Dynamic Characteristics Analysis of Flexible Rotor System With Pedestal Looseness

Due to the limitation of assembly conditions and working load environment, the design of pedestal looseness is often used in the structural design of aeroengine multi support flexible rotor, which affects the vibration response and stability of the rotor system. In this paper, a dynamic model of a flexible rotor system with pedestal looseness is established for a practical aeroengine flexible rotor system. Next, a nonlinear modal analysis process for the multi degree of freedom nonlinear rotor system is proposed. Based on this, the nonlinear modal characteristics of the flexible rotor system with pedestal looseness are analyzed. An interval prediction method of modal damping interval for stability analysis of rotor system is presented, and the influence of key characteristic parameters on modal damping and vibration stability of rotor system is explored. Finally, the vibration characteristics of the rotor system are obtained by numerical integration method. The results show that the modal characteristics of the rotor vary with the amplitude of the rotor, and have the feature of interval distribution; vibration stability mainly depends on tangential friction and additional lateral constraint; when the amplitude of the rotor is large, the backward whirling motion may occur and the vibration may be unstable. This paper will provide a theoretical method for dynamic optimization of multi support flexible rotor system, which is helpful to ensure the reliability and safety design of aeroengine.

Nonlinear Modal Analysis of Frictional Ring Damper for Compressor Blisk

The use of integrally blisk is becoming popular because of the advantages in aerodynamic efficiency and mass reduction. However, in an integrally blisk, the lack of the contact interface leads to a low structural damping compared to an assembled bladed-disk. One emerging damping technique for the integrally blisk is based on the use of friction ring damper which exploits the contact interfaces at the underneath of the disk. In this paper, three different geometries of the ring dampers are investigated for damping enhancement of a blisk. A full-scale compressor blisk is considered as a case study where a node to node con- tact model is used to compute the contact forces. The dynamic behaviour of the blisk with the ring damper is investigated by using nonlinear modal analysis which allows a direct estimation of the damping generated by the friction interface. The damping performance for the different ring dampers are evaluated and compared. It appears that the damping efficiency as well as the shift in the resonant frequency for the different geometries are highly related to the nodal diameter and contact pressure/gap distributed within contact interface. The geometry of the ring damper has significant impact on the damping performance.

Investigating the Influence of Fluid-Structure Interactions on Nonlinear System Identification

A complex fluid-structure interaction can often create nonlinear dynamic behaviour in the structure. This can be better estimated using nonlinear modal analysis, capable of identifying and quantifying the nonlinearity in the structure. In this study, the case of a vibrating beam submerged in liquid using a nonlinear parameter identification method is presented. This system is considered as an alternative propulsion mechanism, hence understanding the interaction between the fluid and the structure is necessary for its control. Here, impulse signals are used to characterise the numerical and experimental dynamics response of the system. Since the transient responses contain of a multi-component vibratory signals, a vibration decomposition method is used to separate the time response signals based on the dominant amplitude in the frequency response function. The separated time-series signals are then fitted to the nonlinear identification method to construct the backbone and damping curves. The modal parameters obtained from experimental data are then used as a base for the development of the analytical models. The analytical approaches are based on the Euler-Bernoulli beam theory with additional mass and quadratic damping functions to account for the presence of the fluid. Validations are carried out by comparing the dynamic responses of the analytical and experimental measurements demonstrating the accuracy of the model and hence, its suitability for control purposes.

Nonlinear Modal Analysis of Frictional Ring Damper for Compressor Blisk

The use of integrally blisk is becoming popular because of the advantages in aerodynamic efficiency and mass reduction. However, in an integrally blisk, the lack of the contact interface leads to a low structural damping compared to an assembled bladed-disk. One emerging damping technique for the integrally blisk is based on the use of friction ring damper which exploits the contact interfaces at the underneath of the disk. In this paper, three different geometries of the ring dampers are investigated for damping enhancement of a blisk. A full-scale compressor blisk is considered as a case study where a node to node contact model is used to compute the contact forces. The dynamic behaviour of the blisk with the ring damper is investigated by using nonlinear modal analysis which allows a direct estimation of the damping generated by the friction interface. The damping performance for the different ring dampers are evaluated and compared. It appears that the damping efficiency as well as the shift in the resonant frequency for the different geometries are highly related to the nodal diameter and contact pressure/gap distributed within contact interface. The geometry of the ring damper has significant impact on the damping performance.