Simulations of Friction Damping on Laboratory-Test-Rigs of Rotors and Stators of an Axial Compressor

Abstract

This paper presents comparisons of the non-linear behaviours and the damping characteristics of rotors and stators. It assesses the differences between the linear FE predicted modeshapes and the measured operating deflection shapes (ODS) of rotors and stators of an axial compressor. The comparisons are between the experimental results obtained from the laboratory rig damping tests and the numerical nonlinear forced response analyses. The damping tests are performed using an experimental rig apparatus driven by piezoelectric and electromagnetic shakers. The forced response analyses are performed on the finite element (FE) models that simulate the laboratory rig configurations using in-house multi-harmonic balance non-linear forced response code named FORSE. Firstly, the measured resonant frequencies and ODS are compared against the predicted results. Moreover, some comparisons of the damping characteristics and local interactions at friction interfaces are discussed. Then, the FORSE predicted instantaneous displacements are examined to understand possible changes in ODS using the Modal Assurance Criterion (MAC) technique. It was found that the instantaneous displacements predicted by FORSE are significantly different from the modeshapes predicted by the linear FE tool. These results suggest that the experimentally measured ODS of the components may also differ from linear FE results. The predicted normalised maximum alternating stresses are also shown to be different from the standard linear FE results due to the modal coupling effects between the neighbouring modes. These findings should alert the engineers about the possibilities of misinterpreting component vibration responses due to the changes in ODS.