Fatigue Strength Assessment Of Centrifugal Compressor Impeller In Aerodynamic Excitation

As energy conversion device widely used in areas such as the energy, transportation and chemicals, the reliability of large centrifugal compressor affects the operational safety directly. Compressor impeller failure investigation results show that the high cycle fatigue caused by excessive dynamic stress is an important form of impeller failure. Among the factors affecting impeller fatigue as material composition, processing, machinery and aerodynamic excitation, impeller forced vibration caused by periodic aerodynamic load is the main cause of impeller high cycle fatigue.This paper studies the centrifugal compressor impeller fatigue strength assessment method under aerodynamic excitation, and provides a reference for impeller fatigue strength design and failure analysis.The integral impeller transient analysis according to the unsteady fluid time domain load is done by using integration method and modal superposition method. According to the comparison results of the two calculation method, the transient analysis methods are evaluated to check impeller dynamic stress under aerodynamic load.The frequency, amplitude and phase of aerodynamic load are obtained from the unsteady calculation results of compressor impeller using Fast Fourier Transform. The aerodynamic excitation phase between adjacent blades is analyzed in detail. For typical load with cyclic symmetric distribution of phase difference between adjacent blades, the interference diagram is used to determine the resonance modal. For non-typical load with non-cyclic symmetric distribution of phase difference, the resonance modal is determined by the result of dynamic stress in all nodal diameters under aerodynamic excitation frequency. Furthermore, the impeller resonance calculation is done under aerodynamic load, and the simplify aerodynamic load calculation method is analysed.Considering the impact of impeller mistuning on impeller resonance, the dynamic stress is corrected and then the fatigue analysis is performed combining impeller dynamic stress with static stress. The result show that the aerodynamic force with non-cyclic symmetry distribution phase exciting zero diameter modal resonance is the main cause of impeller fatigue failure.