The influence on coupling vibration of a rotor system due to a mistuned blade length

The influence on coupling vibrations among shaft-torsion, disk-transverse and blade-bending of a rotor system with a mistuned blade length was investigated analytically. The shaft–disk–blades system appeared to have four types of coupling vibrations, shaft–blade (SB), shaft-disk-blade (SDB), disk–blade (DB), and blade–blade (BB) mode. The natural frequencies in a mistuned blade were not only found changed but also the types of coupling modes. First, the DB modes in a tuned system disappeared and instead they are replaced by SDB modes. Second, the disk experienced mode localization due to the mistuned blade. The results also showed that every mode's frequency varied with the mistuned error linearly in one direction, either positive or negative, but not in both directions. At last, the effects of rotation on the changes of the rotor's natural frequencies were illustrated. Frequency loci showed merging phenomenon with an increase in the rotational speed.