Analysis of a Turbine Bladed Disk With Structural and Aerodynamic Mistuning - Archive ouverte HAL Accéder directement au contenu
Communication Dans Un Congrès Année : 2017

Analysis of a Turbine Bladed Disk With Structural and Aerodynamic Mistuning

Résumé

In this paper the effects of mistuning on the flutter stability of a turbine blade are analysed. Two types of mistuning are considered, frequency mistuning and aerodynamic mistun-ing. The study concentrates on the the first family of modes (1F, first flap) as the blade fluttered in this mode during test. For the frequency mistuning analysis, the 1F frequency is varied around the annulus but the 1F mode shapes remain the same for all the blades. The mistuning analyses are performed by using a reduced order model (ROM) based on an eigen-value analysis of the linearized modal aeroelastic system with the aerodynamic matrix calculated from the aerodynamic influence coefficients. The influence coefficients required for this algorithm are obtained from a three-dimensional, non-linear aeroelastic solver (AU3D) by shaking one blade in the datum (tuned) frequency and mode and recording aerodynamic forces on the other blades in the assembly. After the ROM is validated against the non-linear method for the tuned case, it is used for the mistuning and mis-staggering study as time-domain computations of such cases are very time consuming. The results of this paper indicate that, frequency mistuning is always stabilizing but aerodynamic mistuning can be destabilizing under certain conditions. Moreover, it is shown that the effect of frequency mistuning is much higher than the one of aerodynamic asymmetries and that structural coupling limits the effects of mistuning. NOMENCLATURE IBPA Interblade phase angle ND Nodal diameter FMM Fundamental Mistuning Model AIC Aerodynamic influence coefficient ∆ω Mistuning amplitude Λ 0 Tuned stiffness matrix Π Pressure ratio ζ aero Aerodynamic damping σ Standard deviation ω * Reduced frequency, ω * = ω 0 c/V ω 0 s Tuned blade frequency of the s th blade ω s Mistuned blade frequency of the s th blade ω Complex system frequency A m0 Tuned aerodynamic influence coefficient matrix A m0 x Tuned aerodynamic influence coefficient matrix in physical space A m x Aerodynamic matrix containing tuned and mistuned forces in physical spacê A m Mistuned aerodynamic matrix A Frequency mistuned matrix E Discrete Fourier transformation matrix E * Hermitian of the discrete Fourier transformation matrix I Identity matrix (tuned mass matrix) F Modal force N Blade number a 0 s Tuned aerodynamic influence coefficient on the s th blade f 0 ba Tuned blade alone frequency q Travelling wave displacement 1 INTRODUCTION Structural or aerodynamic mistuning, i.e. deviations from the design intent, in turbomachinery bladed disks and blisks are caused by manufacturing tolerances and/or wear. It has been long known that they affect the flutter stability of bladed assemblies (see, for example, [1, 2]). In fact, intentional mis-tuning has been used to successfully suppress flutter in both compressor and turbine rotors [3, 4]. The vast majority of mistuning studies have focused on structural mistuning and been neglecting any aerodynamic coupling between blades. High fidelity studies incorporating both structural and aerodynamic coupling and mistuning effects have been comparatively rare [5]. Recently, Kielb et al. [5, 6] investigated the effects of frequency and aerodynamic mistun-ing on the flutter stability of a front-stage compressor blisk. The results indicated that, frequency mistuning and certain patterns of aerodynamic asymmetry were able to suppress flutter but that random aerodynamic asymmetries destabilized the blades. This paper uses the same approach to study the effect of mistuning on the flutter stability of a low pressure turbine rotor. The bladed-disk rotor was designed by ITP and tested by CTA as part of the European Collaborative project FUTURE [4, 7] and is representative of a state-of-the-art low pressure turbine. Two types of mistuning, frequency mistuning and aerodynamic mistuning, are chosen for this study. They are analyzed using a mistuning model similar to the one developed by Kielb et al. [5]. The model is based on an eigenvalue analysis of the linearized modal aeroelastic system. It combines a reduced order structural coupling model with an aerodynamic coupling model based on aerodynamic influence coefficients (AIC) obtained from unsteady computational fluid dynamic (CFD) simulations. Previous work by the authors [8] has shown that this method predicts similar flutter boundaries for a fan blade as a non-linear CFD analysis. Aerodynamic mistuning is mod-eled by introducing an aerodynamic asymmetry (such as would arise from circumferential stagger angle variations, for example) in the aerodynamic coupling model. For simplicity, the term reduced order model (ROM) will be used to refer to the model based on Fundamental Mistuning Model with Aerodynamic Influence Coefficients. The work is divided into three parts. First, the flutter stability of the tuned assembly in the first flap (1F) mode is investigated. Three-dimensional, non-linear URANS simulations are used to determine the influence of loading on the aeroelastic stability of the rotor blade. The results are also used to validate the ROM for the tuned system. In the second part, the ROM is used to study the effects of frequency mistuning on aero-damping. Finally, the sensitivity of the system to aerodynamic asymmetries is studied while frequency mistuning is set to zero.
Fichier principal
Vignette du fichier
franz2017.pdf (838.49 Ko) Télécharger le fichier
Origine : Fichiers produits par l'(les) auteur(s)
Loading...

Dates et versions

hal-02544648 , version 1 (16-04-2020)

Identifiants

Citer

Dimitri Franz, Loic Salles, Sina Stapelfeldt. Analysis of a Turbine Bladed Disk With Structural and Aerodynamic Mistuning. ASME Turbo Expo 2017: Turbomachinery Technical Conference and Exposition, Jun 2017, Charlotte, United States. ⟨10.1115/GT2017-64586⟩. ⟨hal-02544648⟩
125 Consultations
201 Téléchargements

Altmetric

Partager

Gmail Facebook X LinkedIn More