Small Random Aerodynamic Mistuning and Its Effect on Compressor Rotor Forced Response

Small blade-to-blade geometric differences in compressor rotors are always present due to manufacturing tolerances, operational wear, etc. The small blade geometric variations affect both the structural response and aerodynamic response of the rotor, known as structural mistuning and aerodynamic mistuning, respectively. Extensive structural mistuning research has shown that small blade geometric variations can be effectively modeled by blade frequency deviations, which are the basis of the structural mistuning matrix in various reduced-order models. Aerodynamically, small blade geometric variations result in blade unsteady loading and aerodynamic coupling variations. A semi-analytical flat-plate cascade model was developed in this paper to quantify the aerodynamic mistuning matrix with random blade spacing variation. Monte Carlo simulations based on a three-stage axial research compressor were conducted to study the effect of small random blade spacing variation on blade forced response. Due to the high mass ratio, the effect of structural mistuning is much stronger than the effect of aerodynamic mistuning, and thus it dominates the rotor resonant frequencies. On the other hand, since aerodynamic damping is the primary damping source in a blisk-type rotor, aerodynamic mistuning alters the rotor blade resonant amplitudes by altering the aerodynamic damping. Blade spacing variations lead to blade-to-blade external forcing function variations, which also play an important role in altering the blade forced response curve.