Computational Models and Damper Concepts for Vibration Reduction of Turbomachinery Blisks

Integrally bladed rotors (IBRs), also known as blisks, are important turbomachinery components at the core of gas turbine engines. In operating conditions, IBRs must withstand large centrifugal forces, high temperatures, and blade vibrations caused by upstream flow perturbations. The combination of the cyclic symmetric design of blisks and their inherent mistuning, i.e. small deviations from the nominal properties and geometry, makes them prone to vibration localization, that can lead to vibration amplification of some of the blades in the system. Unlike traditional bladed disk assemblies, in which blades are connected to the disk portion using frictional joints, blisks are manufactured in one piece. The lack of frictional interfaces in blisks results in lower damping, which in turn causes even larger vibration amplitudes. The concurrent presence of high steady stresses and vibration, combined with the large numbers of cycles that blisks blades must withstand, can lead to blade failure due to high cycle fatigue. As a result, the study and reduction of blisk vibrations is of paramount importance to ensure the safety and reliability of such components. The study of blisk vibration is currently carried out using reduced order models (ROMs), due to the prohibitive computational cost associated with the repeated solution of large size finite element models. Vibration reduction is commonly pursued using ring dampers, which typically present low effectiveness. A two-fold approach is used in this work to tackle the complex problem of vibration characterization and mitigation in IBRs. First, a set of efficient ROM tools is introduced to be used in the design phase. Then, novel damping mechanisms are proposed for vibration reduction in operating conditions. A conditioning technique for projection-based ROMs is presented together with examples of applications. Due to the need to model the effects of repairs (blends) or geometric changes during design iterations, models often require the use of distinct meshes for the same component. A novel method is thus developed to overcome computational issues caused by the use of multiple meshes in ROMs for mistuned blisks. Both methods preserve the accuracy of the ROM and at the same time reduce the overall computational cost. In addition to this, a method is presented to efficiently capture the effects of prestress in geometrically mistuned blisks. Different cases and blend types are examined to prove the generality of the approach, showing excellent agreement with the full order model. The last three chapters are entirely dedicated to novel ring dampers concepts, in which the core idea behind tuned vibration absorbers is leveraged to substantially increase damper effectiveness. This allows for higher levels of energy dissipation by frictional nonlinearities, making it possible for the damper to reduce vibrations even when placed in a region with little blisk-alone motion. First, a preliminary computational study is introduced to prove the validity of the concept. Then, a test rig is presented to experimentally demonstrate the effectiveness of the concept. Finally, a novel damper design is presented and studied using state-of-the-art computational tools.PhDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/155292/1/alupini_1.pd