The accessory gearbox of an aero-engine operates under high-speed and heavy-load conditions, where insufficient lubrication may lead to oil-film failure, increased frictional losses, and reduced transmission reliability. Therefore, understanding oil-jet injection and tooth surface oil-film spreading characteristics is essential for improving lubrication performance. In this study, a three-dimensional geometric model incorporating the meshing region and oil nozzles was established based on a typical accessory gear pair. The model employs the VOF multiphase flow approach and the standard k-ε turbulence model, coupled with dynamic mesh techniques to accurately capture the transient interactions between gear rotation and oil–air two-phase flow. Numerical simulations reveal the dynamic evolution of oil injection, impingement on the tooth surface, oil-film spreading, and transport into the meshing zone, while the effects of injection velocity and nozzle length on lubrication performance are quantitatively analyzed. Results indicate that an injection velocity of 45–55 m/s yields optimal oil-film coverage and uniformity, and a nozzle length of h = 30 mm minimizes jet energy decay and airflow interference, achieving uniform oil filling in the meshing zone. The optimal lubrication performance for accessory gears is obtained at an injection velocity of 45–55 m/s and a nozzle length of 30 mm. This study provides a reference for the design optimization of accessory gear lubrication systems.

The dynamic pressure oil-air separator plays a vital role in aero-engine lubrication systems, as its performance directly determines overall reliability and efficiency. To enhance lubrication performance, it is essential to understand the internal flow characteristics within the separator. In this study, a Mixture multiphase flow model was employed to numerically investigate the oil-air two-phase flow field inside the separator. The effects of inlet velocity and initial oil-air ratio on the distributions of air phase, tangential velocity, and axial velocity were systematically analyzed to elucidate the correlation between flow field structure and separation performance. Numerical results indicate that the tangential velocity distribution conforms to a Rankine vortex structure: a forced vortex exists in the central region, while a free vortex forms near the wall. Axial velocity is negative near the central axis, indicating air motion toward the outlet, and positive near the wall, representing oil motion toward the bottom. At an initial oil-air ratio of 7:3, increasing the inlet velocity from 3.5 to 4.5 m/s stabilizes the internal swirling flow and mitigates air accumulation at the bottom, raising separation efficiency from 90.7% to a maximum of 93.9%. Moreover, a higher initial oil-air ratio facilitates a stable, continuous oil film along the wall, suppressing turbulent interphase mixing. Consequently, at 4.0 m/s, increasing the ratio from 7:3 to 8:2 further enhances efficiency from 92.5% to 93.3%. Numerical predictions agree well with experimental data, with a maximum error of 6%.