Research on coupled angular-torsional vibration of unbalanced rotor

Bending-torsional coupling of unbalanced rotor may lead to combined resonance or dynamic instability in rotor systems, potentially compromising system operation. Existing studies on bending-torsional coupling often rely on rotor models that consider only lateral and torsional vibrations, neglecting the influence of pitch vibration and gyroscopic effect in flexible rotors. For this reason, the present study first develops a 3-DOF unbalanced rotor dynamic model with angular and torsional DOFs. The analysis identifies two distinct types of coupling terms in the dynamic equations that have a significant impact: periodically time-varying parameter terms and cross-multiplicative coupling terms, which are shown to induce frequency-modulated coupling between angular and torsional vibrations. Subsequently, a method for calculating the mode and forced response of the rotor is proposed. The results reveal that the gyroscopic effect tends to narrow the instability region. Finally, dedicated angular-torsional coupling instability experiments are performed, confirming the theoretical predictions.