Effects of multiple cracks on the forced response of centrifugal impellers

• A hybrid interface CMS method is developed for impellers with multiple cracks.
• Shifts of natural frequencies due to double cracks are parametrically investigated.
• The effects of double cracks on the forced response of impellers are presented.
• Vibration localization among blades in impellers with double cracks is investigated.

The effects of multiple cracks on the forced response of centrifugal impellers are investigated using a finite-element based component mode synthesis method (CMS) in this paper. The main objective is to gain some insights into the response characteristics of multiple cracked impellers and to explore efficient methods for identifying the cracks. First, in order to generate an efficient model for the nonlinear vibration analysis, a novel hybrid interface CMS method is proposed and used to conduct reduced-order modeling for the cracked impeller. Then, a method for multiple cracks modeling is developed to account for the crack breathing effects. Finally, numerical results are presented using a representative impeller with double cracks. The shifts of natural frequencies and the nonlinear forced response due to multiple cracks are of interest. Lengths and relative positions of the cracks are also considered. The results show that the natural frequencies and forced response become complexly depending on the lengths and relative positions of cracks, and the response amplitudes of blades periodically fluctuate versus blade number when an impeller suffers from cracks or mistuning. A potential method for identifying the lengths and relative positions of multiple cracks are also discussed in this paper.