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Dynamique non-linéaire des systèmes multirotors. Etudes numérique et expérimentale

Abstract : Modern trends in the progress of the machine design are to increase performances while reducing mass. This causes augmented loads in machine parts while the compliances grow as well. The resulting dynamical response occur at accrued levels, putting forward the non-linear phenomena. The aim of this thesis is to study non-linear structural dynamics, especially in view of application to multi-shaft aircraft engines rotordynamics. This problematics is investigated by theory and experiment. As for the theoretical development, we address the dynamical response of strongly non-linear systems under multi-frequency excitations. To this aim, the models of roller bearings are studied and implemented from the point of view of application to rotordynamics computations. In particular, these models take radial clearance and non-linear contact stiffness into account. In order to deal with multiple unbalance excitations which are present in multi-shaft rotor systems, we have elaborated a generalized harmonic balance approach so as to predict the resulting quasi-periodic motions. This work has been applied to a dual shaft test rig with an intershaft bearing built during this study. Methods of stability evaluation are also considered in view of extensions to quasi-periodic motions. In the experimental part of the work, we have designed and studied a dual shaft test rig with an intershaft bearing. The overall modal analysis of this rig matches a real aircraft engine's rotordynamical behavior. After the design and construction of the rig, several operational configurations have been tested. Firstly, we have studied the unbalance response of the machine under the nominal co-rotating conditions in order to validate the design approach and estimate the residual unbalance of the machine. Secondly, the counter-rotating operation has been tested. Finally, an additional mass has been mounted on one of the shafts. This has allowed to lower one of the modes into the operational range of the machine. The overall test results have enabled the observations of dynamical phenomena typical for the dual shaft dynamics both from the rotordynamical and non-linear points of view : forward and backward whirls, quasi-periodic precession motion, resonance peaks distortion and superharmonic response.
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Submitted on : Thursday, December 3, 2009 - 2:17:40 PM
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Mikhail Guskov. Dynamique non-linéaire des systèmes multirotors. Etudes numérique et expérimentale. Mécanique [physics.med-ph]. Ecole Centrale de Lyon, 2007. Français. ⟨tel-00438353⟩

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