Hybrid Elastohydrodynamic Lubrication Modeling and Ultrasonic Inversion of Bearing Film Thickness in UAV Transmission System

In this study, a hybrid elastohydrodynamic lubrication model and ultrasonic inversion method are combined to propose a film thickness prediction framework for UAV rotor bearings. Firstly, a mixed elastohydrodynamic lubrication mathematical model was established based on the two-dimensional Reynolds equation, and the finite difference and relaxation iteration methods were introduced to obtain the film thickness and pressure distribution considering wear and surface roughness. Then, the spring layer model was built based on the ultrasonic reflection theory. Combined with the mathematical relationship between the amplitude of ultrasonic reflection coefficient and the stiffness of lubricating layer, the non-contact inversion analytical formula of oil film thickness was derived. By comparing the numerical simulation results with the ultrasonic inversion results, it is found that they are highly consistent in the film thickness distribution trend, which verifies the reliability of the method. This study provides theoretical and technical support for the real-time monitoring and prediction of bearing lubrication status of UAV, and has application value for improving the dynamic performance and engineering safety of transmission system.