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Theses

Dynamique non linéaire des aubages : comportement multi-harmonique avec couplage torsion-flexion

Abstract : In order to cope with growing demand for reducing exhaust gas emissions and increasing flight performance, the aeronautical industry is increasingly moving toward bigger diameter turbojet engine so as to improve dilution rate. The design of these new architectures implies a better control of the vibratory risks. More specifically, the conception of slender fan blades in composite material favors geometrical nonlinear phenomena appearance. Among them, internal resonances or modal interactions occur through modes coupling whose frequencies are commensurate and lead to multi-modes responses that can potentially fasten bladed disks wreck with fatigue. In this context, the objective of this thesis is to improve the internal resonance phenomenon comprehension. On one hand, the aim is to evaluate in design phase the risk of internal resonance appearance. On the other hand, the purpose is to understand the influence of geometrical modifications on the internal resonance behavior. To tackle the problem, several approaches with growing difficulties models are studied. A nonlinear twist and curved beam model with bending torsion coupling is first analyzed. Then, an industrial application representative of a fan blade for future unducted engines architectures is investigated, both experimentally and numerically. For each case, dynamical studies are conducted, based on the harmonic balance method for periodic solution research and coupled with an algorithm to compute and track secondary branches. A parametric analysis for the beam model has shown the strong impact of the nonlinear part of the bending moment, as well as the mode shapes, on the internal resonance appearance. For this model, a study of influence has also revealed the modification of the dynamical behavior when varying the geometry and the damping ratios. The internal resonance has also been observed for the industrial model. It appeared first experimentally when exciting the blade with a vibrating pot. Then it came out numerically through a finite elements model, reduced by the normal form theory. More precisely, it was shown that the used reduction method allows a very good restitution of the dynamical behavior of the blade both with and without nonlinear coupling and with relatively small computational time. Finally, the results obtained for both models can be easily used by engineers during de design phases of future architectures fan blades to evaluate the risk of internal resonances appearance.
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Submitted on : Tuesday, May 24, 2022 - 3:14:13 PM
Last modification on : Tuesday, June 14, 2022 - 11:32:02 AM

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  • HAL Id : tel-03677198, version 1

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Nicolas Di Palma. Dynamique non linéaire des aubages : comportement multi-harmonique avec couplage torsion-flexion. Autre. Université de Lyon, 2022. Français. ⟨NNT : 2022LYSEC001⟩. ⟨tel-03677198⟩

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