Influence of the Impact of Velocity on Oil Injection Lubrication Flow Field and Temperature Field in High-Speed Aeronautical Bevel Gears

The gear transmission system in aircraft engines often operates under high-speed and heavy-load conditions. Reliable lubrication is crucial to ensure that the spiral bevel gears do not experience gear scuffing or pitting. In aircraft accessory gearboxes, spiral bevel gears often rely on oil jet lubrication. However, the oil spray parameters designed empirically do not consider the lubrication degradation caused by jet breakup due to rotational speed, making it difficult to meet the design requirements of aircraft gear transmission. A Finite Volume-based thermal-fluid coupling simulation model of spiral bevel gears has been established to consider the influence of actual conditions such as gear speed, oil spray velocity, spray angle on lubrication and heat dissipation effects, supporting the high-reliability and high-power density design of aircraft gear transmission. The model investigated the flow field and temperature field where the velocity of the gear reached up to 160 m/s. It comprised modules for analyzing the lubrication flow field of gear oil spray and calculating the temperature field of the gear. The Dynamic Mesh method with Global Remeshing approach was used to simulate the rotation of gears in the flow field, and the RNG k-\varepsilon model with higher accuracy was employed to analyze turbulence for high rotational flow. The standard wall functions were used to analyze the distribution of oil on the gear surface. Stability checks and mesh independence checks were conducted to confirm the reliability of the results. The flow field analysis module provided parameters such as the gear tooth surface oil volume fraction, wall heat transfer coefficient, and windage loss. The comprehensive viscosity was employed to correlate gear lubrication with gear oil-air ratio, combined with meshing loss of spiral bevel gears under oil jet conditions to compute frictional heat flow at different linear velocities. Considering multiple heat sources such as heating from windage and meshing heat generation, and multiple heat dissipation channels including convective heat transfer and thermal conduction, the temperature distribution of the gear was determined. By comparing the differences in aerodynamic drag loss calculations between NASA experiments, empirical formulas, and the model, the accuracy of the model was validated. The model analysis revealed that as the gear velocity increased from 40 m/s to 160 m/s, the jet breakup offset phenomenon intensified, leading to an 83.5% decrease in the average oil-air ratio on the gear surface. The lubricating oil significantly affected convective heat transfer on the gear surface, with a sharp increase in the wall heat transfer coefficient at the gear oil jet location. As the velocity increased, the rising trend of convective wall transfer coefficient in the meshing zone shifted to a decreasing trend after 120 m/s, indicating deteriorating lubrication heat transfer conditions. With the increase in velocity, windage loss exhibited a nearly exponential growth pattern. The windage loss accounts for over 80% of the total loss at 160 m/s, becoming the primary source of loss at high gear speeds and resulting in reduced transmission efficiency.