Nonlinear Modal Analysis of Frictional Ring Damper for Compressor Blisk

Blisk is described as a single-piece rotating bladed-disk instead of an assembly. It consists of a single disk with several blades. The use of integrally blisk is becoming popular because of advantages in aerodynamic efficiency and mass reduction. However, in integrally blisk structures, there are no friction interfaces leading to a low structural damping compared to assembled bladed-disk. In some extreme cases, high vibration response of integrally blisk can lead to high cycle fatigue, which is regarded as a common reason for compressor failure. One emerging damping-technique to enhance the damping of the integrally blisk is on the use of friction ring damper which exploits the frictional energy dissipation at the contact interface. The ring damper is located in the groove of the host disk and is hold in contact with the blisk by the centrifugal forces.

In this paper, an efficient methodology to design the frictional ring damper for an integrally blisk is described. This methodology is based on nonlinear modal analysis with energy balancing method that enables to directly compute the energy dependent modal and damping properties of different ring damper configurations. The concept of extended periodic motion is used in nonlinear modal analysis. The energy balancing method is used to relate the nonlinear modal property to the system with forced excitation. The nonlinear dynamic analysis is achieved by numerical solver based on multi-harmonic balance method and continuation technique.

A full-scale compressor blisk is used as the test case where the integrally blisk and ring damper are modelled in a sector with cyclic symmetric boundary conditions. The contact friction forces are modelled based on 3D Jenkins element and a general Craig-Bampton reduced order modelling technique is used to reduce the computational cost. A nonlinear static analysis is performed first to get the static equilibrium as well as the normal pressure distribution at the contact interface between the ring damper and the blisk. The nonlinear vibration response is then determined around this static equilibrium. The damping performance for different ring dampers are evaluated and compared. Energy dissipation is also investigated with respect to nonlinear modes. This nonlinear modal analysis demonstrates the damping ability of the ring damper for integrally blisk. The initial results show that the frictional ring damper can dissipate the vibration energy for those modes with strong blade-disk coupling effect. Vibration level of the blisk can be damped significantly. This modelling strategy based on nonlinear modal analysis can be considered as an efficient methodology to design a frictional ring damper and some guidelines are given for the design of the ring damper for integrally blisk.