Effect of planetary gearboxes on the dynamics of rotating systems

Abstract

The coupled dynamic behaviour of planetary geared rotor systems is much less well understood compared to the classical geared rotor systems. For a better understanding, this research project investigates the coupled dynamic behaviour of planetary geared rotor systems and how the planetary gearbox parameters affect their global dynamics. In the numerical study, a six degrees of freedom hybrid dynamic model of a planetary geared rotor system is created in the recently developed “GEAROT” rotor dynamics software by considering gyroscopic effects. Based on the modal analysis results of the hybrid dynamic model, the vibration modes are classified as coupled torsional-axial, lateral and gearbox for the helical gear configuration, and torsional, axial, lateral and gearbox for the spur one. Modal energy analysis is used to quantify the coupling level between the shafts and planetary gearbox, which highlights the effect of a planetary gearbox on the dynamic behaviour of a rotating system. An extensive planetary gearbox parameter study including gear contact, gearbox mass and support, and planet gear parameters is conducted using the hybrid dynamic model to investigate the parameter effects on the modal behaviour of planetary geared rotors. The sensitivity of planetary geared rotor vibration modes to the gearbox parameters is determined by computing the frequency shifts and comparing the mode shapes between the two extreme cases. In the experimental study, free-free impact hammer tests are carried out on a planetary geared rotor assembly to validate the numerical modal analyses results in “GEAROT”. On the basis of both experimental and numerical modal analysis of planetary geared rotors, the lateral vibration modes are identified as “in phase” and “out of phase”. Briefly, the numerically identified lateral modal behaviour of planetary geared rotor systems is successfully validated with the experimental modal analysis results.