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 viscous damping variations were investigated for an integrally bladed disk, or blisk. Blade response to an inlet total pressure distortion was measured using dynamic strain gauges with the blisk at operating conditions. In addition, a reduced-order analytical model of the blisk was used to predict the blade resonant stress variations. The measured stress variations were found to be strongly ine uenced by unsteady aerodynamic coupling. Bladestructural mistuning and mechanical coupling through hub motion weredetermined to have only a minor ine uence on blade-to-blade stress variations. Stress distribution patterns at resonance and at constant speeds above and below resonance suggested a relationship between stress variations and unsteady aerodynamics. Tosupportthis,aerodynamicdamping variationsmeasured atresonancewereshown to correspond roughly to stress variations. Experimental results were compared to the predicted variations from the reducedorder model. Results from the model indicated that unsteady aerodynamic coupling played an important role in the mistuned response of the blisk.