Early detection of vibration behaviour of aircraft engine multistage axial compressor in pre-surge states during rig testing

Surge is a dangerous aero-elastic phenomenon. When surge occurs a shock wave originates in the gas path of the compressor, which damages individual elements of the compressor, as well as the test beds for measuring the parameters of the workflow. Therefore, early diagnostics of pre-surge states of multistage axial compressors of modern aircraft engines characterized by extremely high aerodynamic loading and small radial clearances between the rotor and the stator is an urgent task. The paper presents the results of the analysis of dynamic processes that take place during throttling of aircraft engine multistage compressors in test bed conditions.  Diagnostic features of the pre-surge state of the compressor were revealed in the signals from strain gauges mounted on the blades, and the signals from sensors of static pressure pulsations installed in the compressor housing. The research was carried out using up-to-date methods of processing and analysis of the signals of dynamic processes based on the fast Fourier transform and wavelet analysis using a 3D representation of the results of the study. The results of the study indicate the possibility of early diagnosis of surge, and also show that several forms of axial vibrations and their respective acoustic frequencies depending on the size of connected masses may occur in the case of loss of gas dynamic stability. The developed methods and means are proposed to be used for the creation of automated systems for preventing surge in compressor rig testing to determine the gas dynamic stability margin.