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Article

Flutter Analysis of the ECL5 Open Fan Testcase Using Harmonic Balance †

1
Institute of Propulsion Technology, German Aerospace Center (DLR), Linder Höhe, 51147 Cologne, Germany
2
Ecole Centrale de Lyon, CNRS, Université Claude Bernard Lyon 1, INSA Lyon, LMFA, UMR 5509, 69130 Ecully, France
*
Author to whom correspondence should be addressed.
This paper is an extended version of our paper published in the Proceedings of the 16th European Turbomachinery Conference (ETC16), Hannover, Germany, 24–28 March 2025, paper no. ETC16-263
Int. J. Turbomach. Propuls. Power 2025, 10(4), 35; https://doi.org/10.3390/ijtpp10040035
Submission received: 20 May 2025 / Revised: 4 August 2025 / Accepted: 6 August 2025 / Published: 2 October 2025

Abstract

This paper presents a flutter analysis of the UHBR Open Fan Testcase ECL5 for an off-design point at part speed and focuses on the second eigenmode, which has a strong torsional character near the blade tip. Recent studies by Pagès et al., using a time-linearized solver, showed strong negative damping for an operating point at 80% speed close to the maximal pressure ratio. This was identified as a phenomenon of convective resonance; for a certain nodal diameter and frequency, the blade vibration is in resonance with convective disturbances that are linearly unstable. In this work, a nonlinear frequency domain method (harmonic balance) is applied to the problem of aerodynamic damping prediction for this off-design operating point. It is shown that, to obtain plausible results, it is necessary to treat the turbulence model as unsteady. The impact of spurious reflections due to numerical boundary conditions is estimated for this case. While strong negative damping is not predicted by the analysis presented here, we observe particularly high sensitivity of the aerodynamic response with respect to turbulence model formulation and the frequency for certain nodal diameters. The combination of nodal diameter and frequency of maximal sensitivities are interpreted as points near resonance. We recover from these near-resonance points convective speeds and compare them to studies of the onset of nonsynchronous vibrations of the ECL5 fan at part-speed conditions.
Keywords: aeroelasticity; CFD, flutter; ECL5; harmonic balance aeroelasticity; CFD, flutter; ECL5; harmonic balance

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MDPI and ACS Style

Frey, C.; Aubert, S.; Ferrand, P.; Fiquet, A.-L. Flutter Analysis of the ECL5 Open Fan Testcase Using Harmonic Balance. Int. J. Turbomach. Propuls. Power 2025, 10, 35. https://doi.org/10.3390/ijtpp10040035

AMA Style

Frey C, Aubert S, Ferrand P, Fiquet A-L. Flutter Analysis of the ECL5 Open Fan Testcase Using Harmonic Balance. International Journal of Turbomachinery, Propulsion and Power. 2025; 10(4):35. https://doi.org/10.3390/ijtpp10040035

Chicago/Turabian Style

Frey, Christian, Stéphane Aubert, Pascal Ferrand, and Anne-Lise Fiquet. 2025. "Flutter Analysis of the ECL5 Open Fan Testcase Using Harmonic Balance" International Journal of Turbomachinery, Propulsion and Power 10, no. 4: 35. https://doi.org/10.3390/ijtpp10040035

APA Style

Frey, C., Aubert, S., Ferrand, P., & Fiquet, A.-L. (2025). Flutter Analysis of the ECL5 Open Fan Testcase Using Harmonic Balance. International Journal of Turbomachinery, Propulsion and Power, 10(4), 35. https://doi.org/10.3390/ijtpp10040035

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