Aerodynamic effects on blade vibratory stress variations

Blade-to-blade variations in blade resonant frequencies, known as mistuning , and how these variations are related to vibratory stress amplitude and vi scous damping variations were investigated for an integrally bladed disk, o r blisk. Blade response to an inlet total pressure distortion was measured using dynamic strain gauges with the blisk at operating conditions. In addi tion, a reduced-order analytical model of the blisk was used to predict the blade resonant stress variations. The measured stress variations were foun d to be strongly influenced by unsteady aerodynamic coupling. Blade structu ral mistuning and mechanical coupling through hub motion were determined to have only a minor influence on blade-to-blade stress variations. Stress di stribution patterns at resonance and at constant speeds above and below res onance suggested a relationship between stress variations and unsteady aero dynamics. To support this, aerodynamic damping variations measured at reson ance were shown to correspond roughly to stress variations. Experimental re sults were compared to the predicted variations from the reduced-order mode l. Results from the model indicated that unsteady aerodynamic coupling play ed an important role in the mistuned response of the blisk.