Fluid Mechanics and Acoustics Laboratory - UMR 5509

LMFA - UMR 5509
Laboratoire de Mécanique des Fluides et d’Acoustique
Lyon
France


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Home > News > Thesis defense

Soutenance de thèse ECL

Leo Girier

Lundi 31 janvier 2022 à 14h00, amphi 203, bât. W1, ECL

Leo Girier

Mode-matching techniques for the modeling of rotor-stator wake-interaction tonal noise, with emphasis on the effects of vane camber

Composition du jury
- Pr. Grace Sheryl, Boston University, Rapporteure
- Pr. Schram Christophe, Von Karman Institute, Rapporteur
- Pr. Auregan Yves, Le Mans Université, Examinateur
- Dr. Ingenito Johanna, Horizon Orientation, Examinatrice
- Pr. Joseph Phillip, University of Southampton, Examinateur
- Pr. Moreau Stéphane, Université de Sherbrooke, Examinateur
- Dr. Posson Hélène, Safran Aircraft Engines, Examinatrice
- Pr. Roger Michel, École Centrale de Lyon, Directeur de thèse
- Dr. Lafitte Anthony, Safran Aicraft Engines, Encadrant

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Résumé

The present work is devoted to the modeling of noise generated by the impingement of fan wakes on outlet guide vanes in turbofan engines, which has been acknowledged as one of the most important source of aircraft noise. Modern fan stages display a high number of blades/vanes, resulting in strong cascade effect. For such configurations, the mode-matching technique chosen in this thesis shown promising capabilities. This is why an extension of this technique to a more realistic vane geometry is proposed, with the addition of camber in two dimensions.

Accounting for camber has a twofold impact on sound propagation though the inter-vane channels: curvature of the center line, and expansion of the cross-section. The latter is introduced by means of a multiple-scale analysis, relying on slow variations along the channel. Then curvature effects are added by restating the wave equation in curvilinear coordinates. The channel expansion plays a significant role on sound transmission and reflection phenomena at all frequencies. It also generates cut-on/cut-off transitions of channel modes, which can drastically change the acoustic behavior. A detailed study of this mechanism has been carried out. On the other hand, it has been observed that curvature only matters above the first cut-off frequency of the channels, for typical outlet guide vane geometries.

Concerning the wakes evolution through the cascade of cambered vanes, only the expansion effect has been modeled. This allowed to recover the wakes slicing and tilting observed in numerical simulations. However, the missing curvature effects proved to be limiting to address noise prediction in realistic configurations. They should be added to ensure reliable results.

Throughout this work, emphasis was also placed on acoustic resonances. Parametric studies have been performed on the influence of vane design parameters and incident perturbation on the prediction of resonant frequencies. The modulation of the resonance pattern by an incident acoustic wave in non-ideal conditions has been explained, as well as the crucial role of cut-on/cut-off transitions at certain frequencies. The influence of acoustic resonances triggered by wake impingement was also studied. It appeared that their occurrence can either reduce or amplify noise.

Agenda

  • Monday 31 January 14:00-16:00 -

    Soutenance de thèse : Leo Girier

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