Analysis of backward whirl characteristics of rubbing dual-rotor systems

Serious rub-impact fault is easy to induce backward whirling of the rotor, which is not conducive to smooth operation. In this paper, the whirl characteristics of a counter-rotating dual-rotor system without rubbing fault, single disk with rub-impact, and multi-disk with rub-impact are analyzed based on the full-spectrum theory. The characteristics and differences of backward whirls caused by unbalanced excitation and rubbing are studied. Besides, a dual-rotor test rig with rub-impact was built, and the rub-impact experiments of the high-pressure rotor (HPR) and low-pressure rotor (LPR) were carried out, respectively. The results show that the frequency component in the full spectrum of backward whirl induced by unbalanced excitation appears as the rotary speed of HPR and LPR. In the backward whirling caused by rubbing, in addition to the frequency component of the unbalanced excitation, there is also a negative backward whirl frequency with a larger amplitude. The main reason for the occurrence of the backward whirl frequency is the alternating positive and negative work of friction. The backward whirl frequency increases gradually with the increase of rotational speed and rubbing stiffness. When there are multiple disks involved in rubbing, the number of backward whirl frequencies will also increase. The above research is helpful to understand the whirling characteristics of rub-impact dual-rotor systems deeply.