FATIGUE ANALYSIS AND LIFETIME ESTIMATION OF CENTRIFUGAL COMPRESSOR IMPELLER BLADES

A multistage centrifugal compressor installed in an air-separation plant was equipped with the inlet guide vanes (IGVs) at the first stage. The impeller blades of the first stage cracked when the compressor just ran about three months. A weakly coupled fluid-structure interaction (FSI) is numerically calculated to analyze the high cycle fatigue (HCF) failure and estimate the lifetime of the impeller blades. In order to obtain the time dependent aerodynamic loads on the impeller blades, three-dimensional unsteady compressible viscous flow in the first whole stage of the centrifugal compressor is simulated. And then, a data interpolation tool is developed to transfer the physical information from fluid meshes to structure meshes, and also, time dependent data is transferred into frequency dependent data using Fast Fourier Transform (FFT). The free vibration mode and forced vibration response of the impeller blades are calculated using finite element method (FEM) and the cyclic symmetry structure of the rotating impeller is modeled by a single segment. According to the numerical result, the HCF lifetime of the impeller blades is estimated using a local stress-strain method. Numerical result shows that the predominated frequency of unsteady aerodynamic loads acting on the impeller blades is equal to the frequency of the IGVs-impeller blades interaction. Both the predicted stress concentration region and lifetime of the impeller blades agree reasonably well with factual fracture case. This study shows that it is feasible to use the weakly coupled FSI simulation to predict the fracture region and lifetime of centrifugal impeller blades.