Dynamics research on the rubbing process and rubbing forms of rotor–blade–casing​ systems

Rubbing is a common phenomenon in aero engines. Serious rubbing will cause failure, and even lead to accidents. Blade–casing rubbing is complicated, the rubbing process, rubbing positions, and rubbing forms are important factors to describe the rubbing of blade and casing. The details of these problems are lacking in published works. This paper aims to gain insight into the process and characteristics of blades participating in rubbing and propose an experimental method for quantitatively judging the blades with rub-impact faults. Firstly, a rotor–blade–casing dynamic model with the consideration of the flexibility of blades is established. After that, using Poincaré sections and bifurcation diagrams of the rotor, the influence of the number of blades involved in rubbing on the motion behavior of the rotor is discussed. Then, the process of the blades participating in the rubbing, the rubbing forms, and rubbing positions under the speed-up condition are analyzed. Besides, the influence of the gravity of the system on the rubbing process and the motion state of the rotor is analyzed. Finally, a test rig with four blades is built. Based on the strain signals of four blades, an evaluation index that can quantitatively judge the blades involved in rubbing is defined to verify the complex rubbing process. The results show that the rubbing between blades and casing will undergo complex rubbing forms; different forms of rubbing have different rubbing parts; the number of blades involved in rubbing will affect the motion behavior and the smooth operation of the rotor system. This research can provide some reference for rubbing fault diagnosis in engineering. •The rotor–blade–casing system will experience a complex rubbing process and rubbing patterns when speeding up.•Under the influence of gravity, the rubbing positions of different rubbing patterns are different.•The number of blades participating in rubbing will affect the motion behavior and the smooth operation of the system.•Based on the strain signal, a quantitative index Vϵ is proposed to judge whether the blade rubs or not.