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See detailModélisation des tensions circonférentielles en simulation méridienne d'écoulements en turbomachines
Thomas, Jean-Philippe ULg

Doctoral thesis (2012)

The systematic use of three-dimensional Navier-Stokes simulations being too demanding in turbomachinery design phase, throughflow simulation, two-dimensional, simpler and faster, is used extensively on an ... [more ▼]

The systematic use of three-dimensional Navier-Stokes simulations being too demanding in turbomachinery design phase, throughflow simulation, two-dimensional, simpler and faster, is used extensively on an industrial scale. However, its limitation is its need for empirical information to reproduce the action of the blades and the effect of three-dimensional components of the flow, higher-order elements compared to the classical throughflow. We propose to lead to a decrease of empiricism needed by the classical throughflow by obtaining this information autonomously. Obtaining information of a circumferential order may be considered in resolving all the components of the flow with a purely three-dimensional code or by accommodating an approximate solution with a reduced numerical cost, the way chosen in this contribution. To do this, we propose to extend to the circumferential case the He's "nonlinear harmonic method", of proved efficiency in the case of approximate reproduction of unsteadiness. Adapting this technique to the throughflow model passes through a reformulation of the presence of blades. Indeed, the use of Fourier series requires a continuous circumferential evolution of flow, prohibiting the existence of local impermeability condition. To work around this feature of the circumferential case, the effect of the blades is modeled by a force field sufficiently continuous and formalized by the Peskin's "immersed boundary method". The validation of the new technique, resulting from an innovative combination of the harmonic and immersed boundary methods inside a throughflow code, is performed on the case of inviscid flow around a cylinder. It illustrates the capabilities of the harmonic throughflow to access higher order information, that enrich the mean flow but also make available the circumferential view of the flow from the Fourier modes resolved. Finally, the harmonic throughflow is applied to a stator airfoil and a single-stage compressor. It is shown that after adjusting the model to the specific geometry of thin profiles, it is possible to access information of higher order. In particular, the model captures the potential characteristics of circumferential non-uniformities on the entire vein and the viscous characteristics near meridional walls. [less ▲]

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See detailToward a High Order Throughflow - Investigation of the Nonlinear Harmonic Method Coupled With an Immersed Boundary Method for the Modeling of the Circumferential Stresses
Thomas, Jean-Philippe ULg; Léonard, Olivier ULg

in Journal of Turbomachinery (2012), 134(1),

Capturing a level of modeling of the flow inside a multi-stage turbomachine, such as unsteadiness for example, can be done at different degrees of details, either by capturing all deterministic features ... [more ▼]

Capturing a level of modeling of the flow inside a multi-stage turbomachine, such as unsteadiness for example, can be done at different degrees of details, either by capturing all deterministic features of the flow with a pure unsteady method or by settling for an approximated solution at a lower computational cost. The harmonic methods stand in this second category. Amongst them the "Nonlinear Harmonic Method'' from He revealed the most efficient. This method consists of solving the fully nonlinear 3D steady problem and a linearized perturbation system in the frequency domain. As it has been shown by the authors that the circumferential variations exhibit a harmonic behavior, it is proposed here to adapt this method to the throughflow model, where the main nonlinear system would be the common throughflow equations and the auxiliary system would give access to the circumferential stresses. As the numerical local explicit impermeability conditions are unsupported by Fourier series, the adaptation of this technique to the throughflow model passes through a reformulation of the blade effect by a smooth force field as in the "Immersed Boundary Method'' from Peskin. A simple example of an inviscid flow around a cylinder will illustrate the preceding developments, bringing back the mean effect of the circumferential non uniformities into the meridional flow. [less ▲]

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See detailTowards a High Order Throughflow. Part I : Investigating the Effectiveness of a Harmonic Reconstruction for 3D Flows
Thomas, Jean-Philippe ULg; Léonard, Olivier ULg

in Proceedings of the ASME Turbo Expo 2010 (2010, July)

The computation time and the extraction of useful information remain severe drawbacks to systematic use of modern three-dimensional Navier-Stokes codes in a design procedure of multistage turbomachines ... [more ▼]

The computation time and the extraction of useful information remain severe drawbacks to systematic use of modern three-dimensional Navier-Stokes codes in a design procedure of multistage turbomachines. That explains why throughflow simulation is still widely used at industrial scale. The main limitation of throughflow is however the need for empirical models to reproduce blade-flow interactions and major 3D flow features. The purpose of this work is to investigate the degree to which empiricism could be reduced by using the averaged-passage equations of Adamczyk, combined with a harmonic closure strategy. To that aim, results of a computation performed with a steady three-dimensional Navier-Stokes code are used to calculate some of the additional terms of the circumferentially-averaged equations, the so-called circumferential stresses. The importance of the latter to bring back the mean effect of circumferential non-uniformities, linked to 3D phenomena, is illustrated by injecting them into a throughfow simulation. Then the ability of truncated Fourier series to reproduce the level of non-uniformity in the core flow and near the walls is detailed. It is finally shown that the harmonic approximated stresses can lead to a good reproduction of local 3D flow features in throughflow simulation and to a better accuracy. [less ▲]

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See detailTowards a High Order Throughflow. Part II : Investigation of the Nonlinear Harmonic Method Coupled With an Immersed Boundary Method for the Modeling of the Circumferential Stresses
Thomas, Jean-Philippe ULg; Léonard, Olivier ULg

in Proceedings of the ASME Turbo Expo 2010 (2010, July)

Capturing a level of modeling of the flow inside a multi-stage turbomachine, such as unsteadiness for example, can be done at different degrees of details, either by capturing all deterministic features ... [more ▼]

Capturing a level of modeling of the flow inside a multi-stage turbomachine, such as unsteadiness for example, can be done at different degrees of details, either by capturing all deterministic features of the flow with a pure unsteady method or by settling for an approximated solution at a lower computational cost. The harmonic methods stand in this second category. Amongst them the "Nonlinear Harmonic Method'' from He revealed the most efficient. This method consists of solving the fully nonlinear 3D steady problem and a linearized perturbation system in the frequency domain. As it has been shown by the authors that the circumferential variations exhibit a harmonic behavior, it is proposed here to adapt this method to the throughflow model, where the main nonlinear system would be the common throughflow equations and the auxiliary system would give access to the circumferential stresses. As the numerical local explicit impermeability conditions are unsupported by Fourier series, the adaptation of this technique to the throughflow model passes through a reformulation of the blade effect by a smooth force field as in the "Immersed Boundary Method'' from Peskin. A simple example of an inviscid flow around a cylinder will illustrate the preceding developments, bringing back the mean effect of the circumferential non uniformities into the meridional flow. [less ▲]

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See detailFrom Manual to Model-Based Control of a Small Jet Engine
Léonard, Olivier ULg; Denis, François; Thomas, Jean-Philippe ULg et al

in Proceedings of the 19th ISABE Conference (2009, September)

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See detailOn the Role of the Deterministic and Circumferential Stresses in Throughflow Calculations
Simon, Jean-Francois; Thomas, Jean-Philippe ULg; Léonard, Olivier ULg

in Journal of Turbomachinery (2009), 131(3),

This paper presents a throughflow analysis tool developed in the context of the average-passage flow model elaborated by Adamczyk. The Adamczyk's flow model describes the 3D time-averaged flow field ... [more ▼]

This paper presents a throughflow analysis tool developed in the context of the average-passage flow model elaborated by Adamczyk. The Adamczyk's flow model describes the 3D time-averaged flow field within a blade row passage. The set of equations that governs this flow field is obtained by performing a Reynolds averaging, a time averaging, and a passage-to-passage averaging on the Navier–Stokes equations. The throughflow level of approximation is obtained by performing an additional circumferential averaging on the 3D average-passage flow. The resulting set of equations is similar to the 2D axisymmetric Navier–Stokes equations, but additional terms resulting from the averages show up: blade forces, blade blockage factor, Reynolds stresses, deterministic stresses, passage-to-passage stresses, and circumferential stresses. This set of equations represents the ultimate throughflow model provided that all stresses and blade forces can be modeled. The relative importance of these additional terms is studied in the present contribution. The stresses and the blade forces are determined from 3D steady and unsteady databases (a low-speed compressor stage and a transonic turbine stage) and incorporated in a throughflow model based on the axisymmetric Navier–Stokes equations. A good agreement between the throughflow solution and the averaged 3D results is obtained. These results are also compared to those obtained with a more “classical” throughflow approach based on a Navier–Stokes formulation for the endwall losses, correlations for profile losses, and a simple radial mixing model assuming turbulent diffusion. [less ▲]

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See detailTen Years of Experience With a Small Jet Engine as a Support for Education
Léonard, Olivier ULg; Borguet, Sébastien ULg; Thomas, Jean-Philippe ULg

in Journal of Engineering for Gas Turbines & Power (2009), 131(1),

In 1997 the Turbomachinery Group of the University of Liege decided to acquire a small jet engine to illustrate the courses in propulsion and to provide the students with the opportunity to get some ... [more ▼]

In 1997 the Turbomachinery Group of the University of Liege decided to acquire a small jet engine to illustrate the courses in propulsion and to provide the students with the opportunity to get some experience on data measurement, acquisition, and interpretation. Among others, the SR-30 engine from Turbine Technology Ltd. Chetek, WI was chosen. It consists of a single spool, single flow engine with a centrifugal compressor, a reversed combustion chamber an axial turbine, and a fixed convergent nozzle. This engine was installed on a test bench allowing for manual control and providing fuel and oil to the engine. The original setup included measurements of intercomponent pressure and temperatures, exhaust gas temperature, and rotational speed. Since then both the engine and the test bench have been deeply modified These modifications were led by a triple objective: the improvement and the enrichment of the measurement chain, the widening of the engine operational domain, and, last but not the least, the wish to offer appealing hands-on projects to the students. All these modifications were performed at the University of Liege and were conducted by the students as part of their Master theses. Several performance models of the engine were developed to support data validation and engine condition diagnostic. This paper summarizes the developments conducted with and by the students, and presents the experience that was gained by using this engine as a support for education. [less ▲]

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See detailInvestigation et modélisation des tensions circonférentielles en simulation méridienne
Thomas, Jean-Philippe ULg

Master of advanced studies dissertation (2008)

The computation time and the extraction of useful information remain severe drawbacks to systematic use of modern 3D Navier-Stokes codes in a design procedure of multistage turbomachines. That explains ... [more ▼]

The computation time and the extraction of useful information remain severe drawbacks to systematic use of modern 3D Navier-Stokes codes in a design procedure of multistage turbomachines. That explains why throughflow simulation is still widely used at industrial scale. The main limitation of throughflow is however the need for empirical models to reproduce blade-flow interactions and major 3D flow features. As an alternative, Adamczyk (1984) proposed three averaging operators (ensemble, time and passage) that lead to the average-passage model, linking the unsteady turbulent flow field to a steady flow field in a typical blade passage. This model involves additional terms that respectively bring back the mean effect of turbulence, deterministic unsteadiness and aperiodicity on the mean periodic flow. These terms need to be modelled; it is the closure problem. Harmonic closure, which consists in solving a linearized perturbation system in the frequency domain, revealed to be an efficient method to approximate deterministic stresses (He and Ning, 1998, Stridh, 2005, Vilmin, 2006). A fourth averaging can be performed, a circumferential averaging, giving rise to the throughflow model. Additional terms appear: the so-called circumferential stresses. It has been proven that these terms play an important role in the description of the flow (Jennions, 1986, Perrin, 1995), being at least as considerable as deterministic stresses. Introducing these terms in a throughflow simulation allows to reproduce the averaged 3D steady flow field (Simon, 2007). The purpose of this work is to investigate how far empiricism could be reduced by using the averaged-passage equations of Adamczyk, combined with a harmonic closure strategy. To that aim, in the first part of the work, results of a computation performed with a steady three-dimensional Navier-Stokes code are used to calculate the circumferential stresses. The importance of the latter to bring back the mean eff ect of circumferential non-uniformities, linked to 3D phenomena, is illustrated by injecting them into a throughfow simulation. Then the ability of truncated Fourier series to reproduce the flow and its level of non-uniformity in the core flow and near the hub and shroud walls is detailed. It is finally shown that the harmonic approximated stresses can lead to a good reproduction of local 3D flow features in throughflow simulation and to a better accuracy. In the second part of this work it is proposed to adapt the "Nonlinear Harmonic" method to the throughflow model, where the main non-linear system would be the common throughflow equations and the auxiliary systems would give access to a mean high order information; the circumferential stresses. On the way to the adaptation of this technique to the throughflow model, the work shows that a reformulation of the effect of the blades is needed. The latter cannot appear anymore as numerical local explicit impermeability conditions that could not be supported by Fourier series, needing a continuous circumferential evolution of the flow. To get rid of this issue, the blade effect is replaced by a smooth force field as in the "Immersed Boundary Method" of Peskin. A simple example of an inviscid flow around a cylinder illustrates the preceding developments, coupling the "Nonlinear Harmonic Method" to the "Immersed Boundary Method" in a throughflow model, to bring back the mean e ffect of the circumferential non uniformities into the meridional flow. [less ▲]

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See detailInvestigating Circumferential Non-Uniformities in Throughflow Calculations using an Harmonic Reconstruction
Thomas, Jean-Philippe ULg; Léonard, Olivier ULg

in Proceedings of the ASME Turbo Expo 2008 (2008, June)

The flow field in a multistage turbomachine is very complex. It is 3D, unsteady and turbulent. Even if modern simulation tools can describe most of the flow features, the computation time needed and the ... [more ▼]

The flow field in a multistage turbomachine is very complex. It is 3D, unsteady and turbulent. Even if modern simulation tools can describe most of the flow features, the computation time needed and the extraction of useful information remain severe drawbacks to systematic use of URANS codes in a design procedure. In this context the throughflow simulation proved to be more convenient. Nevertheless the need for empiricism limits the potential of throughflow solvers. As an alternative, Admaczyck (1984) proposed three averaging operators (ensemble, time and passage) that lead to the average-passage model, linking the unsteady turbulent flow field to a steady flow field in a typical blade passage. This model involves additional terms that respectively bring back the mean effect of turbulence, deterministic unsteadiness and aperiodicity on the mean periodic flow. These terms need to be modelled; it is the closure problem. Harmonic closure, which consists in solving a linearized perturbation system in the frequency domain, revealed to be an efficient method to approximate deterministic stresses (He and Ning, 1998, Stridh, 2005, Vilmin, 2006). A fourth averaging can be performed, a circumferential averaging, giving rise to the throughflow model. Additional terms appear: the so-called circumferential stresses. It has been proven that these terms play an important role in the description of the flow (Jennions, 1986, Perrin, 1995), being at least as considerable as deterministic stresses. Introducing these terms in a throughflow simulation allows to reproduce the averaged 3D steady flow field (Simon, 2007). The aim of the present contribution is to prove that harmonic method can potentially be used to reconstruct circumferential stresses. The importance of circumferential stresses in a throughflow simulation is first highlighted on a single stage low speed compressor testcase, for viscous and non-viscous flow fields. The second step is the characterization of the frequency spectrum of the circumferential perturbation field. Next are compared the stresses associated to a Fourier reconstruction of the perturbation field with the real ones. Finally the approximated circumferential stresses are injected into a throughflow simulation tool to analyse and demonstrate their capability to reproduce a 3D averaged flow field. [less ▲]

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See detailContrôle d'un turboréacteur au banc d'essai sur base d'une modélisation en régime transitoire
Thomas, Jean-Philippe ULg

Master's dissertation (2005)

Le service de Turbomachines et Propulsion de l'Université de Liège dispose depuis plusieurs années d'un turboréacteur de laboratoire. Celui-ci consiste en un outil à vocation pédagogique très précieux, et ... [more ▼]

Le service de Turbomachines et Propulsion de l'Université de Liège dispose depuis plusieurs années d'un turboréacteur de laboratoire. Celui-ci consiste en un outil à vocation pédagogique très précieux, et c'est dans ce cadre que ce travail fut réalisé. L'objectif majeur de cette étude était la synthèse et l'application d'un contrôleur digital analogue aux systèmes en usage dans l'aviation civile et militaire. Pour atteindre ce but, plusieurs étapes furent nécessaires. Avant cette entreprise, le banc d'essai disposait d'une mesure de la poussée, effet utile du moteur, fortement parasitée par l'ajout de divers dispositifs au cours des années. Cette mesure étant une information importante, notamment en vue d'une modélisation, et l'effet régulé, il fut nécessaire d'améliorer le système existant. Ceci fut réalisé par une démarche technique complète. Un étalonnage du dispositif fut effectué et montra une pleine satisfaction de l'objectif. L'étape suivante fut la modélisation du moteur, pré-requis à toute étude ultérieure. Par une prise en compte des particularités de celui-ci, cette modélisation montra, après un recalage sur base de mesures prises au banc d'essai, une très bonne qualité de prédiction en régime stationnaire. Son extension au régime transitoire permit de modéliser précisément la dynamique liée à la vitesse de rotation. Celle des autres grandeurs fut par contre quantitativement déficiente mais qualitativement cohérente, en traduisant correctement le comportement physique de chacune. Il fut dès lors possible d'exploiter ce modèle pour la synthèse d'un régulateur. Le contrôleur devait répondre à deux objectifs: la diminution du temps de réponse et le respect des limites physiques du moteur. Ceci fut réalisé par la synthèse d'un régulateur comprenant une série de boucles SISO (Single Input Single Output): l'une gérant le contrôle sur la poussée et les autres garantissant chacune le respect d'une limite. L'utilisation de ce dispositif sur le modèle permit la satisfaction des objectifs, y compris en présence de bruit de mesure. La dernière étape du travail devait être l'application de ce contrôleur au banc d'essai. Celui-ci révéla cependant une telle inadaptation à un contrôle précis et rapide que l'objectif dû être orienté vers un contrôle plus simple, éloigné de la théorie précédente, qui autorisa néanmoins un suivi de consigne satisfaisant. Cette démarche permit malgré tout de mettre en exergue les déficiences du banc d'essai en vue d'une amélioration future conséquente, afin de permettre l'application de la théorie développée et d'ouvrir une porte vers un approfondissement du contrôle. [less ▲]

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