La modélisation par simulation des grandes échelles (Large-Eddy Simulation - LES) des processus physiques régissant la couche limite atmosphérique (CLA) demeure complexe de part la difficulté des modèles à capter l'évolution de la turbulence entre différentes conditions de stratification. De ce fait, l'étude LES du cycle diurne complet de la CLA comprenant des situations convectives la journée et des conditions stables la nuit est très peu documenté. La simulation de la couche limite stable où la turbulence est faible, intermittente et qui est caractérisée par des structures turbulentes de petite taille est tout particulièrement compliquée. En conséquence, la capacité de la LES à bien reproduire les conditions météorologiques de la CLA, notamment en situation stable, est étudiée à l'aide du code de mécanique des fluides développé par EDF R&D, Code_Saturne. Dans une première étude, le modèle LES est validé sur un cas de couche limite convective quasi stationnaire sur terrain homogène. L'influence des modèles sous-maille de Smagorinsky, Germano-Lilly, Wong-Lilly et WALE (Wall-Adapting Local Eddy-viscosity) ainsi que la sensibilité aux méthodes de paramétrisation sur les champs moyens, les flux et les variances est discutées. Dans une seconde étude le cycle diurne complet de la CLA pendant la campagne de mesure Wangara est modélisé. L'écart aux mesures étant faible le jour, ce travail se concentre sur les difficultés rencontrées la nuit à bien modéliser la couche limite stable. L'impact de différents modèles sous-maille ainsi que la sensibilité au coefficient de Smagorinsky ont été analysés. Par l'intermédiaire d'un couplage radiatif réalisé en LES, les répercussions du rayonnement infrarouge et solaire sur le jet de basse couche nocturne et le gradient thermique près de la surface sont exposées. De plus l'adaptation de la résolution du domaine à l'intensité de la turbulence et la forte stabilité atmosphérique durant l'expérience Wangara sont commentées. Enfin un examen des oscillations numériques inhérentes à Code_Saturne est réalisé afin d'en limiter les effets / Large-eddy simulation (LES) of the physical processes in the atmospheric boundary layer (ABL) remains a complex subject. LES models have difficulties to capture the evolution of the turbulence in different conditions of stratification. Consequently, LES of the whole diurnal cycle of the ABL including convetive situations in daytime and stable situations in the night time is seldom documented. The simulation of the stable atmospheric boundary layer which is characterized by small eddies and by weak and sporadic turbulence is espacialy difficult. Therefore The LES ability to well reproduce real meteorological conditions, particularly in stable situations, is studied with the CFD code developed by EDF R&D, Code_Saturne. The first study consist in validate LES on a quasi-steady state convective case with homogeneous terrain. The influence of the subgrid-scale models (Smagorinsky model, Germano-Lilly model, Wong-Lilly model and Wall-Adapting Local Eddy-viscosity model) and the sensitivity to the parametrization method on the mean fields, flux and variances are discussed.In a second study, the diurnal cycle of the ABL during Wangara experiment is simulated. The deviation from the measurement is weak during the day, so this work is focused on the difficulties met during the night to simulate the stable atmospheric boundary layer. The impact of the different subgrid-scale models and the sensitivity to the Smagorinsky constant are been analysed. By coupling radiative forcing with LES, the consequences of infra-red and solar radiation on the nocturnal low level jet and on thermal gradient, close to the surface, are exposed. More, enhancement of the domain resolution to the turbulence intensity and the strong atmospheric stability during the Wangara experiment are analysed. Finally, a study of the numerical oscillations inherent to Code_Saturne is realized in order to decrease their effects

Neste trabalho foi realizado um estudo utilizando os modelos de turbulência Simulação das Grandes Escalas, Large Eddy Simulation (LES), e Simulação dos Vórtices Desprendidos, Detached Eddy Simulation (DES), para simular o escoamento compressível interno em um duto contendo válvulas controladoras na saída dos gases de combustão de um reator de craqueamento catalítico fluido, com o objetivo de comparar o desempenho numérico e computacional de ambas as técnicas. Para isso foi utilizado um programa comercial de dinâmica dos fluidos computacional, Computational Fluid Dynamics (CFD), que possui em seu código os dois modelos de turbulência. / In the present work a study was conducted using Large Eddy Simulation (LES) and Detached Eddy Simulation (DES) turbulence models in order to simulate the internal compressible flow in a duct containing the flue gas discharge control valves of a fluid catalytic cracking reactor so as to compare the numerical and computational behavior of both techniques. A commercial Computational Fluid Dynamics (CFD) software, which includes these turbulence models in its code, was used.

Les orages tropicaux jouent un rôle incertain dans le transport de l'air troposphérique dans la stratosphère limitant notre capacité à prévoir le climat futur. Le transport par les orages pourrait en effet être sous-estimé dans les modèles de climat aux résolutions trop grossières. L'efficacité de ce transport est analysée à partir de simulations numériques de l'orage Hector the Convector jusqu'à une résolution de 100 m, la plus fine jamais utilisée pour un cas de convection très profonde. Les percées nuageuses, qui avaient été observées à son sommet à 18 km d'altitude, sont reproduites et l'hydratation nette de la stratosphère est quantifiée. La contribution des orages tropicaux au flux d'eau de la troposphère à la stratosphère est ainsi estimée à près de 20 %. La quasi-convergence aux résolutions de 200 m et 100 m suggère que de telles résolutions sont nécessaires pour représenter correctement les ascendances. L'analyse individuelle des ascendances indique que les deux plus grandes contribuent à plus de 90 % du flux de masse vers la basse stratosphère. Elles sont plus larges, plus puissantes et contiennent plus d'eau que les plus grandes ascendances une heure avant et une heure après, et leur cœur convectif apparaît très peu dilué. L'alimentation en surface par des lignes de convergence intensifiées par des poches froides et la faible dilution des deux plus grandes ascendances sont déterminantes dans l'apparition de la convection très profonde. L'analyse isentropique de la circulation générale dans Hector confirme le flux de masse calculé par l'analyse des ascendances. Elle le corrige dans les basses couches en prenant en compte les flux turbulents, et en haute troposphère en filtrant les ondes de gravité. Elle met en évidence l'importance du dégagement de chaleur latente dû à la congélation dans les plus grandes ascendances pendant la phase de percée en stratosphère. / The tropical thunderstorms play an uncertain role in the transport of tropospheric air into the stratosphere, limiting our capability to predict the future climate. The transport by the thunderstorms may be underestimated by the climate models, due to their coarse resolutions. The efficiency of this transport is analysed using numerical simulations of the thunderstorm Hector the Convector with resolutions down to 100 m, the finest ever used for a case of very deep convection. The overshoots, that were observed at its top at 18 km altitude, are captured and the net hydration of the stratosphere is quantified. The contribution of the tropical thunderstorms to the water flux from the troposphere to the stratosphere is then estimated to about 20 %. The almost convergence at 200 m and 100 m suggests that such resolutions are necessary to correctly represent the updafts. The individual analysis of the updrafts indicates that the two tallest contribute beyond 90 % of the mass flux into the stratosphere. They are larger, more vigorous and contain more water than the tallest updrafts one hour before and one hour after, and their convective core was weakly diluted. The supply from the surface by the convergence lines, intensified by the cold pools, and the weak dilution of the two tallest updrafts are determinant for the development of very deep convection. The isentropic analysis of the overturning inside Hector confirms the mass flux computed with the updrafts analysis. It corrects the estimate in the lower troposphere by taking into account the turbulent flux, and in the upper troposphere by filtering out the gravity waves. It highlights the importance of the latent heating due to freezing in the two tallest updrafts during the phase of overshoot in the stratosphere.

Neste trabalho foi realizado um estudo utilizando os modelos de turbulência Simulação das Grandes Escalas, Large Eddy Simulation (LES), e Simulação dos Vórtices Desprendidos, Detached Eddy Simulation (DES), para simular o escoamento compressível interno em um duto contendo válvulas controladoras na saída dos gases de combustão de um reator de craqueamento catalítico fluido, com o objetivo de comparar o desempenho numérico e computacional de ambas as técnicas. Para isso foi utilizado um programa comercial de dinâmica dos fluidos computacional, Computational Fluid Dynamics (CFD), que possui em seu código os dois modelos de turbulência. / In the present work a study was conducted using Large Eddy Simulation (LES) and Detached Eddy Simulation (DES) turbulence models in order to simulate the internal compressible flow in a duct containing the flue gas discharge control valves of a fluid catalytic cracking reactor so as to compare the numerical and computational behavior of both techniques. A commercial Computational Fluid Dynamics (CFD) software, which includes these turbulence models in its code, was used.

Turbulence is an open and challenging problem for mathematical approaches, physical modeling and numerical simulations. Numerical solutions contribute significantly to the understand of the nature and effects of turbulence. The focus of this thesis is the development of appropriate numerical methods for the computer simulation of turbulent flows. Many of the existing approaches to turbulence utilize analogies from kinetic theory. Degond & Lemou (J. Math. Fluid Mech., 4, 257-284, 2002) derived a k-✏ type turbulence model completely from kinetic theoretic framework. In the first part of this thesis, a numerical method is developed for the computer simulation based on this model. The Boltzmann equation used in the model has an isotropic, relaxation collision operator. The relaxation time in the collision operator depends on the microscopic turbulent energy, making it difficult to construct an efficient numerical scheme. In order to achieve the desired numerical efficiency, an appropriate change of frame is applied. This introduces a stiff relaxation source term in the equations and the concept of asymptotic preserving schemes is then applied to tackle the stiffness. Some simple numerical tests are introduced to validate the new scheme. In the second part of this thesis, alternative approaches are sought for more efficient numerical techniques. The Lattice Boltzmann Relaxation Scheme (LBRS) is a novel method developed recently by Rohan Deshmukh and S.V. Raghuram Rao for simulating compressible flows. Two different approaches for the construction of implicit sub grid scale -like models as Implicit Large Eddy Simulation (ILES) methods, based on LBRS, are proposed and are tested for Burgers turbulence, or Burgulence. The test cases are solved over a largely varying Reynolds number, demonstrating the efficiency of this new ILES-LBRS approach. In the third part of the thesis, as an approach towards the extension of ILES-LBRS to incompressible flows, an artificial compressibility model of LBRS is proposed. The modified framework, LBRS-ACM is then tested for standard viscous incompressible flow test cases.

In dieser Dissertation wird das kompressible, nicht-hydrostatische und dreidimensionale Modell All Scale Atmospheric Model (ASAM) für Grobstruktur- bzw. Large-Eddy-Simulationen (LES) angewendet, um lokale Inseleffekte in der karibischen Passatwindzone zu untersuchen. Da das Modell bis dato noch keine Anwendung im Bereich von LES feuchter atmosphärischer Grenzschichten und heterogener Oberflächen fand, wurden einige Bestandteile zum Modellcode hinzugefügt oder überarbeitet. Ein Hauptaugenmerk liegt dabei auf das Einbeziehen orographischer Strukturen mittels angeschnittener Zellen (engl. cut cells). Sowohl die räumliche und zeitliche Diskretisierung der Modellgleichungen als auch die nötigen physikalischen Parameterisierungen werden in einer umfassenden Modellbeschreibung zusammengefasst. Die Robustheit und Stabilität der Modellformulierung wird durch eine Reihe von Simulationen idealisierter Testfälle bestätigt. Large-Eddy-Simulationen werden für das Gebiet der Karibikinsel Barbados zur Untersuchung von Inseleffekten bezüglich Grenzschichtmodifikation, Wolkenbildung und vertikaler Durchmischung von Aerosolen durchgeführt. Durch das Vorhandensein einer topographisch strukturierten Inseloberfläche in der Mitte des Modellgebietes muss das Modellsetup offene seitliche Randbedingungen beinhalten. Damit das einströmende Windfeld konsistent mit der Dynamik einer turbulenten, marinen Grenzschicht ist, wird eine neue Methode implementiert und angewendet, welche auf Störungen des potentiellen Temperaturfeldes mittels finiter Amplituden basiert. Beobachtungen aus der SALTRACE-Messkampagne werden benutzt, um die Modellläufe anzutreiben. Die Ergebnisse einiger Sensitivitätstests zeigen Probleme der Modellierung im Bereich der \"Terra incognita\" auf. Dabei handelt es sich um die Modellierung auf räumlichen Skalen, welche zwischen denen von LES und wolkenauflösenden Modellen liegen. Außerdem werden Auswirkungen von entweder turbulent oder laminar anströmenden Windfeldern auf die Simulationsergebnisse untersucht. Besonders die Wolkeneigenschaften im Lee von Barbados werden in diesen Simulationen merklich beeinflusst. Ergebnisse einer weiteren Simulation mit einer sehr starken Passatinversion bringt deren Einfluss auf die Dicke und Höhe der simulierten Wolkenschichten zum Vorschein. Die Veränderung von Saharastaubschichten, welche Barbados über weiträumigen Transport über den Atlantik erreichen, wird analysiert. Die Auswirkungen beinhalten sowohl eine Ausdünnung und ein Absinken dieser Schichten als auch turbulenter Transport in Richtung Erdoberfläche. Die genaue Position der beeinflussten Schichten und die Stärke des turbulenten Mischens werden hauptsächlich von der atmosphärischen Schichtung, der Inversionsstärke und Windscherung gesteuert. Vergleiche zwischen den LES-Modellergebnissen und Daten aus Doppler-Windlidarmessungen zeigen gute Übereinstimmungen in der Formierung der konvektiven Strukturen tagsüber und des Vertikalwindfeldes. / In this thesis, the fully compressible, three-dimensional, nonhydrostatic atmospheric model called All Scale Atmospheric Model (ASAM) is utilized for large eddy simulations (LES) to investigate local island effects at the Caribbean. Since the model has not been applied to LES for moist boundary layers and heterogeneous surfaces so far, several parts are added to the model code or reworked. A special focus lies on the inclusion of orographical structures via the cut cell method. Spatial and temporal discretization as well as necessary physical parameterizations are summarized in a thorough model description. The robustness of the model formulation is confirmed by a set of idealized test case simulations. Large eddy simulations are performed for the area of the Caribbean island Barbados to investigate island effects on boundary layer modification, cloud generation and vertical mixing of aerosols. Due to the presence of a topographically structured island surface in the domain center, the model setup has to be designed with open lateral boundaries. In order to generate inflow turbulence consistent with the upstream marine boundary layer forcing, the newly developed cell perturbation method based on finite amplitude perturbations is applied. Observations from the SALTRACE field campaign are used to initialize the model runs. Several numerical sensitivity tests are carried out to demonstrate the problems related to \"gray zone modeling\" beyond LES scales or when the turbulent marine boundary layer flow is replaced by laminar winds. Especially cloud properties west of Barbados (downwind) are markedly affected in these simulations. Results of an additional simulation with a strong trade-wind inversion reveal its effect on cloud layer depth and height. The modification of Saharan dust layers reaching Barbados via long-range transport over the North Atlantic is analyzed. Effects of layer thinning, subsidence and turbulent downward transport near the layer bottom become apparent. The position of these layers and strength of downward mixing is found to be mainly controlled atmospheric stability, inversion strength and wind shear. Comparisons of LES model output with wind lidar data show similarities in the formation of the daytime convective plume and the vertical wind structure.

Transportation is the main source of environmental noise in Europe, with an estimated 125 million people affected by excessive noise levels from road traffic, causing a burden of noise related diseases and having a substantial economic impact on society. In order to reduce exposure to high levels of traffic noise, two approaches are the topic of extensive research: preventing sound from propagating from roads and railways using for example noise barriers, and reducing the sources of noise themselves. The second solution, which addresses directly the cause of the problem, requires improved design methods, with a more systematic resort to multi-functional design. Addressing cross-functions simultaneously reduces the number of design iterations and the high cost of prototyping. The work presented in this thesis aims at developing methods that can be used to design quieter vehicle concepts within a multi-functional approach, and is articulated around two main axis of research, aerodynamic sound generation and sound propagation. The first axis aims at performing an aeroacoustic analysis to predict aerodynamic sound sources. A hybrid method is used on the example of a type of submerged air inlet called a NACA duct, where the near-field flow is solved through detached eddy simulation (DES) and where the far-field acoustics is computed using the Ffowcs Williams and Hawkings integral. Results for the flow for various operating conditions are presented and validated against experimental data from the literature, with very good agreement. Far-field acoustic results are shown, exhibiting levels and components that are strongly dependent on the operating conditions. This analysis gives a framework for future aeroacoustic analysis in the project, and sets the path for the development of air inlets with improved aerodynamic and aeroacoustic characteristics. The second axis focuses on the propagation of sound from a given source, moving in an urban environment. An approximate boundary method is presented, which relies on the Kirchhoff approximation applied to the Kirchhoff-Helmholtz integral equation. Using this approximation speeds up the computational time compared to using a regular boundary element method. The resulting expression is extended to account for multiple scattering through consecutive updates of the surface pressures, and for moving sources through the introduction of a retarded time and of a Doppler shift. Validation tests for this method are presented, from simple scatterers to a more realistic configuration, showing good agreement with analytical, experimental and simulated work. / Fordon är den främsta källan till bullerexponering i Europa med uppskattningsvis 125 miljoner människor som är utsatta för höga ljudnivåer från vägtrafik, vilket kan orsaka bullerrelaterade häsloproblem samt har en betydande ekonomisk effekt på samhället. För att minska exponeringen för höga ljudnivåer från fordon, finns det två angreppssätt som båda idag är ämne för omfattande forskning: att förhindra ljudutbredning från vägar och järnvägar (till exempel med hjälp av bullerskydd), samt att minska ljudnivån från olika bullerkällor. Den sistnämnda, som direkt riktar sig till problemets orsak, kräver förbättrade designmetoder med mer systematisk användning av multifunktionell design. Att hantera flera funktioner hos fordonet samtidigt minskar antalet designiterationer och den höga kostnaden för prototyper. Arbetet som presenteras i denna avhandling syftar till att utveckla metoder som kan användas för att utforma tystare fordonskoncept inom ramen för en multifunktionell strategi och fokuserar på två spår i forskningen: aerodynamisk ljudalstring och ljudutbredning från rörliga källor. Det första spåret i forskningen syftar till att utföra en aeroakustisk undersökning för att modellera aerodynamiska ljudkällor. En hybridmetod tillämpas på ett typ av nedsänkt luftintag, kallat NACA-intag, där källområdet i strömningen löses genom detached eddy simulation (DES) och akustiken i fjärrfältet beräknas enligt Ffowcs Williams och Hawkings integral. Resultat för strömningen för olika driftförhållanden presenteras och valideras mot experimentella data från litteraturen, med mycket god överensstämmelse. Resultat för det akustika fjärrfältet visas, vilket uppvisar nivåer och komponenter som är starkt beroende av driftförhållandena. Denna analys ger en ram för kommande analyser av aeroakustik inom projektet och visar vägen för utvecklingen av luftintag med förbättrade aerodynamiska och aeroakustika egenskaper. Det andra spåret i forskningsprojektet är inriktat på ljudets utbredning från en given källa som rör sig i en urban miljö. En approximativ randvärdesmetod presenteras som bygger på Kirchhoff approximation tillämpad på Kirchhoff-Helmholtz integralekvation. Med hjälp av denna approximation minskas beräkningstiden jämfort med vanlig boundary element method (BEM). Modellen utvecklas sedan för att kunna hantera flera reflektioner genom att det akustiska trycket på ytorna uppdateras för varje reflektion samt för att kunna hantera rörliga källor genom att introducera tidsfördröjningar och Dopplerförskjutning. Validering för denna modell presenteras, från enkla spridare till en mer realistisk urban konfiguration, som visar god överensstämmelse med analytiskt, experimentellt och simulerat data. / <p>QC 20151002</p>

La conception de chambres de combustion aéronautiques requiert un compromis entre les différents phénomènes physiques présents, comme les interactions entre la flamme et la turbulence, les pertes thermiques, la dynamique de flamme ou l'évaporation du carburant et son mélange. De nombreux outils numériques existent dans la littérature pour prédire ce genre d'écoulements réactifs turbulents. Les modèles de turbulence instationnaires, par exemple LES (Large Eddy Simulation), sont un excellent compromis pour la prédiction du mélange dans des configurations réalistes. L'approche de chimie tabulée représente un équilibre attrayant entre coût de calcul et précision pour la prédiction de structure de flamme. Dans cette thèse, des modèles de turbulence avancés et de chimie tabulée sont appliqués à des configurations complexes afin d'évaluer leur capacité à prédire la structure de flammes turbulentes. La prédiction de la FDF (Flame Describing Function) par le modèle F-TACLES (Filtered TAbulated Chemistry for Large Eddy Simulations) est comparé à des données expérimentales pour une flamme swirlée, prémélangée et non-adiabatique. La FDF est bien prédite pour une large plage de fréquences et deux niveaux de fluctuations de vitesse. L'origine des différences est analysée. La première application du modèle F-TACLES à un brûleur diphasique est proposée. Le brûleur choisi est la flamme jet diphasique KIAI, récemment étudié au CORIA. Une comparaison détaillée avec l'expérience est faite et montre que F-TACLES est capable de prédire la bonne forme de flamme. Le modèle ZDES (Zonal Detached Eddy Simulation) est étudié dans la configuration TLC, un injecteur aéronautique réaliste. En non-réactif, la ZDES est validée par rapport aux mesures de vitesse expérimentales et comparée à des résultats de LES. En conditions réactives, la prédiction des profils de température dans la chambre de combustion est grandement améliorée en ZDES. / The design of aeronautical combustion chambers requires a precise balance between the different physical phenomena involved, such as flame-turbulence interaction, heat losses, flame dynamics or fuel evaporation and mixing. Numerous numerical tools exist in the literature to predict these kinds of turbulent reacting flows. The unsteady turbulence models, for example LES (Large Eddy Simulation), represent an excellent compromise for the prediction of the mixing in realistic configurations. The tabulated chemistry approach is an attractive trade-off between computation cost and accuracy for predicting the structure of flames. In this thesis, advanced turbulence and tabulated chemistry models are applied to complex configurations in order to assess their ability to predict the structure of turbulent flames. The prediction of the FDF (Flame Describing Function) by the F-TACLES (Filtered TAbulated Chemistry for Large Eddy Simulations) model is compared to experimental data for a non-adiabatic premixed swirled flame. The FDF is well predicted for a wide range of frequencies and two velocity fluctuation levels. The origin of the discrepancies is analyzed. The first application of the F-TACLES model in a two-phase burner is proposed. The chosen burner is the KIAI spray jet flame, recently studied at CORIA. A detailed comparison with the experiments is performed and shows that F-TACLES is able to predict the correct flame shape. The ZDES (Zonal Detached Eddy Simulation) model is studied in a realistic aeronautical injector, the TLC configuration. In cold conditions, the ZDES is validated against velocity measurements and compared to LES results. In reacting conditions, the prediction of temperature profiles in the combustion chamber is greatly improved in the ZDES.

In turbomachines, rotors and stators differ by the rotation of the former. Hence, half of each stage is directly influenced by rotation effects. The influence of rotation on the flow structure and its impact on the performance is studied through wall-resolving large Eddy simulations of a rotor with large relative tip gap size. The simulations are performed in a rotating frame with rotation accounted for through a Coriolis force term. In a first step, experimental results are used to provide validation. The main part of the study is the comparison of the results from two simulations, one representing the rotating configuration and one with the Coriolis force removed, without any other change. This setup allows a very clean assessment of the influence of rotation. The turbulence-resolving approach ensures that the turbulent flow features are well represented. The results show a significant impact of rotation on the secondary flow. In the tip region, the tip leakage vortex is enlarged and destabilized. Inside the tip gap, the flow is altered as well, with uniformization in the rotating case. At the blade midspan, no significant effects are observed on the suction side, while an earlier transition to turbulence is found on the pressure side. Near the hub, rotation effects are shown to reduce the corner separation significantly.

In the past decades, stricter legislation has been imposed to improve fuel economy and to reduce tail-end emissions of automotive vehicles worldwide. One of the important and effective technologies adopted by the automobile manufacturers to fulfill legislation requirements is the turbocharger technology. As unavoidable large temperature gradients exists in an automotive turbocharger, heat transfer is prominent. However, the effects of heat loss on the turbocharger turbine performance is unclear, i.e. there is no consensus about its effects among researchers. Therefore, the objective of the licentiate thesis is to investigate the effects of heat transfer on an automotive turbocharger radial turbine performance. Furthermore, the thesis also aims to quantify the heat transfer related losses in a turbocharger turbine. Both gas stand (continuous flow) and engine-like (pulsating flow) conditions are considered. By using Detached Eddy Simulation (DES), the flow field of the targeted turbocharger turbine is computed under adiabatic and non-adiabatic conditions. Energy balance and exergy concept are then applied to the simulations data to study the effects of heat loss on performance and to quantify the heat transfer related losses. The main findings of the licentiate thesis are 1) Pressure ratio drop in turbine is less sensitive to heat loss as compared with turbine power. Hence there is a risk of making wrong conclusions about the heat transfer effects on the turbine performance by just comparing the measured pressure ratio under adiabatic and non-adiabatic scenarios; 2) It is possible to quantify heat transfer related losses in a turbocharger turbine. This quantification allows understanding on how well the turbine system utilizes the available energy, and assisting identification of the system component that is sensitive to heat transfer; 3) Heat loss has insignificant effect on turbine power under the investigated engine-like pulsating flow condition; and 4) Even under unavoidable non-adiabatic conditions, much of the exergy discharged out to the environment and more effort could be done to recover the wasted exergy as useful turbine work in the current turbine system. The outcomes of the licentiate thesis naturally lead to the main focus of future work, i.e. exploring different exhaust valve strategies to minimize losses and to optimize flow exergy extraction as useful turbine work for better exhaust gas exergy utilization. / Under de senaste decennierna har allt strängare lagstiftning införts för att förbättra bränsleekonomin och minska avgasutsläppen från motorfordon världen över. En av de viktigaste och mest effektiva tekniker som införts av biltillverkarna för att kunna uppfylla lagkraven är turboladdartekniken. Eftersom stora temperaturgradienter existerar i en fordonsturboladdare, spelar värmeöverföring en framträdande roll. Emellertid är effekterna av värmeförluster på turboturbinprestanda oklar, dvs det finns ingen konsensus bland forskare om dess effekter. Syftet med denna licentiatavhandling är därför att undersöka effekterna av värmeöverföring på prestanda för radialturbinen i en fordonsturboladdare. Vidare syftar avhandlingen till att kvantifiera värmeöverföringsrelaterade förluster i en turboladdares turbin. Både fall med kontinuerligt gas flöde och motorliknande, pulserande flöde beaktas. Strömningsfältet i den utvalda turboladdarens turbin beräknas med en metod kallad Detached Eddy Simulation (DES) under adiabatiska och icke adiabatiska förhållanden. Energi- och exergibalanser för simuleringsresultaten analyseras sedan för att studera effekterna av värmeförluster på prestanda och kvantifiera värmeöverföringsrelaterade förluster. De viktigaste resultaten av licentiatuppsatsen är 1) Tryckförhållandet över turbinen är mindre känsligt för värmeförluster jämfört med turbineffekten. Därmed finns det en risk för att felaktiga slutsatser dras beträffande effekterna av värmeöverföring på turbinprestanda genom att enbart jämföra det uppmätta tryckförhållandet under adiabatiska och icke adiabatiska förhållanden; 2) Det är möjligt att kvantifiera värmeöverföringsrelaterade förluster i en turboladdares turbin. Denna kvantifiering ger förståelse för hur väl turbinsystemet utnyttjar den tillgängliga energin, och bistår med identifiering av systemkomponenter som är känsliga för värmeöverföring; 3) Värmeförluster har en obetydlig inverkan på turbineffekten för det undersökta motorliknande, pulserande flödesförhållandet; och 4) Under oundvikliga, icke-adiabatiska förhållanden, släpps även en stor del av exergin ut till omgivningen och det finns utrymme för förbättringar gällande exergiutnyttjandet i det aktuella turbinsystemet. Baserat på resultaten av licentiatavhandlingen kommer det fortsatta arbetet att fokusera på att utforska olika avgasventilstrategier för att minimera förluster och optimera omvandling av flödesexergi till användbart turbinarbete för bättre avgasexergiutnyttjande. / <p>QC 20161213</p> / KTH CCGEx HOTSIDE project