1. Introduction
Gear pumps play a crucial role in various industries, especially in aviation where reliability and performance are of utmost importance. The circular arc oscillating internal gear pump has gained significant attention due to its unique design and advantageous characteristics. This article focuses on the numerical analysis of the performance of such pumps under different operating conditions, specifically in the context of aviation applications.
1.1 Background
In aviation systems, gear pumps are used for tasks such as lubrication and fuel transfer. The circular arc oscillating internal gear pump stands out for its simplicity, smooth operation, low noise, long lifespan, good speed characteristics, and high volumetric efficiency. However, in practical applications, factors such as gas dissolution and release in the lubricating oil can affect its performance. Understanding these factors and their impact on the pump’s performance is essential for optimizing its design and operation.
1.2 Research Objectives
The primary objective of this study is to analyze the performance of the circular arc oscillating internal gear pump for aviation under gas-liquid two-phase conditions. Specifically, we aim to investigate the effects of different operating speeds, end clearances, rotor stages, and rotor thicknesses on the volumetric efficiency of the pump. By doing so, we hope to provide valuable insights for the design and optimization of these pumps in aviation applications.
2. Gear Pump Structure and Working Principle
2.1 Structure
The circular arc oscillating internal gear pump typically consists of an inner rotor, an outer rotor, front and rear end covers, an eccentric sleeve, and a pump housing. The inner rotor has a tooth profile that is an equidistant curve of a continuous short-amplitude epicycloid, while the outer rotor uses a circular arc as its conjugate tooth profile curve.
2.2 Working Principle
As the inner rotor rotates, it drives the outer rotor to rotate in a coordinated manner. The meshing of the teeth creates a series of sealed chambers that change in volume as the rotors turn. This volume change causes the fluid (in this case, a mixture of oil and gas) to be drawn in and then pumped out of the pump.
3. Numerical Simulation Methods
3.1 Control Equations
To accurately model the fluid flow within the gear pump, we use a set of control equations. The continuity equation and the momentum conservation equation are used to describe the fluid motion. Here, is the mixed density, represents the velocity in the direction, is the pressure, and is the dynamic viscosity coefficient of the mixed phase.
3.2 Two-Phase Flow VOF Model
The Volume of Fluid (VOF) model is employed to handle the gas-liquid two-phase flow. This model tracks the interface between the two phases by using the volume fraction of each phase in the grid cells. In each grid cell, the sum of the volume fractions of the gas and liquid phases is equal to 1.
3.3 Turbulence Model
The Reynolds time-averaged turbulence model is used due to its simplicity, stability, accuracy, and wide applicability. The equations for turbulent kinetic energy and the dissipation rate are used to account for the turbulent nature of the fluid flow within the pump.
3.4 Computational Model and Boundary Conditions
A specific circular arc oscillating internal gear pump used for aviation lubricating oil return is selected as the research object. The computational domain three-dimensional model is obtained through Boolean operations, which retains the geometric details of the pump’s flow channel. The inlet and outlet sections of the flow channel are considered as stationary domains, while the flow channel between the inner and outer teeth is a rotating domain. Appropriate boundary conditions are set for the inlet, outlet, and walls of the pump.
3.5 Computational Grid and Conditions
The software Pumplinx is used to divide the computational grid of the gear pump. The stationary domain is divided using a general grid division module, and the rotating domain is divided using a RTM grid division module for dynamic grid generation. After a grid independence analysis, a suitable grid number is selected for the numerical simulation. The SIMPLC algorithm is used to couple the pressure and velocity, and the Multiphase model is called to handle the gas-liquid two-phase flow. The rotor rotation is divided into time steps, and the last cycle’s average outlet flow is analyzed for accuracy.
4. Results and Analysis
4.1 Effect of Rotational Speed on Volumetric Efficiency
| Inlet Oil Volume Fraction (IOVF) | Rotational Speed vs. Volumetric Efficiency Relationship |
|---|---|
| 30% | As speed increases from 5000 r/min, volumetric efficiency first increases and then decreases. |
| 40% | Similar trend as 30%, but the turning point may vary. |
| 50% | Volumetric efficiency change is more pronounced as speed increases. |
| 60% | At higher speeds, volumetric efficiency starts to decrease more significantly. |
| 70% | Largest decrease in volumetric efficiency as speed increases, with a maximum reduction of 27.29%. |
When the IOVF is low, the volumetric efficiency of the gear pump first increases and then decreases with the increase in rotational speed. This is because at low speeds, the oil has not filled the cavities between the inner and outer rotors completely. As the speed increases, the centrifugal force of the oil increases, allowing it to fill the cavities better, and the gas compressibility also contributes to an increase in the oil flow. However, as the speed continues to increase, the filling time shortens, and the increase in oil flow becomes less significant. When the IOVF is high, the volumetric efficiency decreases with the increase in rotational speed because the compressible gas volume is relatively small, and the oil flow reaches a threshold at a certain speed.
4.2 Effect of End Clearance on Volumetric Efficiency
| Inlet Oil Volume Fraction (IOVF) | End Clearance vs. Volumetric Efficiency Relationship |
|---|---|
| 30% | Volumetric efficiency decreases as end clearance increases. |
| 70% | Similar trend as 30%, but the decrease is less pronounced as IOVF increases. |
Under different IOVF conditions, the volumetric efficiency of the gear pump decreases as the end clearance increases. This is because an increase in end clearance leads to more end face leakage, reducing the oil flow while the theoretical flow remains unchanged, thus resulting in a lower volumetric efficiency.
4.3 Effect of Rotor Stage on Volumetric Efficiency
| Inlet Oil Volume Fraction (IOVF) | Rotor Stage vs. Volumetric Efficiency Relationship |
|---|---|
| 30% | Volumetric efficiency decreases as rotor stage increases. |
| 70% | Volumetric efficiency increases as rotor stage increases. |
When the IOVF is low, the volumetric efficiency of the gear pump is negatively correlated with the increase in rotor stage. This is because an increase in rotor stage may lead to more internal leakage or other factors that reduce the volumetric efficiency. When the IOVF is high, the volumetric efficiency is positively correlated with the increase in rotor stage. This may be due to an improvement in the oil filling and distribution within the pump as the rotor stage increases, especially when the IOVF is relatively high.
4.4 Effect of Rotor Thickness on Volumetric Efficiency
| Inlet Oil Volume Fraction (IOVF) | Rotor Thickness vs. Volumetric Efficiency Relationship |
|---|---|
| 30% | Volumetric efficiency decreases as rotor thickness increases. |
| 70% | Volumetric efficiency decreases more significantly as rotor thickness increases. |
Under different IOVF conditions, the volumetric efficiency of the gear pump decreases as the rotor thickness increases. As the rotor thickness increases, the cavity volume between the inner and outer rotors increases, and the end face leakage relatively decreases, initially causing an increase in the oil flow. However, as the rotor thickness continues to increase, the centrifugal force of the oil does not change due to the constant rotational speed, and the oil cannot fill the cavities effectively, resulting in a decrease in the volumetric efficiency.
5. Discussion
5.1 Comparison with Previous Studies
Previous studies on gear pumps have mainly focused on single-phase conditions or other aspects such as flow characteristics and geometric parameters. This study extends the research to gas-liquid two-phase conditions and comprehensively analyzes the effects of multiple factors on the volumetric efficiency of the circular arc oscillating internal gear pump. The results provide a more complete understanding of the pump’s performance under practical operating conditions.
5.2 Practical Implications
The findings of this study have important practical implications for the design and operation of circular arc oscillating internal gear pumps in aviation. For example, when designing the pump, the appropriate rotor speed, end clearance, rotor stage, and rotor thickness can be selected based on the expected operating conditions and the required volumetric efficiency. During operation, the pump can be optimized by adjusting these parameters according to the actual gas-liquid ratio and other factors.
6. Conclusion
In this study, a numerical analysis of the performance of circular arc oscillating internal gear pumps for aviation under gas-liquid two-phase conditions was conducted. The effects of rotational speed, end clearance, rotor stage, and rotor thickness on the volumetric efficiency were investigated. The main conclusions are as follows:
- The volumetric efficiency of the gear pump is affected by the rotational speed in different ways depending on the inlet oil volume fraction. At low IOVF, it first increases and then decreases with speed, while at high IOVF, it decreases with speed.
- The volumetric efficiency decreases as the end clearance increases under different IOVF conditions.
- The relationship between the volumetric efficiency and the rotor stage is negative when the IOVF is low and positive when the IOVF is high.
- The volumetric efficiency decreases as the rotor thickness increases under different IOVF conditions.
These findings provide valuable guidance for the design and optimization of circular arc oscillating internal gear pumps in aviation applications, helping to improve their performance and reliability. Future research could focus on further exploring the interaction between different factors and developing more accurate models for predicting the pump’s performance under complex operating conditions.
7. Future Research Directions
7.1 Complex Operating Conditions
In real aviation applications, gear pumps often operate under more complex conditions than those studied in this research. Future studies could consider additional factors such as varying temperatures, pressures, and fluid viscosities. These factors can have a significant impact on the performance of the gear pump and need to be incorporated into the analysis for a more comprehensive understanding.
7.2 Wear and Tear
The long-term performance of gear pumps is also affected by wear and tear. As the pump operates over time, the components may experience abrasion, fatigue, and other forms of degradation. Research on how these factors influence the volumetric efficiency and overall performance of the pump would be valuable. This could involve developing models to predict the rate of wear and its consequences on the pump’s operation.
7.3 Optimization Algorithms
With the increasing demand for high-performance gear pumps, there is a need for more efficient optimization algorithms. These algorithms could be used to find the optimal combination of design parameters (such as rotor speed, end clearance, rotor stage, and rotor thickness) to achieve the highest volumetric efficiency under given operating conditions. Research in this area could focus on developing novel optimization techniques and comparing their performance with existing methods.
8. Design Considerations for Aviation Gear Pumps
8.1 Material Selection
The materials used in the construction of aviation gear pumps must be carefully chosen to withstand the harsh operating conditions. They should have high strength, good wear resistance, and be compatible with the fluids being pumped. For example, in the case of lubricating oil pumps, the materials should not react with the oil and should be able to maintain their mechanical properties at high temperatures and pressures.
8.2 Manufacturing Tolerances
Precise manufacturing tolerances are crucial for the proper functioning of gear pumps. Tight tolerances ensure that the components fit together accurately, minimizing leakage and maximizing efficiency. However, achieving very tight tolerances can be challenging and costly. Future research could explore ways to optimize manufacturing tolerances to balance performance and cost.
8.3 Integration with Aircraft Systems
Aviation gear pumps are an integral part of the aircraft’s overall system. They need to be designed to integrate seamlessly with other components such as engines, fuel systems, and lubrication systems. This requires a thorough understanding of the interfaces and interactions between different systems and careful consideration of factors such as flow rates, pressures, and control mechanisms.
9. Performance Evaluation in Real Aviation Environments
9.1 Field Tests
To validate the numerical results obtained in this study, field tests in real aviation environments are essential. These tests could involve installing the gear pumps on actual aircraft and monitoring their performance over a period of time. The data collected from these tests could be used to compare with the numerical predictions and to identify any discrepancies or areas for further improvement.
9.2 Instrumentation and Data Acquisition
Accurate instrumentation and data acquisition are necessary for evaluating the performance of gear pumps in real environments. Sensors need to be installed to measure parameters such as flow rates, pressures, temperatures, and volumetric efficiencies. The data collected should be reliable and accurate to provide a true picture of the pump’s performance.
9.3 Data Analysis and Interpretation
Once the data is collected, it needs to be analyzed and interpreted properly. Statistical methods could be used to analyze the data and identify trends and patterns. The results of the data analysis could be used to make informed decisions about the design and operation of the gear pumps.
10. Economic and Environmental Considerations
10.1 Cost-Effectiveness
The design and operation of aviation gear pumps should also take into account economic factors. The cost of manufacturing, installation, and maintenance of the pumps should be minimized while still ensuring high performance. This requires a careful balance between performance and cost, and may involve exploring alternative materials, manufacturing processes, and maintenance strategies.
10.2 Environmental Impact
In today’s environmentally conscious world, the environmental impact of aviation gear pumps should also be considered. This includes factors such as energy consumption, emissions, and the potential for fluid leakage. Designing pumps that are more energy-efficient and have lower emissions can contribute to reducing the environmental footprint of aviation operations.
11. Conclusion
This article has provided a comprehensive numerical analysis of the performance of circular arc oscillating internal gear pumps for aviation under gas-liquid two-phase conditions. The effects of various factors on volumetric efficiency have been investigated, and practical implications for design and operation have been discussed. Future research directions have been identified, including considerations for complex operating conditions, wear and tear, optimization algorithms, and more. Additionally, design considerations for aviation gear pumps, performance evaluation in real environments, and economic and environmental considerations have been explored. By addressing these aspects, it is hoped that the performance and reliability of aviation gear pumps can be further improved, contributing to the overall efficiency and safety of aviation operations.