title: MAX Modeling of Integrally Bladed Rotors with Blends, Mistuning, and Prestress
Creators: name: LUPINI, Andrea
name: EPUREANU, Bogdan I.
Publisher: name: Proceedings of the 8th European Conference for Aeronautics and Space Sciences. Madrid, Spain, 1-4 july 2019
Year: 2019
Subjects: STRUCTURES
TURBOMACHINES
SIMULATION

description: Integrally bladed rotors (IBRs) are critical components of turbomachinery in the aerospace industry. The use of IBRs has been increasing recently because they provide enhanced performance and reduced weight. One of the most significant challenges posed by IBRs is their low level of damping. The low damping leads to unwanted vibrations that increase the risk of high-cycle fatigue. In addition, IBRs are typically mistuned in real applications, i.e. they present deviations from the nominal geometry due to manufacturing tolerances, damages or wear even though they are designed to be nominally cyclic structures. Mistuning can lead to vibration localization, which further increases the risk of high cycle fatigue. Thus, the geometric design of IBRs is very important. In addition, foreign object damage can affect IBR blades during operation. Distinct from bladed disks with inserted blades, IBRs cannot have their blades replaced because IBRs are manufactured in one piece. As a result, other repair strategies must be used. IBR blades can be repaired by blending, i.e. by removing material in the damaged region to modify the local geometry as to create a smooth surface able to lower stress concentrations while also preserving satisfactory aerodynamic, structural, and vibration characteristics. Such repairs introduce large mistuning in IBRs, which can increase vibration levels. For this reason, it is necessary to optimize blend shapes and locations and to assess their impact on IBR structural dynamics. Finite element (FE) models are traditionally used to study the structural dynamics of IBRs. It is common for industrial models to have several millions of degrees of freedom per sector, making it challenging to obtain results in a timely fashion. Furthermore, the stochastic nature of mistuning requires the use of Monte Carlo simulations to evaluate the expected vibration amplitudes. For this reason, reduced-order models have been used in lieu of FE models to reduce the computational cost of such analyses. A Mode-Accelerated X-Xr (MAX) method was proposed by the authors to study the effects of such blends. In this work, enhancements to the MAX method are presented to accommodate the combined presence of blends and that of other effects, such as blade frequency mistuning and prestress due to centrifugal forces. The use of multiple FE meshes in a single model is also addressed, making it possible to accommodate the use of morphed meshes to better capture the geometry of blended sectors. This enhanced MAX method, referred to as MAX+, is presented. MAX+ is validated by comparing its predictions to high-fidelity FE models, and it is shown to be efficient and effective for simulating blended IBRs in both bench and rotating conditions. Furthermore, the MAX+ approach can be used for the optimization of blend shapes, locations, and patterns when multiple blends are present.