International audienceCe travail traite de la problématique des instabilités aéroélastiques, obse... more International audienceCe travail traite de la problématique des instabilités aéroélastiques, observées au niveau des joints labyrinthes de turbopompes. Ces instabilités peuvent mener à la rupture prématurée du joint et/ou des éléments de structure environnants. L'intégration d'un modèle flexible de stator a pour vocation d'apporter une nouvelle interprétation des phénomènes d'instabilités observés au voisinage de ces joints
Increasing the efficiency of turbomachines is a major concern as it directly translates into lowe... more Increasing the efficiency of turbomachines is a major concern as it directly translates into lower environmental impact and improved operational costs. One solution is to reduce the blade-casing operating clearance in order to mitigate aerodynamic losses at the unavoidable cost of increased structural unilateral contact and friction occurrences. In centrifugal compressors, the dynamic behaviour of the structures interacting through unilateral contact and friction is not yet fully understood. In fact, the heat generated during such events may affect the dynamics through thermal stresses. This paper presents a complete thermomechanical modelling strategy of impeller rotor and casing, and of blade-tip/casing contact events. A fully coupled thermomechanical modal synthesis technique is introduced and applied to turbomachinery-related models. The blisk is reduced via a hybrid modal synthesis technique combining the Craig-Bampton method and the characteristic constraint mode method. The c...
Advanced rotating machinery, using small rotors or working at high rotating speeds, require a com... more Advanced rotating machinery, using small rotors or working at high rotating speeds, require a complete control of the vibration components. Lubrication systems, such as hydrodynamic journal bearings play a crucial role in the dynamical behavior of the whole machinery and have a significant influence on structure vibrations. Fluid Structure Interaction (FSI) between the lubricant and the rotating shaft has to be taken into account. Predictions of the shaft vibrations are difficult because of the nonlinear behavior of the hydrodynamic bearing. Besides, recent improvements in surface texturing have shown several enhancements in hydrodynamic lubrication. However, effects of the texture pattern on the dynamic behavior of the system are not well known and need to be properly analyzed. In this work, we present the results of a monolithic algorithm solving the non-linear coupling problem of a rotating shaft on two hydrodynamic bearings. First, homogenization techniques of Reynolds equation ...
The aim of this study is to analyse the influence of surface texturing on the dynamic behavior of... more The aim of this study is to analyse the influence of surface texturing on the dynamic behavior of a shaft on two hydrodynamic bearings. A prediction algorithm is presented with Fluid Structure Interaction (FSI) between the rotating shaft and the lubricant based on finite element method. Cavitation in bearings is taken into account. The hydrodynamic flow in the texturing pattern is modeled by two multi-scale algorithms. Static, modal and transient analyses are performed in order to predict the impact of several texturing patterns on the system vibrations.
Reducing the clearance between blade tips and casing is an important factor in increasing the per... more Reducing the clearance between blade tips and casing is an important factor in increasing the performance of turbomachines such as turbofan engines. However, small clearances lead to more chances of rotor-stator contact, which can cause unstable vibrations. To improve the prediction of such contact-related phenomena, this paper proposes a model that includes potential contacts between the fan blade tips and their surrounding casing. This phenomenological model consists of a fully flexible bladed rotor and a flexible casing. The bladed rotor model is built according to the method developed by Lesaffre (1) and based on the approximations used by Sinha (2). The casing model is composed of an elastic ring with isotropic suspension. Two different contact formulations have been developed: a 3D contact detection law, which incorporates 3D model kinematics along with 3D local geometry of the contact area, is compared to a simpler formulation. For both formulations, once the clearance has be...
Des joints labyrinthes sont utilisés dans les turbopompes spatiales pour limiter les fuites du ga... more Des joints labyrinthes sont utilisés dans les turbopompes spatiales pour limiter les fuites du gaz qui entraine la turbine dans l’interstice séparant le rotor du stator. Les tendances actuelles sont à la minimisation des jeux (pour optimiser le rendement) et à l’allègement du stator. Ces évolutions rendent nécessaires l’élaboration de modèles plus prédictifs au niveau de la prise en compte des fuites et de la souplesse du stator. L’objet de ce travail est d’étudier l’influence de la modélisation des efforts de cisaillement, générés par le fluide aux parois, sur la stabilité d’un système composé d’un arbre indéformable qui ne tourne pas et d’un stator qui admet une flexibilité orthoradiale. Ce système s’inscrit dans un contexte de couplage fort entre le fluide et la structure.
This article focuses on the stability study of a rotor/stator interaction via a labyrinth seal. T... more This article focuses on the stability study of a rotor/stator interaction via a labyrinth seal. To predict the destabilizing force exerted by the labyrinth seal, a single-control volume analysis is performed. The main contribution is a new model of the air flow in the control volume of labyrinth seal with temperature as a parameter and a new bladed disk model for study of the coupling phenomenon in the rotor/stator systems.
Abstract: This paper deals with fluid-structure interactions (FSI), involving a blade profile. An... more Abstract: This paper deals with fluid-structure interactions (FSI), involving a blade profile. An external excitation at a fixed frequency is applied to the structure, and the effect of the fluid on the damping is studied by analyzing Frequency Forced Response (FFR). In order to predict the dynamic behavior of such system, a fully coupled numerical methodology is developed. On the one hand, to compute the time periodic aerodynamic field, a numerical approach the Time Spectral Method (TSM [Sicot (2009)]) or an analytical model (theory of Theodoresen [Theodorsen (1935)]) is used. On the other hand, the Harmonic Balance Method (HBM [Grolet and Thouverez (2012)]) allows the computation of the periodic response for the nonlinear mechanical structure under external/fluid loading. These two spectral approaches will be coupled in order to reach directly the periodic steady state solution.
Volume 6C: 18th Biennial Conference on Mechanical Vibration and Noise, 2001
This paper presents a research devoted to the study of instability phenomena in non-linear model ... more This paper presents a research devoted to the study of instability phenomena in non-linear model with a constant brake friction coefficient. The condition of stability is based on the resolution of a generalized eigenvalue problem and the limit cycle amplitude are determined by the center manifold reduction. A model is presented for the analysis of whirl mode vibration in aircraft braking systems. In this study, a non-linear material behaviour of the brake heat stack is considered. This non-linearity is expressed as a polynomial. The model does not require the use of brake negative damping and predicts that instability can occur with a constant brake friction coefficient. The center manifold approach is used to obtain equations for the limit cycle amplitude. The brake friction coefficient is used as unfolding parameter of the fundamental Hopf bifurcation point. The analysis shows that stable and unstable limit cycles can exist for a given constant brake friction coefficient.
Rotor systems have wide applications in industries, including aero engines, turbo generators, and... more Rotor systems have wide applications in industries, including aero engines, turbo generators, and gas turbines. Critical behaviors promoted by the system unbalance and the contact between rotor and stator lead to important nonlinearities on system dynamics. This paper investigates the complex behavior presented by a rotor-stator system’s dynamics due to intermittent contact. A four-degree-of-freedom Jeffcott nonsmooth rotor/stator system is used to describe the rotor behavior, while a viscoelastic suspended rigid cylinder represents the stator. Numerical simulations are carried out showing rich dynamics that include periodic, quasiperiodic, and chaotic responses. Special attention is dedicated to chaotic behavior and the calculation of Lyapunov exponents is employed as a diagnostic tool.
In order to increase the aerodynamic performances of their engines, aircraft engine manufacturers... more In order to increase the aerodynamic performances of their engines, aircraft engine manufacturers try to minimize the clearance between rotating and stationary parts in axial and centrifugal compressors. Consequently, the probability of contact increases, leading to undesirable phenomena caused by forced excitation of the natural modes, or by modal interaction. Due to the complexity of these phenomena, many numerical studies have been conducted to gain a better understanding of the physics associated with them, looking primarily at their respective influence on potential unstable behaviors. However, the influence of other physical phenomena, such as friction and wear, remains poorly understood. The aim of this work is to show some effects associated with friction and wear on the dynamic behavior resulting from blade-to-casing interaction. The numerical study reported here is based on a simplified finite element model of a rotating bladed disk and a flexible casing. The contact algor...
International audienceCe travail traite de la problématique des instabilités aéroélastiques, obse... more International audienceCe travail traite de la problématique des instabilités aéroélastiques, observées au niveau des joints labyrinthes de turbopompes. Ces instabilités peuvent mener à la rupture prématurée du joint et/ou des éléments de structure environnants. L'intégration d'un modèle flexible de stator a pour vocation d'apporter une nouvelle interprétation des phénomènes d'instabilités observés au voisinage de ces joints
Increasing the efficiency of turbomachines is a major concern as it directly translates into lowe... more Increasing the efficiency of turbomachines is a major concern as it directly translates into lower environmental impact and improved operational costs. One solution is to reduce the blade-casing operating clearance in order to mitigate aerodynamic losses at the unavoidable cost of increased structural unilateral contact and friction occurrences. In centrifugal compressors, the dynamic behaviour of the structures interacting through unilateral contact and friction is not yet fully understood. In fact, the heat generated during such events may affect the dynamics through thermal stresses. This paper presents a complete thermomechanical modelling strategy of impeller rotor and casing, and of blade-tip/casing contact events. A fully coupled thermomechanical modal synthesis technique is introduced and applied to turbomachinery-related models. The blisk is reduced via a hybrid modal synthesis technique combining the Craig-Bampton method and the characteristic constraint mode method. The c...
Advanced rotating machinery, using small rotors or working at high rotating speeds, require a com... more Advanced rotating machinery, using small rotors or working at high rotating speeds, require a complete control of the vibration components. Lubrication systems, such as hydrodynamic journal bearings play a crucial role in the dynamical behavior of the whole machinery and have a significant influence on structure vibrations. Fluid Structure Interaction (FSI) between the lubricant and the rotating shaft has to be taken into account. Predictions of the shaft vibrations are difficult because of the nonlinear behavior of the hydrodynamic bearing. Besides, recent improvements in surface texturing have shown several enhancements in hydrodynamic lubrication. However, effects of the texture pattern on the dynamic behavior of the system are not well known and need to be properly analyzed. In this work, we present the results of a monolithic algorithm solving the non-linear coupling problem of a rotating shaft on two hydrodynamic bearings. First, homogenization techniques of Reynolds equation ...
The aim of this study is to analyse the influence of surface texturing on the dynamic behavior of... more The aim of this study is to analyse the influence of surface texturing on the dynamic behavior of a shaft on two hydrodynamic bearings. A prediction algorithm is presented with Fluid Structure Interaction (FSI) between the rotating shaft and the lubricant based on finite element method. Cavitation in bearings is taken into account. The hydrodynamic flow in the texturing pattern is modeled by two multi-scale algorithms. Static, modal and transient analyses are performed in order to predict the impact of several texturing patterns on the system vibrations.
Reducing the clearance between blade tips and casing is an important factor in increasing the per... more Reducing the clearance between blade tips and casing is an important factor in increasing the performance of turbomachines such as turbofan engines. However, small clearances lead to more chances of rotor-stator contact, which can cause unstable vibrations. To improve the prediction of such contact-related phenomena, this paper proposes a model that includes potential contacts between the fan blade tips and their surrounding casing. This phenomenological model consists of a fully flexible bladed rotor and a flexible casing. The bladed rotor model is built according to the method developed by Lesaffre (1) and based on the approximations used by Sinha (2). The casing model is composed of an elastic ring with isotropic suspension. Two different contact formulations have been developed: a 3D contact detection law, which incorporates 3D model kinematics along with 3D local geometry of the contact area, is compared to a simpler formulation. For both formulations, once the clearance has be...
Des joints labyrinthes sont utilisés dans les turbopompes spatiales pour limiter les fuites du ga... more Des joints labyrinthes sont utilisés dans les turbopompes spatiales pour limiter les fuites du gaz qui entraine la turbine dans l’interstice séparant le rotor du stator. Les tendances actuelles sont à la minimisation des jeux (pour optimiser le rendement) et à l’allègement du stator. Ces évolutions rendent nécessaires l’élaboration de modèles plus prédictifs au niveau de la prise en compte des fuites et de la souplesse du stator. L’objet de ce travail est d’étudier l’influence de la modélisation des efforts de cisaillement, générés par le fluide aux parois, sur la stabilité d’un système composé d’un arbre indéformable qui ne tourne pas et d’un stator qui admet une flexibilité orthoradiale. Ce système s’inscrit dans un contexte de couplage fort entre le fluide et la structure.
This article focuses on the stability study of a rotor/stator interaction via a labyrinth seal. T... more This article focuses on the stability study of a rotor/stator interaction via a labyrinth seal. To predict the destabilizing force exerted by the labyrinth seal, a single-control volume analysis is performed. The main contribution is a new model of the air flow in the control volume of labyrinth seal with temperature as a parameter and a new bladed disk model for study of the coupling phenomenon in the rotor/stator systems.
Abstract: This paper deals with fluid-structure interactions (FSI), involving a blade profile. An... more Abstract: This paper deals with fluid-structure interactions (FSI), involving a blade profile. An external excitation at a fixed frequency is applied to the structure, and the effect of the fluid on the damping is studied by analyzing Frequency Forced Response (FFR). In order to predict the dynamic behavior of such system, a fully coupled numerical methodology is developed. On the one hand, to compute the time periodic aerodynamic field, a numerical approach the Time Spectral Method (TSM [Sicot (2009)]) or an analytical model (theory of Theodoresen [Theodorsen (1935)]) is used. On the other hand, the Harmonic Balance Method (HBM [Grolet and Thouverez (2012)]) allows the computation of the periodic response for the nonlinear mechanical structure under external/fluid loading. These two spectral approaches will be coupled in order to reach directly the periodic steady state solution.
Volume 6C: 18th Biennial Conference on Mechanical Vibration and Noise, 2001
This paper presents a research devoted to the study of instability phenomena in non-linear model ... more This paper presents a research devoted to the study of instability phenomena in non-linear model with a constant brake friction coefficient. The condition of stability is based on the resolution of a generalized eigenvalue problem and the limit cycle amplitude are determined by the center manifold reduction. A model is presented for the analysis of whirl mode vibration in aircraft braking systems. In this study, a non-linear material behaviour of the brake heat stack is considered. This non-linearity is expressed as a polynomial. The model does not require the use of brake negative damping and predicts that instability can occur with a constant brake friction coefficient. The center manifold approach is used to obtain equations for the limit cycle amplitude. The brake friction coefficient is used as unfolding parameter of the fundamental Hopf bifurcation point. The analysis shows that stable and unstable limit cycles can exist for a given constant brake friction coefficient.
Rotor systems have wide applications in industries, including aero engines, turbo generators, and... more Rotor systems have wide applications in industries, including aero engines, turbo generators, and gas turbines. Critical behaviors promoted by the system unbalance and the contact between rotor and stator lead to important nonlinearities on system dynamics. This paper investigates the complex behavior presented by a rotor-stator system’s dynamics due to intermittent contact. A four-degree-of-freedom Jeffcott nonsmooth rotor/stator system is used to describe the rotor behavior, while a viscoelastic suspended rigid cylinder represents the stator. Numerical simulations are carried out showing rich dynamics that include periodic, quasiperiodic, and chaotic responses. Special attention is dedicated to chaotic behavior and the calculation of Lyapunov exponents is employed as a diagnostic tool.
In order to increase the aerodynamic performances of their engines, aircraft engine manufacturers... more In order to increase the aerodynamic performances of their engines, aircraft engine manufacturers try to minimize the clearance between rotating and stationary parts in axial and centrifugal compressors. Consequently, the probability of contact increases, leading to undesirable phenomena caused by forced excitation of the natural modes, or by modal interaction. Due to the complexity of these phenomena, many numerical studies have been conducted to gain a better understanding of the physics associated with them, looking primarily at their respective influence on potential unstable behaviors. However, the influence of other physical phenomena, such as friction and wear, remains poorly understood. The aim of this work is to show some effects associated with friction and wear on the dynamic behavior resulting from blade-to-casing interaction. The numerical study reported here is based on a simplified finite element model of a rotating bladed disk and a flexible casing. The contact algor...
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Papers by Fabrice Thouverez