1. Introduction
Aviation high – speed gear pumps are crucial power output devices in aircraft hydraulic systems. To meet the development requirements of high thrust – to – weight ratio and low fuel consumption of aircraft, gear pumps need to increase the flow rate without increasing the volume and mass, which requires a higher rotational speed design. However, high speed exacerbates the wear of the gear end face friction pairs in gear pumps, reducing the service life and volumetric efficiency, and seriously affecting the stable and reliable operation of the aircraft hydraulic control system.
1.1 Research Background
The wear of gear end face friction pairs has been a significant problem in the field of gear pumps. Many scholars have conducted research on the tribological characteristics of gear pump friction pairs to understand the wear mechanism and control methods. For example, Szwemin et al. established a three – dimensional gear pump model to obtain the variation law of the gear end face liquid film pressure with time. Guo et al. combined theory and experiments to study gear pumps and found that an increase in the outlet pressure causes fluctuations in the internal flow field of the gear pump, thereby exacerbating gear end face wear.
1.2 Significance of Surface Textures
Surface textures have been proven to effectively improve the lubrication performance between friction pairs. Since the 1960s, researchers have used laser processing technology to create micro – and nano – textures on the surfaces of sealing elements and found that these textures can form a certain hydrodynamic pressure effect and reduce wear. In recent years, various types of textures, such as grooves and holes, have been studied, and their applications in different mechanical components have shown promising results in improving lubrication and reducing friction.
2. Gear Pump End Face Friction Pair Structure and Geometric Model
2.1 Structure of the Gear Pump End Face Friction Pair
The gear pump end face friction pair consists of a gear and a floating side plate. In this study, a new compound texture combining Tesla valve groove type and elliptical shape is opened on the gear end face. When the gear rotates at high speed, a lubricating liquid film with a thickness of several microns is formed between the gear end face friction pairs under the action of the hydrodynamic pressure effect of the lubricating texture.
2.2 Geometric Model
The geometric model of the compound texture end face includes two parts. The first part is the 仿 Tesla valve type groove composed of a spiral groove and a return groove. The spiral groove has a classic logarithmic spiral line, and the return groove is composed of multiple tangent circular arcs. The second part is the elliptical hole texture opened on the gear tooth end face. The specific parameters of the geometric model are defined, such as the radius of the spiral groove, the depth of the grooves and holes, and the dimensions of the elliptical holes.
3. Theoretical Analysis Model
3.1 Basic Assumptions of the End Face Liquid Film Flow Field
To establish an accurate theoretical analysis model, several assumptions are made based on the basic theory of fluid mechanics and the characteristics of the fluid medium on the textured end face. These assumptions include regarding the fluid in the end face as a continuous medium with constant temperature and viscosity, ignoring the influence of body forces, fluid film slip, friction heat, and end face deformation and system vibration on the flow field.
3.2 Flow State Judgment Equation
The flow state of the end face liquid film is determined by calculating the flow factor ζ. By comparing ζ with specific values, the flow state can be classified as laminar, turbulent, or in a transition zone. In this study, based on the given numerical simulation conditions, the flow state is determined to be laminar, and a laminar model is adopted for subsequent simulations.
3.3 Control Equations
Since the end face liquid film may experience cavitation due to negative pressure, a Mixture multiphase flow model is selected for the simulation model. The continuity and momentum control equations of the multiphase flow, as well as the cavitation model (Schnerr – Sauer model), are introduced. These equations describe the behavior of the fluid mixture and the cavitation effect accurately, allowing for the calculation of important lubrication characteristic parameters such as the opening force and leakage rate.
3.4 Boundary Conditions
The inlet pressure boundary condition of the liquid film between the gear end face friction pairs is determined by simulation. The gear pump pressure cloud map is used to extract the boundary pressure of the left gear and convert it into the inlet pressure boundary of the liquid film. Additionally, appropriate settings for the rotation and stationary walls of the liquid film are made for simulation calculations.
4. Simulation and Modeling
4.1 Modeling and Grid Division
The left gear end face liquid film is selected for simulation analysis. The calculation region is defined with the liquid film’s inner diameter side as the pressure outlet and the outer diameter side as the pressure inlet. The texture is opened on the gear end face, and the upper and lower surfaces of the liquid film are set as rotational and stationary walls, respectively. The Mixture multiphase flow model, SIMPLEC algorithm, and PRESTO format for pressure terms are used for the simulation calculation.
4.2 Grid Independence Verification
To ensure the accuracy and reliability of the simulation results, a grid independence analysis is carried out. The influence of the grid number on the opening force is studied by changing the grid layers in the film thickness direction and the grid size. It is found that using 5 layers of grids for the non – groove area of the liquid film and 9 layers for the groove area can ensure good calculation accuracy and speed. Under these grid layer conditions, further analysis shows that when the grid number reaches about 1.3 million, the opening force stabilizes.
5. Results and Analysis
5.1 Verification of the Simulation Method
The simulation method for the gear end face liquid film is verified by comparing the simulation results with the calculated results in the literature. The pressure radial distribution curves show that the maximum error between the calculated results and the literature results is less than 5%, indicating the accuracy of the simulation method used in this study.
5.2 Pressure and Velocity Field Distributions
5.2.1 Pressure Field
The pressure distribution cloud maps of the liquid film on the gear end face with and without texture are compared. It is found that the maximum pressure of the liquid film on the gear end face with texture is significantly increased. This is because the texture causes a film thickness convergence area, and when the fluid flows into this area at high speed, the pressure increases due to fluid squeezing. The pressure distribution along the circumference of the end face without texture is non – periodic, which causes an obvious overturning moment and exacerbates eccentric wear. In contrast, the texture improves the force balance by increasing the overall film pressure.
5.2.2 Velocity Field
The velocity distribution cloud maps and streamlines of the liquid film on the gear end face with and without texture are compared. The fluid in the liquid film without texture leaks in a spiral line towards the outlet. However, for the gear end face with texture, the fluid flow is guided by the texture pumping direction, and some fluid is pumped upstream due to the presence of the return groove, reducing the end face leakage to some extent.
5.3 Influence of Working Conditions on Lubrication Characteristics
5.3.1 Influence of Film Thickness
The influence of film thickness on the opening force and leakage rate of the liquid film on the gear end face with and without texture is analyzed. With an increase in film thickness, the opening force of the textured end face liquid film first decreases rapidly and then levels off, while the leakage rate first increases slowly and then shows a linear increasing trend. For the non – textured end face liquid film, the opening force hardly changes with film thickness, and the leakage rate increases first slowly and then rapidly. The textured end face liquid film can effectively improve the lubrication performance under the premise of ensuring a small leakage.
5.3.2 Influence of Outlet Pressure
The influence of the gear pump outlet pressure on the opening force and leakage rate of the liquid film on the gear end face with and without texture is studied. With an increase in the outlet pressure, the opening force and leakage rate of both the textured and non – textured end face liquid films increase slowly. Since the influence area of the outlet pressure is mainly the oil discharge area and has little impact on the liquid film pressure boundary, its influence on the opening force and leakage rate and other performance parameters is relatively small.
5.3.3 Influence of Rotational Speed
The influence of the gear pump rotational speed on the opening force and leakage rate of the liquid film on the gear end face with and without texture is investigated. With an increase in the rotational speed, the opening force and leakage rate of the textured end face liquid film increase significantly, while those of the non – textured end face liquid film change little. This is because the non – textured end face does not have a hydrodynamic pressure effect, and the rotational speed has little impact on the non – textured end face film pressure and the leakage rate. For the textured end face, a higher rotational speed enhances the hydrodynamic pressure effect and the pumping effect of the texture, thus affecting the opening force and leakage rate.
5.4 Influence of Structural Parameters on Lubrication Characteristics
5.4.1 Influence of Spiral Groove Depth
The influence of the spiral groove depth on the opening force and leakage rate of the textured end face liquid film is analyzed when the height difference between the spiral groove and the return groove is 0. With an increase in the spiral groove depth, the opening force and leakage rate of the textured end face liquid film first increase rapidly and then level off. Considering the opening and leakage control of the end face liquid film, a suitable range for the spiral groove depth is 7 – 9 µm.
5.4.2 Influence of the Height Difference between the Spiral Groove and the Return Groove
The influence of the height difference between the spiral groove and the return Grove on the opening force and leakage rate of the textured end face liquid film is studied. With an increase in the height difference, the opening force of the textured end face liquid film fluctuates, and the leakage rate decreases. When the height difference is in the range of 5 – 6 µm, the hydrodynamic pressure intensity generated by the 仿 Tesla valve type groove is stronger, and the opening force is larger. Considering the opening and leakage control of the end face liquid film, a suitable range for the height difference is 5 – 6 µm.
5.4.3 Influence of the Inclination Angle of the Elliptical Hole
The influence of the inclination angle of the elliptical hole on the opening force and leakage rate of the textured end face liquid film is analyzed. As the inclination angle increases from – 50° to 0°, the opening force first decreases and then increases, and as the inclination angle further increases, the opening force decreases. The leakage rate continuously decreases as the inclination angle increases. Considering the opening and leakage control of the end face liquid film, a suitable range for the inclination angle is 0 – 10°.
5.4.4 Influence of the Shape Factor of the Elliptical Hole
The influence of the shape factor of the elliptical hole on the opening force and leakage rate of the textured end face liquid film is studied. As the shape factor increases, the opening force and leakage rate of the textured end face liquid film decrease. Considering the opening and leakage control of the end face liquid film, a suitable range for the shape factor within the scope of this study is 0.4 – 0.5.
6. Conclusions
6.1 Importance of Dynamic Pressure Lubrication Textures
The opening of dynamic pressure lubrication textures on the end face not only can effectively open the end face by increasing the fluid film pressure but also can make the pressure distribution more uniform along the circumference, which has a positive effect on improving the stability of the liquid film support and reducing end face eccentric wear.
6.2 Influence of Working Conditions on Textured End Face Liquid Film
Compared with the non – textured gear end face liquid film, working conditions such as film thickness, outlet pressure, and rotational speed have a greater impact on the opening force and leakage rate of the textured end face liquid film. Under high – speed and high – outlet pressure working conditions, the textured end face can ensure better leakage control and lubrication performance of the gear end face friction pairs.
6.3 Optimal Structural Parameters
Within the scope of the calculated working conditions and structural parameters in this study, to ensure that the gear end face friction pairs of high – speed gear pumps have excellent opening and leakage control properties, the spiral groove depth should be in the range of 7 – 9 µm, the height difference between the spiral groove and the return groove should be in the range of 5 – 6 µm, the inclination angle of the elliptical hole should be in the range of 0 – 10°, and the shape factor of the elliptical hole should be in the range of 0.4 – 0.5.
| Parameter | Influence on Lubrication Characteristics | Optimal Range |
|---|---|---|
| Spiral Groove Depth () | Affects opening force and leakage rate | 7 – 9 µm |
| Height Difference between Spiral Groove and Return Groove () | Affects opening force and leakage rate | 5 – 6 µm |
| Inclination Angle of Elliptical Hole () | Affects opening force and leakage rate | 0 – 10° |
| Shape Factor of Elliptical Hole () | Affects opening force and leakage rate | 0.4 – 0.5 |
In conclusion, this study provides a theoretical basis for the design and application of lubrication textures on the gear end faces of high – speed gear pumps, which is beneficial for improving the performance and service life of gear pumps in aviation applications. Future research can focus on further optimizing the texture design and exploring the long – term performance and reliability of the textured gear end face friction pairs under actual working conditions.
7. Future Research Directions
7.1 Long-Term Performance Evaluation
The current study focuses on the lubrication characteristics of the gear end face friction pairs under specific working conditions and structural parameters. However, for practical applications in aviation high – speed gear pumps, it is essential to evaluate the long – term performance of the textured friction pairs. This includes studying the wear behavior of the textures over an extended period, as well as the changes in lubrication performance due to factors such as material degradation and surface roughness evolution. Long – term testing under simulated real – world operating conditions can provide valuable insights into the durability and reliability of the textured gear end face friction pairs.
7.2 Optimization of Texture Design
Although the study has determined the optimal ranges for various texture structural parameters, there is still room for further optimization. Future research could explore more complex texture geometries or combinations of different types of textures to achieve even better lubrication and wear resistance. Additionally, the influence of texture distribution patterns on the end face could be investigated. For example, non – uniform texture distributions or graded textures might offer unique advantages in certain applications. Advanced manufacturing techniques could also be developed to precisely fabricate these optimized textures with high accuracy and reproducibility.
7.3 Multiphysics Coupling Analysis
In real operating conditions, the gear end face friction pairs are subjected to multiple physical phenomena simultaneously, such as fluid – solid coupling, thermal – mechanical coupling, and tribo – chemical reactions. A more comprehensive analysis considering these multiphysics couplings is necessary to accurately predict the performance of the gear pump. For instance, the heat generated due to friction can affect the viscosity of the lubricant and the thermal expansion of the components, which in turn can influence the fluid film thickness and pressure distribution. By developing multiphysics coupling models and conducting simulations, a more accurate understanding of the complex interactions between different physical processes can be achieved, enabling better design and optimization of the gear end face friction pairs.
7.4 Application in Different Gear Pump Designs
The findings of this study are mainly applicable to a specific type of aviation high – speed gear pump. Future research could explore the extension of these texture – based lubrication strategies to other types of gear pumps with different designs and operating requirements. This includes investigating how the texture parameters need to be adjusted for different gear geometries, pump sizes, and flow rates. By adapting the texture design to various gear pump configurations, the benefits of improved lubrication and reduced wear can be widely applied in the field of gear pumps, enhancing their overall performance and efficiency.
8. Experimental Verification
8.1 Experimental Setup
To validate the theoretical findings and simulation results, an experimental setup needs to be designed. This setup should include a test rig capable of operating a gear pump under controlled conditions similar to those in the simulation. The test rig should be equipped with sensors to measure key parameters such as pressure, temperature, and flow rate. Additionally, a mechanism for accurately measuring the wear of the gear end face friction pairs and the performance of the lubricating film should be incorporated. For example, optical microscopy or profilometry techniques could be used to monitor the surface topography of the gear end face and the texture over time.
8.2 Experimental Procedure
The experimental procedure would involve operating the gear pump with and without the textured end face under different working conditions. The measured parameters would be recorded and compared with the theoretical predictions and simulation results. The wear of the gear end face friction pairs would be evaluated at regular intervals to determine the effectiveness of the texture in reducing wear. The lubricating film performance, such as its thickness and stability, would also be assessed. This would involve techniques such as interferometry to measure the film thickness and observing the flow patterns of the lubricant to evaluate its stability.
8.3 Comparison with Theoretical and Simulation Results
The experimental results would be compared with the theoretical and simulation results to validate the accuracy of the models used in the study. If there are discrepancies, further analysis would be required to understand the sources of the differences. This could involve reexamining the assumptions made in the theoretical models, checking the accuracy of the simulation parameters, or investigating any unaccounted – for physical phenomena in the experiments. By ensuring a close match between the experimental and theoretical/simulation results, the reliability of the study’s conclusions can be enhanced, providing more confidence in the application of the texture – based lubrication strategies for gear end face friction pairs.
9. Impact on Aviation Industry
9.1 Improved Gear Pump Performance
The application of the optimized texture design for gear end face friction pairs can significantly improve the performance of aviation high – speed gear pumps. By reducing wear and improving lubrication, the service life of the gear pumps can be extended, reducing maintenance costs and increasing the reliability of the aircraft hydraulic systems. This is crucial for ensuring the safe and efficient operation of aircraft, as any failure in the hydraulic system can have serious consequences.
9.2 Energy Efficiency
Better lubrication and reduced friction in the gear pumps can also lead to improved energy efficiency. With less energy being dissipated due to friction, more of the input power can be converted into useful work, such as pumping hydraulic fluid. This can contribute to reducing the overall energy consumption of the aircraft, which is an important consideration in the context of increasing fuel efficiency and reducing environmental impact.
9.3 Technological Advancements
The research on gear end face friction pair lubrication characteristics represents a technological advancement in the field of aviation gear pumps. It provides a new approach for improving the performance of these critical components, which can inspire further research and development in related areas. This could lead to the development of more advanced gear pump designs and lubrication strategies, ultimately benefiting the entire aviation industry.
10. Conclusion
In this comprehensive study, the lubrication characteristics of gear end face friction pairs in aviation high – speed gear pumps have been investigated. Through theoretical analysis, simulation, and a proposed future experimental verification, important insights have been gained into the behavior of these friction pairs under different working conditions and the impact of texture design on their performance. The optimal structural parameters for the texture have been determined, and directions for future research have been identified. The application of these findings has the potential to significantly improve the performance and reliability of aviation high – speed gear pumps, with positive implications for the aviation industry in terms of cost savings, energy efficiency, and technological advancements. Continued research in this area is essential to further optimize the design and performance of gear end face friction pairs and to ensure the long – term viability and success of aviation gear pump technology.