Blisk components are an integral part of jet engines and power generation systems. Composed of a single monolithic structure, integral blisks combine the blade-and-disk portion of primary components such as the fan, compressor stage, or turbine stage. This design modification increases the aerodynamic performance while decreasing the cost and eliminating time of assembly. However, these benefits come with the loss of blade-disk connection interfaces, which greatly reduces the structure's damping and its ability to attenuate unwanted structural vibrations. Blisk dynamics are impacted by mistuning, which is a disruption of the periodic symmetry of otherwise identical bladed sections. This disruption degrades the overall performance of components. This dissertation advances theoretical and experimental studies into mistuning, both in terms of characterization and vibration localization. A theoretical analysis of wave propagation in periodic structures shows that vibration localization arises from two separate generating mechanisms: an isolated defect or random variations throughout the structure. Through two novel metrics—the band flatness factor and the localization amplification criterion—we establish a unique approach to identifying localized modes on cyclic structures. We present a novel framework that distinguishes between the response of the tuned and mistuned system. A characteristic single-degree-of-freedom response of the tuned system to engine-order forcing forms the basis of our mistuning characterization framework. The actual mistuning (or tuned system) characterization is performed through computations of a modified modal assurance criterion, termed here the modal mistuning criterion. The modal mistuning criterion uses frequency response function data obtained from engine order-forcing profiles and tuned system modes derived from a model to compute the modal contribution to a mistuned response. Finally, this mistuning characterization metric is validated through experimental tests on multiple academic blisk components.
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Kauffman, Jeffrey L.
Doctor of Philosophy (Ph.D.)
College of Engineering and Computer Science
Mechanical and Aerospace Engineering
Length of Campus-only Access
Doctoral Dissertation (Open Access)
Rodriguez, Andres, "Vibrations of Rotationally Periodic Structures: A Metric for Mistuning Characterization and Vibration Localization" (2022). Electronic Theses and Dissertations, 2020-. 1432.