Oil Jet Lubrication Research Articles

Transient Simulation Analysis of Needle Roller Bearing in Oil Jet Lubrication and Planetary Gearbox Lubrication Conditions Based on Computational Fluid Dynamics

The transient lubrication conditions of rolling bearings are different in gearboxes and bearing testers. It has been observed that samples of qualified rolling bearings tested in rolling bearing testers often fail and do not meet lifespan requirements when employed in other lubrication conditions. This may be caused by different factors affecting the bearing in testing and applying lubrication. Needle roller bearings were selected for this study to investigate the causes of this phenomenon in terms of lubrication. Based on the computational fluid dynamics (CFD) method, fluid domain models for the same type of rolling bearings with different lubrication conditions were established. The transient flow fields of rolling bearings with oil jet lubrication in a tester and splash lubrication in a planetary gearbox were simulated. The air–oil transient distribution of rolling bearings in two kinds of lubrication was analyzed. The results indicate that the rotational speed significantly affected the oil jet lubrication of the needle roller bearing. The average oil volume fraction rose by 0.2 with the increase in the bearing speed from 1200 r/min to 6000 r/min and by 0.06 with the increase in the oil jet velocity from 8 m/s to 16 m/s. The splash lubrication of the bearings in the planetary gearbox was directly related to the immersion depth of the rolling bearings in the initial position. Meanwhile, the splash lubrication of the bearings was also affected by other factors, including the initial layout of the planetary gears. The increase in speed from 1200 r/min to 6000 r/min made the average oil volume fraction of splash lubrication decrease by 4.4%. The average oil volume fraction of the bearings with splash lubrication was better than that with oil jet lubrication by an average of 41.9% when the bearing speed was in the low-speed stage, ranging from 1200 r/min to 3600 r/min. On the contrary, the bearings with oil jet lubrication were better than those with splash lubrication by an average of 31.8% when the bearing speed was in the high-speed stage, ranging from 4800 r/min to 6000 r/min.

Research on mechanism of enhancing lubrication flow field regulation of high-speed bearing functional cage

With the development of major equipment towards high power density, the bearing speed is getting higher and higher. In the oil-jet lubrication mode, the fluid in the bearing chamber is a two-phase flow of oil and air. Under high-speed operating conditions, the air in the bearing chamber has a significant impact on the lubricating oil flow field and bearing temperature. This article presents a functional cage with wing structures that is designed to regulate the fluid flow field inside the bearing chamber. The numerical simulation model of 2/14 bearing is established. Through computational fluid dynamics (CFD) software, the effects of wing angle, position and length on the regulation of the flow field in the bearing cavity and the axial velocity are analyzed. The results indicate that appropriately increasing the angle and length of the wings, while positioning them closer to the inlet, is an effective way to enhance the regulation of the bearing flow field. The calculation of oil-air two-phase flow and temperature rise test verify that the functional cage bearing has the function of enhancing lubrication and heat dissipation. This research offers both a theoretical basis and practical approaches for developing high-speed bearings that have better lubrication performance and improved heat dissipation.

Experimental Study and Numerical Analysis on Windage Power Loss Characteristics of Aviation Spiral Bevel Gear with Oil Injection Lubrication

With the increasing speed of aviation spiral bevel gears, the load-independent windage power losses caused by hydrodynamic have increasingly more influence on gear transmission efficiency. Firstly, a test rig for the windage power loss of spiral bevel gear under oil-jet lubrication is established, and on this basis, a method for measuring windage torque is proposed. Next, the interactive effects of different injection lubrication parameters on the windage power loss were studied by orthogonal experiment, and the formula for calculating the windage loss was obtained by fitting the experimental data. Then, the fluid distribution, velocity field and pressure field around the gear were analysed by using a computational fluid dynamics (CFD) numerical model, and the mechanical and energy characteristics of the gear windage power loss were obtained. Finally, the dimensionless processing of the windage moment was carried out, and the variation of the dimensionless windage moment coefficient with the rotational Reynolds number is obtained. The comparison between the dimensionless windage moment coefficient of experimental data and simulation results shows that the CFD values are in good agreement with the measured data. This study provides experimental and methodological guidance for the calculation of windage power loss and windage reduction design of aviation gear pair under oil injection lubrication.

Generalized analytical model for evaluating the gear power losses transition changing from windage to churning behavior

Although splash lubrication is usually adopted in the intermediate or tail gearbox of helicopters at low or moderate speed, and it appears that the oil jet lubrication used in a high-speed main reducer of helicopters would be turned into the splash lubrication that only a small part of gears is immersed in the oil sump due to the lubricating oil deposition by the mismatch between the oil feed and return. The classic drag power losses model is either used for the churning behavior of common splash lubrication or the windage behavior of oil jet lubrication, and is no longer suitable for this transition phenomenon of these two behaviors coexist. In this paper, a theoretical analytical method by introducing the windage contribution factor and air-oil ratio evolution model is proposed to predict the associated power losses for one single spur gear rotating partially immersed in an oil bath. To verify the accuracy and correctness, the theoretical calculations are then compared with the existing experimental data from Quiban et al. [33]. Based on this method, a generalized analytical model to evaluate the gear drag power losses for the windage, churning phenomenon and their transition behavior are established.

Influence of Nozzle Layouts on the Heat-Flow Coupled Characteristics for Oil-Jet Lubricated Spur Gears

Aiming to explore the influence of nozzle layouts on the lubrication and cooling performance of spur gears under oil jet lubrication conditions, this paper introduces a heat-flow coupled analysis method to predict the temperature field of the tooth surface with different nozzle layouts. Firstly, the friction heat formulas integrating the coefficient of friction and average contact stress are presented for calculating heat generation. We also present the impingement depth model, which considers the nozzle orientation parameters, jet velocity, and gear structure of the given spur gear pair for laying out the nozzle. Then, a heat-flow coupled finite element analysis method is exploited to resemble the jet lubrication process and gain the gear temperature characteristics. Finally, the numerical results of this model compare well with those of the experiments, showing that this heat-flow coupled model provides accurate temperature prediction, indicating that the nozzle layouts determined as a function of the oil jet height, deviation distance, and oil injection angle significantly influence the lubrication and cooling performance. Further, this study also reveals that the lubrication performance in cases where the nozzle approaches the side of the pinion is relatively superior.

Performance of a New Aeronautic Oil-Guiding Splash Lubrication System

Among ever-increasing demands for low power consumption, low weight, and compact reducer systems, an oil-guiding splash lubrication method integrating the oil-guiding cylinder and pipes is suggested to be more suitable for light helicopters, instead of conventional splash or oil jet lubrication. Aiming at improving the lubrication and cooling performance of this special lubrication method, this paper introduces an oil-guiding channel to increase oil quantity reaching the driving gear, bearings, and spline. Firstly, the lubrication and cooling effect of the oil-guiding channel in the main gearbox is investigated at various speeds and oil depths by leveraging with a computational fluid dynamics (CFD) technique. Then, a specialized test bench is set up and utilized for experiments to verify the CFD study. These results show that the numerical results are very satisfactory with the data of experimentation, and the maximum value of relative errors is no more than 15%. What is more, the oil flow rate passing through the monitoring plane with the oil-guiding channel is much greater than that without the channel by about three orders of magnitude. It also suggests that the oil-guiding channel could dramatically increase the lubricating oil in the meshing gear pair, and significantly improve the lubrication and cooling effect.

Numerical Calculation Analysis and Characteristic Research on Windage Loss of Oil-Jet Lubricated Aviation Gear Pair

The VOF (volume of fluid) multiphase transient simulation model of the windage loss of the gear pair under oil-jet lubrication was carried out by using the dynamic mesh technology with the powerful parallel computing capabilities of the Super Cloud Computing Center. Firstly, a two-phase (oil-gas) turbulence numerical model was established in the process of oil-jet lubrication. The numerical simulation test was designed by orthogonal experiment. The influence of the oil-jet lubrication parameters and their interaction on the windage power loss was studied by means of variance analysis. The results showed that the influence of injection speed on the windage power loss was the largest and proportional, followed by injection temperature and injection pressure, and the latter two factors were inversely proportional. Then, the fitting calculation formula of windage loss related to each influencing factor is obtained based on the numerical simulation results. Furthermore, by observing the velocity vector distribution of the internal flow field of the gearbox with different time, the formation mechanism of windage loss is understood intuitively, and the measures to reduce windage loss are put forward. Finally, the mechanical and energy characteristics of the windage loss under different oil injection parameters are proposed, by analyzing and calculating the differential pressure force, viscous force, turbulent kinetic energy, and turbulent dissipation rate around the gear pair. This paper provides a method guidance for the calculation of windage power loss and efficiency of aviation gear pair under elastohydrodynamic lubrication in engineering application.

Numerical Analysis for Wetting Behaviors of an Oil Jet Lubricated Spur Gear

As it is widely employed in the aeronautical transmission system, a better understanding of the oil jet lubrication behavior is vital to determine the total system energy consumption. Firstly, this study presents related theoretical models such as the sum of oil jet resistance torque, impingement depth, and wetted area of the oil film for calibrating the physical characteristics of the impact of the oil jet on the gear flank. Then, in terms of the flow phenomenology of the liquid column for the oil jet impact on an isolated spur gear, a detailed transient and spatial flow field analysis becomes available, benefiting from an overset mesh method integrating with a volume-of-fluid (VOF) method. Furthermore, not only the oil jet resistance torque, but also the impingement depth as well as the spatial and temporal evolution of wetted surface by the oil film on the gear tooth given by numerical investigations were compared well with the theoretical calculations.

Numerical and Experimental Investigation of Oil-Guiding Splash Lubrication in Light Helicopter’s Reducers

Limited by the space and weight of the reducer, it is difficult to use traditional oil-jet lubrication and splash lubrication for a light helicopter, so an oil-guiding splash lubrication method is adopted as a research object in this paper. Firstly, the lubrication performance of the oil-guiding cylinder in the main reducer under different rotating speeds, oil levels, and flight attitudes is investigated based on the computational fluid dynamics (CFD) method. Then, a specific test rig is developed, and lubrication tests are carried out to verify the feasibility and correctness of the simulation. These results show that oil level, rotating speed, and flight attitude have a great influence on splash lubrication performance.

LUMEN Turbopump: Preliminary Thermal Model

The DLR LUMEN (Liquid Upper stage deMonstrator ENgine) rocket engine comprises of two separate turbopumps, one each for Liquid Oxygen (LOX) and Liquified Natural Gas (LNG) supply. In both turbopumps, an identical bearing block separates the pump section from the turbine section. In the current design, the bearing block features an oil-jet lubrication system to cool and lubricate the bearings during operation. Cryogenic conditions at the pump-interface and high temperature conditions at turbine-interface impose thermal constraints on the selection of a suitable lubricant for the bearing assembly and the design of the lubrication system.As a starting point to address this challenge, this paper presents a preliminary uncoupled finite element thermal model of the LUMEN LOX turbopump. The thermal model investigates the thermal behavior of the housing and rotor components in the bearing housing from start-up to shutdown of the turbopump. The model employs thermal worst case conditions to establish the operational thermal envelope of the turbopump system. Spatial and temporal evolution of the temperature at critical points within the bearing housing are reported.The model, albeit the uncertainties rooted from its empirical nature, provides beneficial insight into the thermal characteristics of the turbopump assembly. This serves as a first estimate of the thermal constraints for the selection of lubricant oil.

Numerical analysis on heat-flow-coupled temperature field for orthogonal face gears with oil–jet lubrication

Lubrication and cooling performances of face gears with oil–jet lubrication are closely related to the nozzle layouts. To investigate the influence of the nozzle layouts on the lubrication performance of the face gears, a numerical analysis method based on heat-flow coupling is adopted in this study for predicting the transient temperature characteristics. First, a mathematical model of impingement depth integrating the nozzle spatial layouts, injection parameters, and geometric parameters of the given face gear is presented for determining the nozzle. Then, after accessing the friction heat, the heat-flow-coupled finite element model is built to resemble the oil–jet lubrication process and obtain the temperature field on the tooth surface. Finally, under the same nozzle layouts, the temperature distributions are compared with the oil pressure and oil volume fraction reported in previous studies. The results reveal that the nozzle layouts significantly affect lubrication performance. Specifically, the lubrication performance of the lateral layout parameter near the middle point of the tooth width is better, and there is a certain range for the longitudinal layout parameter and jet elevation angle. This study can provide a reference for further optimizing the nozzle layouts and prolonging the service life of the orthogonal face gear.

Experimental Investigations About the Power Loss Transition Between Churning and Windage for Spur Gears

Abstract Oil sump lubrication is commonly used in gearboxes. When considering consistent speeds, oil immersion is usually set to low level in order to reduce associated power losses. This configuration is already used in some parts of helicopter mechanical transmissions, and it is under consideration as a lubrication solution for future electric powertrain where gearbox input speeds may be very high. The gear drag power losses are generally evaluated from either a churning power loss model for classic oil sump lubrication or a windage power loss model for oil jet lubrication. One may thus wonder how to estimate drag losses when considering a gear that only a small part is immersed. In this study, the authors investigate the transition between churning and windage phenomena for a spur gear. A series of torque measurements on a single spur gear rotating in an oil bath at numerous oil immersion levels have been carried out. Based on these results, a criterion to indicate which power loss model to use is proposed.

Mathematical modeling and numerical simulation for determining an optimized oil jet layout for spiral bevel gear lubrication

In aeroengine industry, the oil jet layout significantly influences lubrication of high-speed and heavy-load transmission gears, as there is only extremely limited meshing clearance for the oil stream jetting into and an inevitable blocking effect of rotating gears. A novel mathematical model for calculating the exact impingement depth of the lubrication oil jet on the spiral bevel gear surface has been established, and it contains comprehensive and detailed design parameters for the jet nozzle layout and meshing gears. Furthermore, under different jet layout parameters conditions, computational fluid dynamic numerical simulations for oil jet lubrication of an aeronautical spiral bevel gear pair were conducted and, then, the simulation results are compared with the impingement depths based on the mathematical model. The simulation results reveal that the oil volume fraction and oil pressure on the meshing area increase with the impingement depth, validating the effectiveness and reliability of the method using the impingement depth mathematical model for evaluating oil jet lubrication. Optimized oil jet layout parameters including the jet nozzle position, jet elevation angle, and jet azimuth angle have been determined and recommended, and they provide valuable theoretical design methods and technical guidance for oil jet lubrication optimization for various practical high-speed and heavy-load spiral bevel gears.

Experimental and numerical investigations on rolling element bearing thermal behaviour

In the present study, some measurements have been conducted on a dedicated test rig to investigate rolling element bearing thermal behaviour. This test rig makes possible the determination of the tested rolling element bearing power losses through the resistive torque measurement. Some thermocouples are located on fixed parts of the system (housing, rolling element bearing outer ring) and others on rotating parts (rolling element bearing inner ring and shaft) via a telemetry system. A deep groove ball bearing, whose pitch diameter is equal to 85 mm, has been tested under oil jet lubrication for different operating conditions. Measurements of the penetration ratio, defined as the proportion of oil actually entering the rolling element bearing versus the oil injected, have also been conducted. An extended thermal network of the test rig has been established to enable a closer understanding of the rolling element bearing inner thermal behaviour. Based upon the first principle of thermodynamics for transient conditions, the studied system is divided into lumped elements at uniform temperature connected by thermal resistances which account for conduction, radiation and convection. Convection within the rolling element bearing depends on the amount of oil in the oil–air mixture known as the volume fraction. At specific test conditions, the developed model found good agreements with experiences for a given oil volume fraction of 15%. This value of volume fraction leads to an adapted formula for volume fraction in the case of jet lubrication which includes the measured penetration ratio.

Determination of an Optimal Oil Jet Nozzle Layout for Helical Gear Lubrication: Mathematical Modeling, Numerical Simulation, and Experimental Validation

To provide a basic guidance for the selection of nozzle layout, a mathematical model of the impingement depth for helical gears under oil jet lubrication is established. Furthermore, computational fluid dynamics (CFD) methods are adopted to validate the effectiveness and accuracy of the derived impingement model. Firstly, the distribution characteristics of the oil volume fraction and oil-gas pressure in meshing area were obtained in flow field simulation. Meanwhile, the influence of spray angle, jet velocity, and gear ratio on lubrication effect was obtained. Then, the transient temperature field of the tooth surface was simulated by the method of thermal-fluid coupling analysis, and the lowest temperature distribution and the corresponding oil jet velocity were determined. Finally, experiments on the temperature characteristics measured by an infrared thermal imager of helical gears with different nozzle parameters were carried out in a gear test rig. The simulation results of transient temperature field are in good agreement with those obtained by experiments, and it indicates that the thermal-fluid coupling analysis method is correct and feasible to predict the temperature field of the helical gear pair under oil injection jet lubrication.

CFD modelling and numerical simulation on windage power loss of aeronautic high-speed spiral bevel gears

With the widespread of spiral bevel gears in aero-engines applications, it becomes a burning challenge to reduce the windage power loss owing to the high-speed rotation of these gears. As shrouding the gears has been manifested as an effective approach to reducing windage power losses and restricting the flow in the vicinity of gear teeth, a shroud in this paper is introduced to enclose the high-speed unmeshed spiral bevel gear. By leveraging the CFD software and selecting multi reference frame (MRF), the windage behavior of our proposed model is evaluated and compared with that without a shroud, and the influence of rotational speed of the bevel gear on windage power loss is also analyzed. Furthermore, further attention has been paid to the effects of the spacing between the bevel gear and the shroud. including the toe clearance, the face clearance and the heel clearance. Simulation results demonstrate that the windage power loss dramatically increases with the increment of the gear speed, and the windage power loss of the enclosing bevel gear declines rapidly by 80 percent relative to the bevel gear without a shroud. Moreover, it observes that the trend of windage power loss reducing with the decreasing spacing between the shroud and the bevel gear, finding the optimal spacing. This paper provides prerequisites towards pursuing the researches on the windage loss of meshing spiral bevel gears under oil-jet lubrication.

An Experimental Investigation on the Wear of Lubricated Steel Against PEEK Gears

Abstract The application of polymer gears in power transmission has been considered recently due to their advantages over metal gears, e.g., lighter weights and lower costs. Much further research work needs to be carried out to understand their wear mechanisms and to establish their design methods. This paper aims to investigate the wear and failure behavior of the poly-ether-ether-ketone (PEEK) gear against the steel gear under oil jet lubrication through the durability test with the standard FZG test rig. The service life and wear loss of PEEK gears were experimentally recorded under different moderate loading conditions ranging from the output torque of 10–20 Nm with a fixed input rotational speed of 1000 rpm. Moreover, the tooth surface morphologies and the wear loss of PEEK gears under different running stages were investigated. The experimental measurements reveal that there is a critical load magnitude for the transition of wear performance. With a load above 15 Nm, the PEEK gear wear rate increases rapidly, leading to a quick breakage failure, whereas the gear wear rate with a torque below 15 Nm is much lower. All tested PEEK gears finally failed with a pitting-induced tooth breakage mode under moderate loading conditions.

Evaluation and Optimization of the Oil Jet Lubrication Performance for Orthogonal Face Gear Drive: Modelling, Simulation and Experimental Validation

The oil jet lubrication performance of a high-speed and heavy-load gear drive is significantly influenced and determined by the oil jet nozzle layout, as there is extremely limited meshing clearance for the impinging oil stream and an inevitable blocking effect by the rotating gears. A novel mathematical model for calculating the impingement depth of lubrication oil jetting on an orthogonal face gear surface has been developed based on meshing face gear theory and the oil jet lubrication process, and this model contains comprehensive design parameters for the jet nozzle layout and face gear pair. Computational fluid dynamic (CFD) numerical simulations for the oil jet lubrication of an orthogonal face gear pair under different nozzle layout parameters show that a greater mathematically calculated jet impingement depth results in a greater oil volume fraction and oil pressure distribution. The influences of the jet nozzle layout parameters on the lubrication performance have been analyzed and optimized. The relationship between the measured tooth surface temperature from the experiments and the corresponding calculated impingement depth shows that a lower temperature appears in a situation with a greater impingement depth. Good agreement between the mathematical model with the numerical simulation and the experiment validates the effectiveness and accuracy of the method for evaluating the face gear oil jet lubrication performance when using the impingement depth mathematical model.

Comparison of heat generation estimation methods for angular contact ball bearings

The article reviews domestic and foreign methods of estimating heat generation in angular contact ball bearings. Models for general-purpose bearings and for aviation angular contact ball bearings are considered. Models adopted at bearing manufacturers FAG (Germany) and SKF (Sweden) are considered for general-purpose bearings. Models developed at the KAI, CIAM named after P.I.Baranov and MTU (Germany) are considered for aviation bearings. The results of heat generation obtained in testing bearings 126206 (306216 mm) and 176126 (13020033 mm) are presented. The calculated heat generation values, obtained by various methods, are compared with the experimental data. On the basis of the research the models that yield the calculated values of heat generation in ball bearings closest to the experimental data are specified. They can be used to estimate heat generation in aviation roller bearings with oil jet lubrication.

Numerical Simulation and Optimization of Oil Jet Lubrication for Rotorcraft Meshing Gears

Numerical Simulation and Optimization of Oil Jet Lubrication for Rotorcraft Meshing Gears