Acoustic blockage effects in unsteady transonic nozzle and cascade flows

Atassi, Hafiz M.; Fang, J.; Ferrand, Pascal

doi:10.2514/6.1995-303

Cited by 4 publications

(3 citation statements)

References 4 publications

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“…In the opposite direction, propagation occurs at neither ND5 nor ND6. Vibration patterns that fulfil this condition of being cut on only in one axial direction are known to be critical for aeroelastic stability [6,33]. The discontinuity observed in the aerodamping curve (Figure 19) for OP-D seems to coincide with the change in the acoustic propagation conditions shown in Figure 18.…”

Section: Acoustic Propagation Conditionsmentioning

confidence: 89%

UHBR Open-Test-Case Fan ECL5/CATANA

Pagès

Duquesne

Aubert

et al. 2022

IJTPP

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The application of composite fans enables disruptive design possibilities but increases sensitivity to multi-physical resonance between aerodynamic, structure dynamic and acoustic phenomena. As a result, aeroelastic problems increasingly set the stability limit. Test cases of representative geometries without industrial restrictions are a key element of an open scientific culture but are currently non-existent in the turbomachinery community. In order to provide a multi-physical validation benchmark representative of near-future UHBR fan concepts, the open-test-case fan stage ECL5 was developed at Ecole Centrale de Lyon. The design intention was to develop a geometry with high efficiency and a wide stability range that can be realized using carbon fibre composites. This publication aims to introduce the final test case, which is currently fabricated and will be experimentally tested. The fan blades are composed of a laminate made of unidirectional carbon fibres and epoxy composite plies. Their structural properties and the ply orientations are presented. To characterize the test case, details are given on the aerodynamic design of the whole stage, structure dynamics of the fan and aeroelastic stability of the fan. These are obtained with a state-of-art industrial design process: static and modal FEM, RANS and LRANS simulations. Aerodynamic analysis focuses on performance and shows critical flow structures such as tip leakage flow, radial flow migration and flow separations. Mechanical modes of the fan are described and discussed in the context of aeroelastic interactions. Their frequency distribution is validated in terms of resonance risk with respect to synchronous vibration. The aeroelastic stability of the fan is evaluated at representative operating points with a systematic approach. Potential instabilities are observed far from the operating line and do not compromise experimental campaigns.

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Section: Acoustic Propagation Conditionsmentioning

confidence: 89%

UHBR Open-Test-Case Fan ECL5/CATANA

Pagès

Duquesne

Aubert

et al. 2022

IJTPP

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“…The acoustic blockage corresponds to backward traveling pressure waves generated downstream of the shock-wave and propagating upstream. When reaching the shock-wave, the velocity of backward traveling pressure waves decreases, which leads to an increase of their amplitude (Atassi et al , 1995). For choke flutter, previous studies have shown the important contribution of the acoustic blockage (Ferrand, 1987; Rendu et al , 2016).…”

Section: Introductionmentioning

confidence: 99%

Choke flutter instability sources tracking with linearized calculations

Duquesne

Rendu

Aubert

et al. 2019

HFF

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Purpose The choke flutter is a fluid-structure interaction that can lead to the failure of fan or compressor blade in turbojet engines. In ultra high bypass ratio (UHBR) fans, the choke flutter appears at part-speed regimes and at low or negative incidence when a strong shock-wave chokes the blade to blade channel. The purpose of this study is to locate the main excitation sources and improving the understanding of the different work exchange mechanisms. This work contributes to avoiding deficient and dangerous fan design. Design/methodology/approach In this paper, an UHBR fan is analyzed using a time-linearized Reynolds-averaged Navier–Stokes equation solver to investigate the choke flutter. The steady-state and the imposed vibration (inter blade phase angle, reduced frequency and mode shape) are selected to be in choke flutter situation. Superposition principle induced by the linearization allow to decompose the blade in numerous small subsections to track the contribution of each local vibration to the global damping. All simulations have been performed on a two-dimensional blade to blade extraction. Findings Result analysis points to a restricted number of excitation sources at the trailing edge which induce a large part of the work exchange in a limited region of the airfoil. Main phenomena suspected are the shock-wave motion and the shock-wave/boundary layer interaction. Originality/value An original excitation source tracking methodology allowed by the linearized calculation is addressed and applied to a UHBR fan test case.

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“…Downstream, acoustic waves propagate at ND4 but neither ND5 nor ND6. Vibration patterns which fulfill this condition of being cut-on only in one axial direction are known to be critical for aeroelastic stability(Atassi et al (1995) andFiquet et al (2020)). Both discontinuities observed in the aerodamping curve (fig.13) for OP-D coincide with changes of the acoustic propagation conditions (ND-1 and ND5) shown in figure12.…”

mentioning

confidence: 99%

UHBR Open-test-case fan ECL5/Catana, Part 2: Mechanical and aeroelastic stability analysis

Pagès,

Duquesne,

Ottavy

et al. 2021

European Conference on Turbomachinery Fluid Dynamics and Thermodynamics

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In Part-1, the ECL5 open-test-case has been introduced. Details on design methodology, geometry, and aerodynamics of the whole stage have been presented. Part-2 focuses herein on structure dynamics and aeroelastic stability. This paper aims to provide the mechanical and aeroelastic stability characteristics of the fan stage obtained with a state-of-art industrial design process. The fan blades are composed of a laminate made of unidirectional carbon fibres and epoxy composite plies. Fibre orientations of each ply are parameters which enable to modify the mechanical behaviour with minimal impact on the aerodynamic performance. Details on the structural properties, the manufacturing process and the ply orientations are presented. First mechanical modes of the fan are described and discussed in the context of aeroelastic interactions. Their frequency distribution is validated in terms of synchronous vibration. Aeroelastic stability of the fan is evaluated at representative operating points with a systematic approach. Potential instabilities are observed far from the operating line. Therefore, they do not compromise experimental campaigns.

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Acoustic blockage effects in unsteady transonic nozzle and cascade flows

Cited by 4 publications

References 4 publications

UHBR Open-Test-Case Fan ECL5/CATANA

UHBR Open-Test-Case Fan ECL5/CATANA

Choke flutter instability sources tracking with linearized calculations

UHBR Open-test-case fan ECL5/Catana, Part 2: Mechanical and aeroelastic stability analysis

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