Inlet flow distortion is a non-uniform total pressure, total temperature, or swirl (flow angularity) condition at an aircraft engine inlet. Inlet distortion is a critical consideration in modern fan and compressor design. This is especially true as the industry continues to increase the efficiency and operating range of air breathing gas turbine engines. The focus of this paper is to evaluate the Computational Fluid Dynamics (CFD) Harmonic Balance (HB) solver in STAR-CCM+ as a reduced order method for capturing inlet distortion as well as the associated distortion transfer and generation. New methods for quantitatively describing and analyzing distortion transfer and generation are investigated. The geometry used is the rotor 4 fan geometry, consisting of one rotor and one stator. The inlet boundary condition is a 90-degree sector total pressure distortion profile with total pressure and swirl held constant. Multiple HB simulations with varying mode combinations and distortion intensities are analyzed and compared against full annulus Unsteady Reynolds Averaged Navier-Stokes (URANS) simulations. Best practices and recommendations for the implementation of the HB solver are given. The pre-existing Society of Automotive Engineers Aerospace Recommended Practice (SAE-ARP) 1420b descriptors are demonstrated to be inadequate for the purposes of analyzing distortion transfer and generation on a stage-to-stage basis. New implementations of Fourier methods are presented as an alternative to the SAE-ARP 1420b descriptors. These Fourier descriptors are shown to describe distortion transfer and generation to a higher degree of fidelity than the SAE-ARP 1420b descriptors. These new descriptors are demonstrated on the analysis of full annulus URANS and HB simulations. The HB solver is shown to be capable of capturing distortion transfer, generation and performance degradation. Recommendations for the optimal implementation of the HB method are given.

The continuous trend in gas turbine design towards lighter, more powerful and more reliable engines on one side and use of alternative fuels on the other side renders flutter problems as one of the paramount challenges in engine design. Flutter denotes a self-excited and self-sustained aeroelastic instability phenomenon that can lead to material fatigue and eventually damage of structure in a short period of time unless properly damped. The design for flutter safety involves the prediction of unsteady aerodynamics as well as structural dynamics that is mostly based on in-house developed numerical tools. While high confidence has been gained on the structural side unanticipated flutter occurrences during engine design, testing and operation evidence a need for enhanced validation of aerodynamic models despite the degree of sophistication attained. The continuous development of these models can only be based on the deepened understanding of underlying physical mechanisms from test data. As a matter of fact most flutter test cases treat the turbomachine flow in two-dimensional manner indicating that the problem is solved as plane representation at a certain radius rather than representing the complex annular geometry of a real engine. Such considerations do consequently not capture effects that are due to variations in the third dimension, i.e. in radial direction. In this light the present thesis has been formulated to study three-dimensional effects during flutter in the annular environment of a low-pressure turbine blade row and to describe the importance on prediction of flutter stability. The work has been conceived as compound experimental and computational work employing a new annular sector cascade test facility. The aeroelastic response phenomenon is studied in the influence coefficient domain having one blade oscillating in various three-dimensional rigid-body modes and measuring the unsteady response on several blades and at various radial positions. On the computational side a state-of-the-art industrial numerical prediction tool has been used that allowed for two-dimensional and three-dimensional linearized unsteady Euler analyses. The results suggest that considerable three-dimensional effects are present, which are harming prediction accuracy for flutter stability when employing a two-dimensional plane model. These effects are mainly apparent as radial gradient in unsteady response magnitude from tip to hub indicating that the sections closer to the hub experience higher aeroelastic response than their equivalent plane representatives. Other effects are due to turbomachinery-typical three-dimensional flow features such as hub endwall and tip leakage vortices, which considerably affect aeroelastic prediction accuracy. Both effects are of the same order of magnitude as effects of design parameters such as reduced frequency, flow velocity level and incidence. Although the overall behavior is captured fairly well when using two-dimensional simulations notable improvement has been demonstrated when modeling fully three-dimensional and including tip clearance.

The design parameters axial gap and stator count of highpressure turbine stages are evaluated numerically towards theirinfluence on the unsteady aerodynamic excitation of rotorblades. Of particular interest is if and how unsteadyaerodynamic considerations in the design could reduce the riskofhigh cycle fatigue (HCF) failures of the turbine rotor. A well-documented 2D/Q3D non-linear unsteady code (UNSFLO)is chosen to perform the stage flow analyses. The evaluatedresults are interpreted as aerodynamic excitation mechanisms onstream sheets neglecting 3D effects. Mesh studies andvalidations against measurements and 3D computations provideconfidence in the unsteady results. Three test cases areanalysed. First, a typical aero-engine high pressure turbinestage is studied at subsonic and transonic flow conditions,with four axial gaps (37% - 52% of cax,rotor) and two statorconfigurations (43 and 70 NGV). Operating conditions areaccording to the resonant conditions of the blades used inaccompanied experiments. Second, a subsonic high pressureturbine intended to drive the turbopump of a rocket engine isinvestigated. Four axial gap variations (10% - 29% ofcax,rotor) and three stator geometry variations are analysed toextend and generalise the findings made on the first study.Third, a transonic low pressure turbine rotor, known as theInternational Standard Configuration 11, has been modelled tocompute the unsteady flow due to blade vibration and comparedto available experimental data. Excitation mechanisms due to shock, potential waves andwakes are described and related to the work found in the openliterature. The strength of shock excitation leads to increasedpressure excitation levels by a factor 2 to 3 compared tosubsonic cases. Potential excitations are of a typical wavetype in all cases, differences in the propagation direction ofthe waves and the wave reflection pattern in the rotor passagelead to modifications in the time and space resolved unsteadypressures on the blade surface. The significant influence ofoperating conditions, axial gap and stator size on the wavepropagation is discussed on chosen cases. The wake influence onthe rotorblade unsteady pressure is small in the presentevaluations, which is explicitly demonstrated on the turbopumpturbine by a parametric study of wake and potentialexcitations. A reduction in stator size (towards R≈1)reduces the potential excitation part so that wake andpotential excitation approach in their magnitude. Potentials to reduce the risk of HCF excitation in transonicflow are the decrease of stator exit Mach number and themodification of temporal relations between shock and potentialexcitation events. A similar temporal tuning of wake excitationto shock excitation appears not efficient because of the smallwake excitation contribution. The increase of axial gap doesnot necessarily decrease the shock excitation strength neitherdoes the decrease of vane size because the shock excitation mayremain strong even behind a smaller stator. The evaluation ofthe aerodynamic excitation towards a HCF risk reduction shouldonly be done with regard to the excited mode shape, asdemonstrated with parametric studies of the mode shapeinfluence on excitability. <b>Keywords:</b>Aeroelasticity, Aerodynamics, Stator-RotorInteraction, Excitation Mechanism, Unsteady Flow Computation,Forced Response, High Cycle Fatigue, Turbomachinery,Gas-Turbine, High-Pressure Turbine, Turbopump, CFD, Design

An approach was developed which allows for design studies of commercial aircraft using physics-based noise analysis methods while retaining the ability to perform the rapid tradeoff and risk analysis studies needed at the conceptual design stage. A prototype integrated analysis process was created for computing the total aircraft EPNL at the Federal Aviation Regulations Part 36 certification measurement locations using physics-based methods for fan rotor-stator interaction tones and jet mixing noise. The analysis process was then used in combination with design of experiments to create response surface equations (RSEs) for the engine and aircraft performance metrics, geometric constraints and takeoff and landing noise levels. In addition, Monte Carlo analysis was used to assess the expected variability of the metrics under the influence of uncertainty, and to determine how the variability is affected by the choice of engine cycle. Finally, the RSEs were used to conduct a series of proof-of-concept conceptual-level design studies demonstrating the utility of the approach. The study found that a key advantage to using physics-based analysis during conceptual design lies in the ability to assess the benefits of new technologies as a function of the design to which they are applied. The greatest difficulty in implementing the physics-based analysis proved to be the generation of design geometry at a sufficient level of detail for high-fidelity analysis.

Static characteristics and rotordynamic coefficients were experimentally determined for a four-pad tilting-pad journal bearing with ball-in-socket pivots in loadbetween- pad configuration. A frequency-independent [M]-[C]-[K] model fit the measurements reasonably well, except for the cross-coupled damping coefficients. Test conditions included speeds from 4,000 to 12,000 rpm and unit loads from 0 to 1896 kPa (0 to 275 psi). The test bearing was manufactured by Rotating Machinery Technology (RMT), Inc. Though it has a nominal diameter of 101.78 mm (4.0070 in.), measurements indicated significant bearing crush with radial bearing clearances of 99.6 μm (3.92 mils) and 54.6 μm (2.15 mils) in the axes 45º counterclockwise and 45º clockwise from the loaded axis, respectively. The pad length is 101.6 mm (4.00 in.), giving L/D = 1.00. The pad arc angle is 73º, and the pivot offset ratio is 65%. The preloads of the loaded and unloaded pads are 0.37 and 0.58, respectively. A bulk-flow Navier-Stokes model was used for predictions, using adiabatic conditions for the bearing fluid. Because the model assumes constant nominal clearances at all pads, the average of the measured clearances was used as an estimate. Eccentricities and attitude angles were markedly under predicted while power loss was under predicted at low speeds and very well predicted at high speeds. The maximum detected pad temperature was 71ºC (160ºF) and the rise from inlet to maximum bearing temperature was over predicted by 10-40%. Multiple-frequency force inputs were used to excite the bearing. Direct stiffness and damping coefficients were significantly over predicted, but addition of a simple stiffness-in-series model substantially improved the agreement between theory and experiment. Direct added masses were zero or negative at low speeds and increased with speed up to a maximum of about 50 kg; they were normally greater in the unloaded direction. Although significant cross-coupled stiffness terms were present, they always had the same sign. The bearing had zero whirl frequency ratio netting unconditional stability over all test conditions. Static stiffness in the y direction (obtained from steadystate loading) matched the rotordynamic stiffness Kyy (obtained from multiple-frequency excitation) reasonably at low loads but poorly at the maximum test load.

<p>The design parameters axial gap and stator count of highpressure turbine stages are evaluated numerically towards theirinfluence on the unsteady aerodynamic excitation of rotorblades. Of particular interest is if and how unsteadyaerodynamic considerations in the design could reduce the riskofhigh cycle fatigue (HCF) failures of the turbine rotor.</p><p>A well-documented 2D/Q3D non-linear unsteady code (UNSFLO)is chosen to perform the stage flow analyses. The evaluatedresults are interpreted as aerodynamic excitation mechanisms onstream sheets neglecting 3D effects. Mesh studies andvalidations against measurements and 3D computations provideconfidence in the unsteady results. Three test cases areanalysed. First, a typical aero-engine high pressure turbinestage is studied at subsonic and transonic flow conditions,with four axial gaps (37% - 52% of cax,rotor) and two statorconfigurations (43 and 70 NGV). Operating conditions areaccording to the resonant conditions of the blades used inaccompanied experiments. Second, a subsonic high pressureturbine intended to drive the turbopump of a rocket engine isinvestigated. Four axial gap variations (10% - 29% ofcax,rotor) and three stator geometry variations are analysed toextend and generalise the findings made on the first study.Third, a transonic low pressure turbine rotor, known as theInternational Standard Configuration 11, has been modelled tocompute the unsteady flow due to blade vibration and comparedto available experimental data.</p><p>Excitation mechanisms due to shock, potential waves andwakes are described and related to the work found in the openliterature. The strength of shock excitation leads to increasedpressure excitation levels by a factor 2 to 3 compared tosubsonic cases. Potential excitations are of a typical wavetype in all cases, differences in the propagation direction ofthe waves and the wave reflection pattern in the rotor passagelead to modifications in the time and space resolved unsteadypressures on the blade surface. The significant influence ofoperating conditions, axial gap and stator size on the wavepropagation is discussed on chosen cases. The wake influence onthe rotorblade unsteady pressure is small in the presentevaluations, which is explicitly demonstrated on the turbopumpturbine by a parametric study of wake and potentialexcitations. A reduction in stator size (towards R≈1)reduces the potential excitation part so that wake andpotential excitation approach in their magnitude.</p><p>Potentials to reduce the risk of HCF excitation in transonicflow are the decrease of stator exit Mach number and themodification of temporal relations between shock and potentialexcitation events. A similar temporal tuning of wake excitationto shock excitation appears not efficient because of the smallwake excitation contribution. The increase of axial gap doesnot necessarily decrease the shock excitation strength neitherdoes the decrease of vane size because the shock excitation mayremain strong even behind a smaller stator. The evaluation ofthe aerodynamic excitation towards a HCF risk reduction shouldonly be done with regard to the excited mode shape, asdemonstrated with parametric studies of the mode shapeinfluence on excitability.</p><p><b>Keywords:</b>Aeroelasticity, Aerodynamics, Stator-RotorInteraction, Excitation Mechanism, Unsteady Flow Computation,Forced Response, High Cycle Fatigue, Turbomachinery,Gas-Turbine, High-Pressure Turbine, Turbopump, CFD, Design</p>

Les motoristes aéronautiques souhaitent disposer de la représentation la plus fidèle possible du fonctionnement des propulseurs, dans une perspective d'amélioration continue de leurs performances. Les modèles numériques doivent donc intégrer au maximum les détails géométriques susceptibles d'influencer la physique de l'écoulement analysé. La prise en compte de tels effets technologiques s'avère difficile dans le contexte des solveurs structurés disponibles.Une stratégie hybride de prise en compte des effets technologiques fait coexister au sein d'un même domaine de calcul des zones structurées et non structurées. La flexibilité de génération d'un maillage non structuré permet une prise en compte aisée des détails géométriquement complexes tandis que la préservation de zones structurées dans une majeure partie du domaine de calcul permet de bénéficier de l'efficacité d'un solveur structuré. La présente thèse contribue au développement de cette stratégie hybride au sein du solveur elsA de l'ONERA en proposant des gains de précision et de robustesse par rapport à la version initialement développée pour établir la faisabilité et l'intérêt de l'approche. Après un état de l'art des techniques de discrétisation spatiale disponibles dans cette version initiale, différentes améliorations (techniques de moindres carrés, approche dite quasi-Green, méthode d'estimation des gradients aux faces) ont été analysées puis implémentées et validées sur des cas académiques. Le choix d'une stratégie hybride avec raccords coïncidents entre zones structurées et non-structurées conduit à des déformations de maillage dans la zone d'interface structuré / non-structuré qui ont exigé le développement supplémentaire de techniques d'amélioration de la robustesse (limiteurs physiques ou géométriques). Le solveur hybride rassemblant ces différentes fonctionnalités a permisde simuler avec succès des géométries d'aubes isolées dotées d'effets technologiques tels que congé de raccordement, trous de refroidissement, fentes de bord de fuite, cheminées internes d'alimentation. Enfin, une stratégie permettant l'utilisation de l'approche hybride en étage complet a été proposée et appliquée à la simulation hybride de l'interaction rotor/stator pour la configuration VKI-BRITE CT3, en stationnaire et en instationnaire, respectivement via une condition de plan de mélange et une condition de chorochronicité. / The aerospace engine manufacturers wish to rely on the most accurate description of their propulsion systems in order to continuously improve their performance levels. Therefore, numerical models must include as much as possible geometrical details likely to impact the physics of the flow under study. Taking into account such technological effects turns out to be a difficult task when working with available structured solvers. A hybrid strategy takes advantage of structured and unstructured zones within the same computational domain in order to efficiently describe technological effects. Geometrically complex local details are easily accounted for thanks to the flexibility of unstructured grid generation while keeping structured zones in the remainder of the flow domain allows to benefit from the tried and tested structured solver efficiency. The present work contributes to the development of such a hybrid strategy in ONERA elsA solver and enhances accuracy and robustness with respect to the solver initially developed to establish the feasibility and interest of hybridization. Following a review of the space discretization techniques available in the initial solver, several improvements (least square techniques, quasi-Green approach, computation of face gradients) have been analysed, then implemented and validated for academic test-cases. The choice of a hybrid strategy with coincident matching between structured and unstructured zones leads to highly deformed cells in the structured / unstructured interface region, requiring the development of supplementary robustness improvement techniques (physics- or geometry-based limiters). The hybrid solver gathering these various options allows to successfully compute isolated blade geometries including technological effects such as blade fillet, cooling holes, trailing edge cutbacks, internal coolant supply channel. Finally, a structured / unstructured strategy has been proposed and applied to the hybrid simulation of a rotor/stator interaction for the steady and unsteady

Dans les turbomachines conventionnelles, l’estimation des performances (rendement, puissance et rapport de pression) se fait en général en admettant l’adiabaticité de l’écoulement. Mais, de nombreuses études ayant montré l’influence négative des échanges thermiques internes et externes sur les performances des petites turbomachines dans les faibles charges et aux bas régimes, cette hypothèse ne peut plus être recevable. L’objectif principal de cette thèse est de contribuer à lever l’hypothèse d’adiabaticité.Une étude préalable de l’état de l’art a permis de relever les différents types de transferts thermiques dans les turbomachines et de circonscrire notre étude.Puis, une analyse exergétique généralisée, ayant pour but la prise en compte des deux principes de la thermodynamique, a été effectuée et l’évolution de l’indice de performance caractérisant le niveau d’énergie récupérable en fonction des échanges thermiques est étudiée.Les performances des turbomachines à fluide compressible sont généralement représentées sous forme graphique dans des systèmes de coordonnées adimensionnelles établies avec l’hypothèse d’adiabaticité. Ces cartographies couramment utilisées par les exploitants et constructeurs ne conviennent pas aux machines fonctionnant avec transferts thermiques. L’étude de la similitude des turbomachines thermiques à fluide compressible présentée dans ce travail, propose de nouvelles coordonnées adimensionnelles pouvant être utilisées aussi bien en adiabatique que dans les écoulements avec transferts thermiques.Enfin, nous proposons un protocole de mesures et un modèle numérique pour l’évaluation des transferts thermiques dans un turbocompresseur.Certains résultats obtenus montrent que les performances calculées avec l’hypothèse d’adiabaticité de l’écoulement du fluide sont surestimées. Les nouvelles lois de la similitude proposées généralisent le théorème de Rateau au fluide compressible fonctionnant dans n’importe quelle condition et permettent de calculer les échanges thermiques à chaud à partir des résultats d’essai à froid. Une donnée supplémentaire (température de refoulement) est néanmoins nécessaire pour la prédiction complète des performances et des échanges thermiques.Le modèle numérique de calcul des échanges thermiques proposé donne des résultats en accord avec ceux attendus, mais nécessite des données réelles issues de mesure sur banc pour une validation complète. / In the conventional turbomachines, calculations are done assuming adiabatic flow. But, the negative influence of external and internal heat exchange on the performance of small turbomachines at low loads and low speeds have been shown by many studies in the literature. Then, this assumption is no longer admissible. The main objective of this thesis is to help remove the assumption of adiabaticity.A study of the state of art has identified the different kinds of heat transfer and defined the limits of our investigations.Afterwards, a generalized exergy analysis whose main goal is to take into account the two principles of thermodynamics has been made and the variation of exergy performance versus heat transfer has been studied.The maps currently used are made with the assumption of adiabaticity. The laws of similarity in turbomachines working with compressible fluid studied propose new dimensionless coordinates that can be used in any operating condition (adiabatic or not).Finally, we present a measurement protocol and a numerical model for calculating heat transfer in a turbocharger.Some results from our work indicate that the performance of thermal turbomachinery announced regardless of thermal heat exchanges are found to be overestimated.The new laws of similarity proposed generalize the Rateau’s theorem to compressible fluid flow in any operating condition and can be used to calculate heat transfer from adiabatic test results. Supplementary information is still required for the complete prediction of performance and heat transfer.The numerical model for calculating heat transfer gives some results that are in agreement with those expected. But actual data from test bench are required for complete validation.

La thèse est consacrée à la modélisation et à l'analyse par voie numérique de l'écoulement dans une pompe à vide turbomoléculaire hybride, combinant une succession d'étages de type rotor et stator et un Holweck. Une approche de type Test Particle Monte Carlo 3D a été développée pour des configurations de pompes industrielles (géométries complexes d'aubes, gestion des étages rotor et stator) dans un souci d'optimisation des coûts de simulation. L'outil numérique développé a été validé pour des configurations académiques et industrielles, en s'appuyant notamment sur des résultats expérimentaux obtenus grâce au banc d'essai de l'entreprise aVP. L'apport de l'approche TPMC3D par rapport aux méthodes de design disponibles en début de thèse a été clairement démontré pour le régime moléculaire libre. Quelques préconisations de design ont également pu être formulées en utilisant le code développé. Le potentiel d'une approche de type Direct Simulation Monte Carlo, prenant en compte les interactions entre molécules du gaz, a également été établi en 2D pour le régime de transition. / The thesis is devoted to the modeling and the numerical analysis of the flow in a turbomolecular vacuum pump of hybrid type, that is combining a succession of rotor and stator stages with an Holweck. A 3D Test Particle Monte Carlo approach has been developed for simulating industrial pump configurations (complex blade geometries, management of rotor and stator stages), with attention paid to the optimization of the computational cost. The numerical tool developed in the thesis has been validated for academic and industrial test cases, relying in particular on reference experimental results obtained on the test rig of the aVP company. The prediction improvement brought by the TPMC 3D approach with respect to the design tools available at the start of the thesis has been clearly demonstrated for the free molecular flow regime. Some design recommendations have also been formulated using the developed solver. The potential of a Direct Simulation Monte Carlo approach, taking into account the interactions between gas molecules, has also been established in 2D for the transition regime.

Le développement de turbomachines à faible vitesse spécifique suscite actuellement une forte demande dans de nombreux domaines industriels. De nos jours, les ventilateurs centrifuges constituées d'une roue, d'un diffuseur et d'un canal de retour sont largement utilisés dans de nombreuses applications telles que l'automobile, l'aéronautique, appareils domestiques, etc. En raison de leur grande adaptabilité, ils peuvent fonctionner sur une large plage de débit en particulier avec une vitesse de rotation importante. Cependant, leur utilisation nécessite une meilleure compréhension de leur fonctionnement et notamment de l'interaction rotor-stator pour mieux les concevoir. L'objectif de cette étude est d'analyser et de quantifier l'influence de la solidité des aubes du diffuseur (ou serrage des profils) sur les performances aérauliques du ventilateur centrifuge. Une étude numérique et expérimentale a été menée pour analyser les performances d'un ventilateur centrifuge avec différents niveaux d'interaction rotor-stator. Différentes géométries de diffuseur ont été proposées dans le but de réduire les dissipations énergétiques liées aux phénomènes de recirculation et aux forces de viscosité. L'étude approfondie de la norme ISO 5801 et ISO 5167 a permis de dimensionner et réaliser le banc d'essai et les organes de mesures. Ces normes proposent des calculs et des spécifications qui nous ont permis de fixer des critères quant au choix des éléments du banc d’essai AERO2VACCUM. / Nowadays, centrifugal fans are widely used in many industrial applications such as automotive, aeronautic, vacuum cleaner, etc. Due to their high adaptability, they can operate over a wide flow range especially with high speed rotation. In order to reduce the impact on environment, centrifugal fan as other energy conversion system has to display a high efficiency. However, a better understanding of their working and of the rotor-stator interaction is required to enhance their design and to make them widely integrated in current applications. The purpose of this study is to analyze and to quantify the influence of the solidity vaned diffusers on the performance of a centrifugal fan. A computational study has been conducted to analyze the performance of a centrifugal fan under various levels of impeller-diffuser interactions. The objective was to understand the pressure recovery phenomena in each diffuser. Different geometries were proposed to reduce both separation flow phenomenon and viscous losses. The geometries are all composed with the same impeller and return channel, only the vaned diffusers differ; the trailing edges are maintained at the same position while the leading edges have different radial positions. The characterization of the fan has been realized by an experimental setup designed and built in agreement to the standards ISO 5801 and 516