Review of rotordynamic characteristics and stability enhancement and vibration suppression techniques of dynamic seals in turbomachinery

Dynamic seals are one of the critical components in modern turbomachinery. Research on related issues such as leakage, heat transfer, aerodynamic excitation, and rubbing failure is of great significance for further improving the operational efficiency and safety stability of turbomachinery. Rotor stability has always been a prominent issue in the design, manufacturing, and operation of turbomachinery, and self-excited vibrations induced by fluid excitation forces from dynamic seals are an important excitation source leading to rotor instability. There is an urgent need to conduct research on the fluid excitation dynamic characteristics and techniques for enhancing stability and suppressing vibrations of dynamic seals, which has important engineering application value for addressing rotor instability issues in modern turbomachinery. This paper introduces damper seal technology in turbomachinery and reviews research progress in experimental measurement methods, numerical prediction methods, and stability enhancement and vibration suppression methods for fluid excitation dynamic characteristics of dynamic seals. Currently, in turbomachinery, the typical dynamic sealing technologies widely used include non-contact dynamic seals such as labyrinth seals, honeycomb damper seals, hole-type damper seals, pocket damper seals, helical groove seals, etc., and contact dynamic seals such as brush seals and finger seals, etc. Compared to traditional labyrinth seals, damper seals improve the fluid excitation dynamic characteristics and increase seal damping by altering the smooth stator surface structure to achieve greater roughness. Currently, widely used damper seals in engineering include honeycomb damper seals, hole-pattern damper seals, and pocket damper seals. The study of rotordynamic characteristics of dynamic seals primarily involves experimental testing and numerical simulation methods to obtain eight rotordynamic characteristic coefficients of the dynamic seal under different operating conditions and geometric parameters, and to evaluate the impact of the dynamic seal on the vibration modes, critical speeds, and dynamic stability of the rotor system. There are two research methods for studying the rotordynamic characteristics of dynamic seals: experimental measurement and numerical prediction. Based on the differences in measurement methods, measured variables, and identification methods of rotordynamic coefficients in experimental research, experimental methods can be divided into three types: (1) system mechanical impedance method. Depending on the excitation source, the system mechanical impedance method is further divided into the impact excitation mechanical impedance method and the harmonic excitation mechanical impedance method. (2) Dynamic cavity pressure response method. (3) Static force-deflection method. Among these, the static force-deflection method is often used to verify the accuracy of the measurement results from the first two experimental methods. There are four numerical prediction methods: (1) bulk flow model; (2) ‘3D steady-state’ CFD method; (3) single-frequency perturbation “3D transient-state” CFD method; (4) multi-frequency perturbation “3D transient-state” CFD method. The harmonic-excitation mechanical impedance method and the multi-frequency perturbation numerical method are advanced experimental measurement and numerical prediction techniques, respectively, for the study of fluid excitation dynamic characteristics of dynamic seals. The techniques for enhancing stability and suppressing vibrations in dynamic seals, such as damper seal technology, anti-swirl technology, and divergent/convergent seal clearance method, hold significant engineering application value for addressing rotor vibration instability issues in turbomachinery. Finally, the research prospects for uncertainty quantification and robust optimization design of the actual service performance of dynamic seals in turbomachinery are discussed.