Bearing Chamber Research Articles

Analysis of Bubble-Flow Characteristics in Scavenge Pipe and Establishment of a Flow-Prediction Model

In the modern aerospace industry, the importance of a lubrication system is self-evident for aero-engines, and the aero-engine bearing chamber return line is an even more challenging environment, as it involves a complex two-phase flow. The designer of the scavenge pipe needs to have an accurate understanding of the flow conditions in the scavenge pipe. This paper establishes a visual scavenge pipe test system. The flow direction was vertical flow, the test temperature was 370 k, and a high-speed camera was used to take high-definition flow photographs, which can observe the three main flow types: bubble flow, slug flow, and annular flow. Code program was created to analyze many pictures taken to obtain the apparent flow rate and perimeter of bubbles in the pipe under different flow conditions and to explore the gas–liquid two-phase flow in the scavenge pipe. A support vector machine (SVM) was used for data regression prediction, and the converted velocities of the gas–oil phases were inputted as eigenvalues to obtain the predicted values of bubble-flow velocity. The bubble-flow analysis prediction model established in this paper has a good prediction effect with root mean square error RMSE = 0.0172, which can more objectively and accurately describe the bubble-flow characteristics in the scavenge pipe.

ASSESSMENT OF MULTIFLUID, EULERIAN INTEGRAL THIN FILM AND DPM APPROACHES FOR THE NUMERICAL SIMULATION OF A BEARING CHAMBER

In this work several computational approaches are tested for the two-phase simulation of the ELUBSYS bearing chamber in the high-speed regime-a four-equation Eulerian multifluid model, a steady-state Eulerian integral thin film (EITF) approach, a discrete parcel method (DPM) approach, and a simplified EITF-DPM coupled approach. While computationally expensive, the multifluid model captured the global liquid dynamics in the chamber and predicted that most of the oil is in the form of a thin film that flows on the stationary walls. The much more cost-efficient EITF approach achieved accurate results for the oil thickness distribution at the counter-current region but did not account for the large amounts of oil flowing out through the top vent. The DPM approach was used to assess the dispersed phase dynamics in both one-way and two-way coupling configurations, outlining a significant influence of the latter on the gas phase dynamics. Finally, the coupled EITFDPM approach was able to overcome some of the limitations observed by its individual counterparts by predicting a continuous film throughout the chamber circumference and a higher vent outflow, while still retaining most of the expected film distribution characteristics in the bearing chamber.

Parameter optimization design of an aero-engine bearing chamber based on active learning Kriging

The air-oil two-phase flow in the aero-engine bearing chamber is highly complex and unsteady. To obtain the mapping relationship between the oil volume fraction in the chamber and the oil inlet flow rate and rotational speed for further design optimization, the air-oil two-phase flows are simulated using the level set method in COMSOL Multiphysics software. To avoid frequent calls to the simulation model during the optimization process, which consumes huge computational costs, the Kriging model is applied to approximate the true response of the computational fluid dynamics (CFD) simulations. The point addition process is assisted by introducing the active learning function EI to enhance the efficiency of constructing the Kriging model. Particle swarm optimization (PSO) is applied to optimize the Kriging-based optimization objective function. With the optimal parameters’ combination, the performance of the oil return in the aero-engine bearing chamber is improved. This study has guiding significance for the lubrication design of the aero-engine bearing chamber.

Research on Oil–Gas Two-Phase Flow Characteristics and Improvement of Aero-Engine Bearing Chamber

In order to study the oil–gas two-phase flow characteristics of an aero-engine bearing chamber and improve the scavenge effect of lubricating oil, the two-phase flow solution model of a bearing chamber based on the Euler–Euler method was established. Three improvement schemes were proposed for the ventilation structure and scavenge structure of the bearing chamber. The flow characteristics and scavenge characteristics of a conventional bearing chamber and three improvement schemes under different working conditions were analyzed in depth. The results show that after the conventional bearing chamber ventilation structure is embedded (Embed) and improved, with the increase in the embedding depth, the oil in the cavity is further blocked in the cavity, the amount of oil flowing out from the vent is further reduced, and the scavenge efficiency is further improved. After the slope improvement of the scavenge structure of the conventional bearing chamber, due to the increase in the depth of the oil return groove, the drag effect of the air shear force in the cavity on the oil in the oil return groove is further weakened, and the oil accumulation area on the right side of the scavenge port is further suppressed. The volume fraction of the oil in the cavity is further reduced, and the scavenge efficiency is further improved. The combined improvement scheme (ES) can take into account the advantages of embedding and slope improvement schemes, and further improve the scavenge efficiency. Compared to the conventional bearing chamber, when the oil flow rate is 200 L/h and the speed is 15,000 r/min, the oil return efficiency of the embedded (h = 12 mm), slope (l = 56 mm) and combined improvement schemes are increased by 20.19%, 13.43%, and 37.94%, respectively.

Identification of Oil and Gas Two-Phase Flow Patterns in Aero-Engine Bearing Chambers Based on Kriging Method

The identification of the flow pattern within the bearing chamber's oil and gas two-phase flow is crucial for its lubrication design. Aiming at the lack of accuracy and universality of the current bearing chamber oil and gas two-phase flow pattern recognition, this paper introduces a new method for recognising oil and gas two-phase flow patterns based on the Kriging model. In this paper, the oil-gas two-phase flow field in the bearing chamber is modelled in Comsol simulation software using the level set-k- ε model. Subsequently, the finite element analysis results were used as samples to fit the Kriging model, and the effects of different variables on the flow pattern were analysed and compared with the actual results. The results demonstrate that the flow pattern discrimination results fitted by the Kriging model exhibit higher accuracy and greater generalisability. This holds significant implications for future lubrication and structural design of bearing chambers.

THREE-DIMENSIONAL NUMERICAL ANALYSIS OF FLOW AND HEAT TRANSFER CHARACTERISTICS OF OIL/GAS TWO-PHASE MIXTURE IN AERO-ENGINE BEARING CHAMBERS OF DIFFERENT STRUCTURES

The change of the outlet number of bearing chambers can change the pressure distribution in the chamber and the action of the air shear force, which has an important influence on oil/gas two-phase flow and heat transfer. In this paper, the flow and heat transfer characteristics in the ventless bearing chamber and the vented bearing chamber were compared and analyzed by numerical simulation. The accuracy of the numerical model was verified by comparison with the experimental data. Three different rotor speeds were selected, and the lubricating oil distribution, the velocity of oil/gas two-phase flow, and the temperature distribution in the bearing chamber were investigated under different numbers of outlets of the bearing chamber. The heat flux and Nusselt number distribution of convective heat transfer between oil/gas two-phase flow and the outer wall at different rotor speeds were analyzed. The results show that the thickness of oil film increases in the ventless bearing chamber with increase of rotor speed, and when air flow is large, it hinders the uniformity of lubricating oil distribution and the increase of the velocity of oil/gas two-phase flow, but it can improve the uniformity of heat transfer. In the vented bearing chamber, the thickness of oil film decreases with increase of rotor speed, and the speed of oil/gas two-phase flow increases greatly, and the entraining effect of air is obvious. The research results can provide a theoretical reference for improving the number and structure of bearing chambers to improve the performance of lubricating oil system.

Scaling analysis as a tool to validate CFD simulation of a lubricant flow in the bearing housing of a gas turbine

• The effects of rotor speed on the temperature of the lubricant oil are studied. • CFD model of oil flow and heat transfer in the bearing chamber is developed. • Scaling analysis is used to simplify and nondimensionalize the governing equations. • Scaling analysis is used to replace experimental data to validate CFD results. • An equation to compute viscous dissipation energy is obtained by Scaling analysis. This work concentrates on the journal bearing chamber of a gas turbine engine, to explain the impacts of the rotational speed of the rotor on the velocity, pressure and temperature distribution in the bulk oil. In the first step, a CFD model of fluid flow and heat transfer in the bulk oil of the bearing chamber was developed via COMSOL 6. Next, and in a novel approach, scaling analysis was employed to verify the CFD simulation results. Scaling analysis, as a systematic method for non-dimensionalizing a set of equations, was used to simplify the governing equations based on the specific conditions of the physics. Afterward, the velocity, pressure and temperature profiles attained from the CFD simulation were compared to this set of simplified equations. In general, it was confirmed that the CFD model developed in the current article is physically valid and follows the main descriptive equations governing the entire physics of the system. Scaling analysis was effectively used to confirm the simulation results where insufficient experimental results were available, due to the geometrical and operational restrictions in the test rig. Temperature, pressure and velocity were the factors considered in this study and the average of simulation and scaling results for each factor were compared. Additionally, the average point-to-point error between the simulation and scaling results for each factor was reported as another basis for the comparison. In summary, scaling analysis in this work is presented as a straightforward method to substitute experimental measurements in order to validate CFD simulation results.

Математичне моделювання теплопередачі у повітряно-крапельному потоку камери підшипника ГТД

The gas-liquid flow in the bearing chamber (BC) of the gas turbine engine is realized due to the interaction of the sealing air and oil supplied for lubrication and cooling of friction units. The complex nature of the flow movement is determined not only by the BC geometry but also by the presence of rotating elements and the manner of oil supply and flow removal. The most important result for the engineering practice of BC flow modelling is the determination of the heat transfer coefficient to the inner wall. The variety of influencing factors causes difficulties even at the stage of an integral mathematical model of the process formation, which makes it possible to determine this coefficient. As a result, significantly different approaches are used – from three-dimensional CFD modelling of a heterogeneous flow up to the use of a criterion equation that formally considers the effect of geometric and regime parameters on a heat transfer. The first approach requires significant computational resources, and certain difficulties arise in setting the initial and boundary conditions, especially in terms of droplet parameters. Homogeneous models somewhat simplify the problem, including when formulating the boundary conditions. However, all the effects of the influence of the droplet diameter are levelled. In both cases, the computation time is long, and the results of CFD simulations require selective experimental verification. Therefore, it is problematic to use this approach solely for engineering problems, as well as when generalizing experimental data in several regime parameters. When using the criterion equation, the calculation procedures are as simple as possible. However, dimensionless complexes do not ensue from the basic equations of heterogeneous media mechanics and do not consider the effects of interfacial interaction during heat transfer in the BC. Therefore, the possibility of the application of the proposed correlations for other BC geometries and oil and air supplying conditions also needs to be experimentally confirmed. This makes it problematic to use such correlations at the design stage of the BC and the oil system as a whole. The preferred approach for engineering practice is when the thermohydraulic processes in the BC are described on the basis of the proven equations of heterogeneous media mechanics with the transition to a two-dimensional problem by averaging the phase parameters along the axis. This averaging is justified by the fact that the main heat carrier from the core to the inner wall of the BC is the radial flow of droplets. In view of the low volume fraction of droplets, the Lagrange approach is used to simulate a two-phase flow in the BC core. The droplet parameters along the trajectory are calculated considering the interfacial interaction with the air. In this regard, the air velocity field is determined by considering the geometry of the BC, the flow through the seals and the shaft speed. Here, it is possible to consider not only the droplet polydispersity but also the effects of primary droplet reflection, the formation, and movement of secondary droplets during the formation of a near-wall oil film, the thermal resistance of which directly affects the value of the internal heat transfer coefficient.

Simulation of Unsteady Flows of Oil/Gas in the Ventless Bearing Chamber of an Aero-Engine

The unsteady motion behavior of oil/gas two-phase flow in a novel ventless bearing chamber has significant impacts on the lubrication and heat transfer efficiency of bearings due to the various advantages of lower pressure levels and weaker rotating airflow effects. In this paper, the unsteady motion behavior of oil/gas two-phase flow in a ventless aero-engine bearing chamber is investigated by three-dimensional numerical simulation through the volume of fluid (VOF) method, and the numerical method is verified using published experimental data. The flow characteristics of oil/gas two-phase in the secondary flow and three-dimensional flow are investigated. The results show the evolution of vortices and the transition of the driving mode in the unsteady motion of oil/gas two-phase flow, and a criterion for the shift of the driving mode at different rotor speeds is proposed. As the rotation speed increases, the variation trend of the velocity field and pressure field of oil/gas two-phase flow is consistent, and the accumulation region of oil becomes inconspicuous. The results indicate a reference for enhancing the performance of lubrication systems for aero-engines.

Computational modelling of turbulent Taylor–Couette flow for bearing chamber applications: A comparison of unsteady Reynolds-averaged Navier–Stokes models

The capability to accurately model fluid flow within rotating Taylor–Couette systems has a primary role in informing computational investigations of rotating machinery. There is considerable uncertainty regarding selection of modelling approach, including a suitable turbulence model, that can accurately resolve turbulence within such complex flows while remaining computationally feasible for industrially relevant applications. This paper presents a numerical comparison of axisymmetric and three-dimensional unsteady Reynolds-averaged Navier–Stokes (URANS) turbulence models within ANSYS Fluent. The CFD geometries are representative of ones for which there are published experimental measurements. For the Taylor–Couette study, investigation into inner cylinder start-up procedure, based on previous published findings, confirmed that the final state of the flow is highly dependent on the initial conditions and acceleration rate. Once Taylor vortices form and stabilise, they are not disrupted by small steps in inner cylinder speed, allowing computationally efficient accelerations. Investigations into applying rotational periodicity were unsuccessful, resulting in a significantly reduced core velocity. Axisymmetric predictions provided reasonable agreement with experimental data only at low rotation rates. A good prediction of the velocity flow field was obtained for three-dimensional simulations of the full 360° domain with differences of less than 5% for radial velocities. Among the URANS models, the standard k-ω model and baseline Reynolds stress model (BSL-RSM) provided the closest agreement to published experimental data. In the paper, the developed Taylor–Couette turbulence modelling methodology is extended to a bearing chamber geometry. Analysis of the secondary vortex flow field is compared both qualitatively and quantitatively to published bearing chamber experimental measurements. Overall, whilst a good agreement is still found using the standard k-ω turbulence model, discrepancies arise with the BSL-RSM. However, for this more complex bearing chamber environment compared to a Taylor–Couette flow, the shear stress transport k-ω turbulence model provided the closest agreement and is recommended for future bearing chamber modelling.

Specific Aspects in Numerical Simulation of Complex Processes in Gas Turbine Engine Bearing Chamber

The complex interrelation of thermal and hydraulic processes in a gas turbine engine bearing chamber requires modelling methods based on the multiphase flow mechanics and Computational Fluid Dynamics (CFD) to predict the fluid distribution and heat transfer phenomena. This paper presents a study of different approaches to CFD modelling of multiphase oil-air flow in the bearing chamber. The Volume of Fluid and Eulerian multiphase models, Steady and Transient solvers, “Realizable k-ε” and “k-ω SST” turbulence models were analysed. The Eulerian Wall Film Model implemented in ANSYS Fluent was applied to model an oil film formation on the bearing chamber walls. The CFD results were compared with available experimental data to formulate practical recommendations for precise modelling of processes in the bearing chamber.

Inhibiting Coking of Lubricating Oil and Thermal Insulation of Bearing Chamber Wall by TCA-2 Nitride Ceramic Coating.

High temperature around the rear bearing chamber of supersonic aero-engines often causes the coking of the lubricating oil on the shaft end cover. To figure out the problem, a method using the TCA-2 nitride ceramic coating with the thickness of several micrometers is proposed. A simulation experiment method of lubricating oil coking for high-temperature parts is developed, and the anticoking performance of the samples with the coating is studied. The results showed that the TCA-2 coating inhibits the coke of lubricating oil on the metal surface within a certain temperature range by about 40.7% under the 500 °C attributed to the decrease in the surface activity of high-temperature metal and increase in the heat resistance. The TCA-2 coating also shows good compatibility with the lubricating oil since the acid value change of lubricating oil decreases after the thermal oxidation experiment. The TCA-2 coating can effectively reduce the surface temperature of the oil side.

Simulation of a Simplified Aeroengine Bearing Chamber Using a Fully Coupled Two-Way Eulerian Thin Film/Discrete Phase Approach Part II: Droplet Behavior in the Chamber

Abstract Within aeroengines, bearing chambers exhibit a highly complex two-phase environment as a result of the complex air/oil interactions. The desire to operate at both higher temperatures and shaft speeds requires a sufficient understanding of these systems for design optimization. Typically, bearings are used to support the radial and axial loads transmitted by the shafts and require oil for lubrication and cooling. These bearings are housed in bearing chambers that are sealed using airblown seals. Efficient scavenging systems ensure that the oil is collected and returned to the tank avoiding any unnecessary working of the oil. Previous work at the Gas Turbine and Transmissions Research Center (G2TRC) has highlighted the need for an adequate computational model which can appropriately model the oil shedding behavior from such bearings. Oil can breakup forming droplets and ligaments, subsequently forming thin and thick films driven by both gravity and shear. The objective of this paper is to explore the modeling capability of fully two-way coupled Eulerian thin film/discrete phase models (ETFM-DPM) applied to our simplified bearing chamber configuration. The models are created using openfoam and two-way coupling is employed, enabling Lagrangian droplets to either impinge on the film surface or be removed through effects such as film stripping, splashing, or edge separation. This paper focuses on the droplets, presenting statistics relating to size, velocity, impingement, and residence time, and provides insight into solution sensitivity to operational parameters including shaft speed and oil flow rate. This extends upon our previously published work and improves bearing chamber modeling capability.

Simulation of a Simplified Aeroengine Bearing Chamber Using a Fully Coupled Two-Way Eulerian Thin Film/Discrete Phase Approach Part I: Film Behavior Near the Bearing

Abstract Previous work at the Gas Turbine and Transmissions Research Center (G2TRC) has highlighted the need for an adequate computational model, which can appropriately model the oil shedding behavior from bearings. Oil can break up forming droplets and ligaments, subsequently forming thin and thick films driven by both gravity and shear. Our previously published work using openfoam successfully coupled the Eulerian thin film model (ETFM) with the discrete phase model (DPM) (Nicoli et al., 2019, “A New OpenFOAM Solver Capable of Modelling Oil Jet-Breakup and Subsequent Film Formation for Bearing Chamber Applications,” ASME Paper No. GT2019-90264.). In this paper, the previously developed ETFM-DPM capability is, for the first time, extended to an aeroengine representative bearing chamber configuration. The configuration matches that of a simplified aeroengine bearing chamber that has been investigated by researchers at the Gas Turbine and Transmissions Research Center (G2TRC). Numerical investigations are conducted for three different shaft speeds, namely, 5000, 7000, and 12,000 rpm, at two different oil flow rates: 7.3 liters/minute and 5.2 liters/minute. CFD results are validated against existing experimental data for the two lower shaft speeds. Evaluation of computed mean film thickness shows excellent agreement with the experimental data. Results show that there is a diminishing reduction of film thickness with an increasing shaft speed. The computational study allows investigation of oil residence time in the annulus near the bearing. Residence time is seen to reduce with increasing shaft speed and with increasing oil flow rate. This CFD investigation represents the first successful fully coupled two-way ETFM-DPM investigation into the droplet generation process within a bearing chamber application, establishing a firm foundation for future aeroengine bearing chamber modeling.

Modeling of Partially Wetting Liquid Film Using an Enhanced Thin Film Model for Aero-Engine Bearing Chamber Applications

Abstract In the case of aero-engine, thin lubricating film servers dual purpose of lubrication and cooling. Prediction of dry patches or lubricant starved region in bearing or bearing chambers are required for safe operation of these components. In this work, thin liquid film flow is numerically investigated using the framework of the Eulerian thin film model (ETFM) for conditions, which exhibit partial wetting phenomenon. This model includes a parameter that requires adjustment to account for the dynamic contact angle. Two different experimental data sets have been used for comparisons against simulations, which cover a wide range of operating conditions including varying the flowrate, inclination angle, contact angle, and liquid–gas surface tension coefficient. A new expression for the model parameter has been proposed and calibrated based on the simulated cases. This is employed to predict film thickness on a bearing chamber which is subjected to a complex multiphase flow. From this study, it is observed that the proposed approach shows good quantitative comparisons of the film thickness of flow down an inclined plate and for the representative bearing chamber. A comparison of model predictions with and without wetting and drying capabilities is also presented on the bearing chamber for shaft speed in the range of 2500 RPM to 10,000 RPM and flowrate in the range of 0.5 liter per minute (LPM) to 2.5 LPM.

Scavenge Performance of an Optimized Shallow Sump at Various Flow Conditions

Abstract Oil scavenge flow in aero-engine bearing chamber remains largely a challenging problem for many engine designers. Research campaign on scavenge flow has been conducted by G2TRC—Gas Turbine and Transmissions Research Centre (previously Rolls Royce University Technology Centre in Gas Turbine Transmission Systems) at the University of Nottingham. It was recognized that a deep sump performs better than shallower one due to its ability to “shield” the collected oil in the sump from the shaft windage, thus reducing the amount of oil being picked up by the bulk air rotation. However, such a deep sump design cannot be employed in some engines and especially at certain locations where space is limited. A parametric study combined with phenomenological approach on shallow sump geometry has been conducted and presented in the previous publication, where a certain optimized shallow sump variant was proposed depending on whether the flow in the chamber is wall film dominated or airborne droplets dominated. The parametric phenomenological approach was employed since it can be done relatively quicker than typical data gathering through an experiment. However, the approach relies on qualitative interpretation of the flow features, and its application in bearing chamber flow research has never been validated before. This paper presents the results of quantitative measurements of residence volumes of an optimized shallow sump variant identified in the parametric phenomenological study. Comparison was then made with the residence volumes of some existing engine sumps. It was found that the optimized shallow sump for wall film dominated flow has lower residence volumes compared to some existing engine sumps. In some cases, the residence volume can be reduced by up to 75%. An optimized shallow sump variant for airborne droplets dominated was also identified in the previous parametric phenomenological study, although the residence volume measurement is yet to be conducted. The optimized shallow sump for wall film dominated flow was also identified as a good sump regardless of the flow regime. However, when it was tested in airborne droplets dominated flow, its residence volumes are higher than some of the existing engine sumps. This highlights the importance of considering the flow regime in the bearing chamber in any attempt to optimize a sump geometry.

Numerical Simulation of the Oil Droplet Size Distribution Considering Coalescence and Breakup in Aero-Engine Bearing Chamber

In order to improve the inadequacy of the current research on oil droplet size distribution in aero-engine bearing chamber, the influence of oil droplet size distribution with the oil droplets coalescence and breakup is analyzed by using the computational fluid dynamics-population balance model (CFD-PBM). The Euler–Euler equation and population balance equation are solved in Fluent software. The distribution of the gas phase velocity field and the volume fraction of different oil droplet diameter at different time are obtained in the bearing chamber. Then, the influence of different initial oil droplet diameter, air, and oil mass flow on oil droplet size distribution is discussed. The result of numerical analysis is compared with the experiment in the literature to verify the feasibility and validity. The main results provide the following conclusions. At the initial stage, the coalescence of oil droplets plays a dominant role. Then, the breakup of larger diameter oil droplet appears. Finally, the oil droplet size distribution tends to be stable. The coalescence and breakup of oil droplet increases with the initial diameter of oil droplet and the air mass flow increasing, and the oil droplet size distribution changes significantly. With the oil mass flow increasing, the coalescence and breakup of oil droplet has little change and the variation of oil droplet size distribution is not obvious.

Analysis of Oil Droplet Deposition Characteristics and Determination of Impact State Criterion in Aero-Engine Bearing Chamber

The research of oil/air two-phase flow and heat transfer is the fundamental work of the design of lubrication and heat transfer in aero-engine bearing chamber. The determination of impact state criterion of the moving oil droplets with the wall and the analysis of oil droplet deposition characteristics are important components. In this paper, the numerical analysis model of the impact between the moving oil droplet and the wall is established by using the finite volume method, and the simulation of oil droplet impingement on the wall is carried out. Then the effects of oil droplet diameter, impact velocity, and incident angle on the characteristic parameters of impact state are discussed. The characteristic parameters include the maximum spreading length, the maximum spreading width, and the number of splashing oil droplets. Lastly the calculation results are verified through comparing with the experimental results in the literature. The results show as follows: (1) The maximum spreading width of oil droplet firstly increases and then slows down with the incident angle and the oil droplet diameter increasing; (2) when the oil droplet diameter becomes small, the influence of the incident angle on the maximum spreading length of oil droplet is obvious and vice versa; (3) with the impact velocity and diameter of oil droplet increasing, the maximum spreading width of oil droplet increases firstly and then slows down, and the maximum spreading length increased gradually; (4) the number of splashing oil droplets increases with the incident angle and impact velocity increasing; and (5) compared with the experimental data in literature, the critical dimensionless splashing coefficient K c proposed in this paper can better distinguish the impact state of oil droplet.

Study of sealing mechanism of gas-liquid miscible backflow pumping seal

Abstract This work presents a gas-liquid miscible backflow pumping seal (G-LMBPHS) aimed to seal lubricating oil in a high-speed bearing chamber as presented in this paper. The sealing mechanism and performance of the G-LMBPHS are numerically investigated and validated experimentally with a visualization test device, and the theoretical results fundamentally accord with the experimental values. The results reveal that G-LMBPHS uses high pressure fluid generated by the hydrodynamic effect of the groove to prevent the leakage of lubricating oil. When the shearing action generated by the rotational speed completely cancels out or even exceeds the pressure, G-LMBPHS can achieve perfect sealing with no any leakage of the lubricating oil. And G-LMBPHS designed in this study will have wide applications in engineering.

Influences of the Geometry of the Scavenge Pipe on the Air-Oil Two-Phase Flow and Heat Transfer in an Aero-Engine Bearing Chamber.

In order to improve the characteristics of the air–oil two-phase flow and heat transfer in the scavenge pipe of an aero-engine bearing chamber, this paper presents several scavenge pipes with different cross-sectional geometries, by numerically investigating the processes of the air–oil two-phase flow and heat transfer, in comparison to a circular pipe. The findings indicate that the tripetal cross-section shows the best heat-transfer effect, while the four-petal cross-section has the lowest flow resistance. Under the same working condition and the equal wetted perimeter, the tripetal cross-section has an 8.8% higher heat-transfer effect than the circular section, while the four-petal cross-section has a 28.6% lower flow resistance than the circular; under the equal cross-sectional area, the tripetal cross-section has a 9.1% higher heat-transfer effect than the circular section, while the four-petal cross-section has a 23.6% lower flow resistance than the circular; under the equal hydraulic diameter, the tripetal cross-section has a 9.2% higher heat-transfer effect than the circular section, while the four-petal cross-section has a 21.9% lower flow resistance than the circular. Taking both the heat transfer and flow resistance into consideration, the four-petal cross-section exhibits the best comprehensive performance, with the comprehensive performance coefficient decreasing with the increase of oil inlet velocity and rising with the increase of air inlet velocity.