Co-Axial Rotor Aero-Engine System: A Hybrid Modeling and Dynamic in Situ Residual Balancing Between High and Small Frequencies Along Simulated Trial Unbalances With Active Magnetic Bearing Integration

Imbalance is a synchronous vibration and is observed at the 1× (synchronous vibration). In this study, the dynamic in-field balancing of the coaxial rotor aero-engine system, that is, the estimation of the residual imbalance, is considered with the active magnetic bearing (AMB) integration. AMB devices are built with a feedback control algorithm with a proportional-integral-derivative (PID) control. The improved influence coefficient method (IICM) is used to identify imbalance forces in low and high-pressure rotors simultaneously through simulated trial unbalance from AMB magnetic excitation. To estimate the imbalances using IICM, the system's vibratory responses in the limited regions and the simulated trial unbalances' phase and magnitudes are only needed. The coaxial-rotor system's differential equation and dynamic model are established with a squeeze-film damper (SFD) at a low-pressure rotor using force coefficients in linear form. A flexible roller bearing, including an intershaft flexible bearing (IFB), supports the high-pressure rotor at both ends accordingly. For a mathematical model, the displacement response from a coaxial rotor aero-engine with discrete unbalances for multidisk and multiplane configurations is established to illustrate the proposed technique by a finite element method (FEM). To validate the proposed technique, a specific percentage from measurement noises is considered while estimating the residual imbalances. It is found that the coaxial rotor system can smoothly cross its critical speed with minimal vibrational response upon balancing.