Oil film analysis and axial uniform distribution optimization for the sliding bearing in GTF engines

The journal bearings of planetary gear are the key technologies of the gearbox in geared turbo fan engine(GTF). GTF journal bearings are usually operated under high-speed, heavy-load, and large-eccentricity conditions. The harsh operating conditions results in high oil temperature and thermal deformations, non-uniform oil film thickness, journal inclination, and furtherly increase the failure risks. To improve the service life and operating safety of GTF journal bearings, the performance parameter of axial physical field homogenization was defined. The performance characteristics of GTF journal bearing were studied based on the thermal-elastohydrodynamic lubrication method under high-speed, heavy-load, and large-eccentricity conditions. The influence of journal inclination and thermal effect was included. The performance comparisons were conducted under various working conditions for journal bearings with four different journal profile, which were defined as R-profile, L-profile, convex profile, and linear profile. The effect of different journal profile on the bearing performance are studied. The performance of R-profile journal bearing is selected out and optimized by multi-objective optimization. The results indicated that the performance characteristics can be improved by the design of axial journal profile. The positive influence can be obtained with the increase of journal eccentricity and rotating speed. Besides, the improvement of R-profile journal bearing is the most significant, especially when considering the influence of journal inclinations. Then, the axial physical field homogenization, load carrying capacity, and oil film temperature were selected as optimization objectives. The multi-objective optimizations were carried out based on genetic algorithm for R-profile journal bearing. The bearing performance were significantly improved resulting from the optimization, which considering the influence of axial physical field homogenization. This study provides valuable guides for design of GTF journal bearings with high load carrying capacity and high performance reliability.