obtained between cases of low Reynolds number corresponding to lubrication theory, and high Reynolds number corresponding to uniform rimming-flow. Importantly, we also investigate the effect of inertia on some typical solutions from other studies and present a greater insight to existing and new film solutions which arise from including inertia effects.