Abstract: The influence on coupling vibrations and stability among
shaft-torsion, disk-transverse and blade-bending of a rotor system with a
mistuned blade's staggle angle was investigated analytically. A
shaft-disk-blade system has been found existing two types of coupling
vibrations, disk-blade (DB), and blade-blade (BB) modes when the shaft was
assumed rigid. If the shaft's torsional flexibility was taken into account, an
additional type of coupling modes, shaft-disk-blade (SDB), appeared. When an
angle-mistuned blade existed, the blades periodicity was destroyed and it was
found to change not only the natural frequencies but also the types of modes.
Due to blade's mistune, the shaft torsion had to participate to balance such
that DB modes vanished and replaced by SDB modes. A mistuned staggle angle was
numerically found to alter the natural frequencies in an almost linear trend.
At last, the rotational effects were found to merge frequency loci and
eventually reached an instability point. Very interestingly, a mistuned blade
diminished the possible instability caused by blade-dominating modes, which
existed in a perfect and periodic rotor. In words, the rotor might benefit from
a mistuned blade from the stability viewpoint. The shaft-dominating mode, yet,
was unaffected by the mistune and retained a possible instability.
