Validation of a Modal Work Approach for Forced Response Analysis of Bladed Disks

Lorenzo Pinelli,Francesco Lori,Roberto Pacciani,Michele Marconcini,Andrea Arnone

doi:10.3390/app11125437

Lorenzo Pinelli, Francesco Lori + Show 3 more

Open Access

https://doi.org/10.3390/app11125437

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Journal: Applied sciences	Publication Date: Jun 11, 2021
Citations: 7	License type: CC BY 4.0

Affiliation: University of Florence

Abstract

The paper describes a numerical method based on a modal work approach to evaluate the forced response of bladed disks and its validation against numerical results obtained by a commercial FEM code. Forcing functions caused by rotor–stator interactions are extracted from CFD unsteady solutions properly decomposed in time and space to separate the spinning perturbation acting on the bladed disk in a cyclic environment. The method was firstly applied on a dummy test case with cyclic symmetry where the forcing function distributions were arbitrarily selected: comparisons for resonance and out of resonance conditions revealed an excellent agreement between the two numerical methods. Finally, the validation was extended to a more realistic test case representative of a low-pressure turbine bladed rotor subjected to the wakes of two upstream rows: an IGV with low blade count and a stator row. The results show a good agreement and suggest computing the forced response problem on the finer CFD blade surface grid to achieve a better accuracy. The successful validation of the method, closely linked to the CFD environment, creates the opportunity to include the tool in an integrated multi-objective procedure able to account for aeromechanical aspects.

Highlights

Bladed-disk vibration has been studied by researchers and designers for more than half a century given the risks posed to turbomachineries, such as aeronautical engines and gas and steam turbines for energy production [1,2]
The two methods for the forced response analysis of a bladed disk are presented: the implemented tool based on the modal work, and the method available in the ANSYS suite used for validation purposes
For the dummy test case, various arbitrary rotating forcings were imposed to different mode shape families reproducing resonance crossings, whereas when studying the forced response of the bladed rotor, the forcing functions were directly extracted from an unsteady multi-row simulation

Summary

Introduction

Bladed-disk vibration has been studied by researchers and designers for more than half a century given the risks posed to turbomachineries, such as aeronautical engines and gas and steam turbines for energy production [1,2]. Vibration issues can jeopardize the reliable design of these components, leading, in the worst cases, to catastrophic HCF failures In this context, an accurate aeromechanical design able to prevent vibration risk is required to avoid or reduce the vibration amplitudes of components mainly due to forced response or flutter phenomena [3]. Thanks to the increase of computing resources, more accurate computational methods for aeromechanical study have been applied to a wider part of turbomachinery modules Such methods are implemented, for instance, to assess the flutter occurrence [4,5] and the effect of mistuning and interlocking on the fluid-structure instability conditions [6,7] or to compute the aerodynamic forcing that can excite the blade row in regards to the resonance condition in order to evaluate maximum displacements and stresses [8,9,10,11]. There is a vast literature that addresses the latter phenomenon proposing numerical methodologies [12,13]

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