Study on Dynamic Characteristics of Single-Span Rotor Under Cross-Coupling Stiffness Control on Nondrive End

Abstract

The sealing-induced cross-coupling stiffness (CCS) often decreases the rotordynamic stability of turbomachinery. In our previous study, an active negative CCS control strategy applied between two bearings in the middle of the rotor was validated to enhance the stability of the rotor system. In this paper, a different approach was taken by applying both positive and negative CCS control strategies to the nondrive end, aiming to investigate their effects on rotordynamic stability using a rotordynamic model. The model represented a single-span centrifugal compressor rotor with CCS at the seal node. The logarithmic decrements and unbalance response of the rotor system were compared under different CCS applications at the nondrive end and in the span. The results demonstrate that applying both positive and negative CCS at the nondrive end can improve system stability, but the positive CCS strategy has limitations, and its applicability is not as extensive as negative CCS. A “critical stiffness” phenomenon emerges when the rotor system is actively stabilized at the nondrive end, resembling critical resonance. Furthermore, when components like seals introduce cross-coupling stiffness out of the span, they contribute to system stabilization. These findings provide valuable insights into actively enhancing the stability of rotor systems.