This thesis is a collaboration between Siemens Industrial Turbomachinery(SIT) and Royal Institute of Technology(KTH). It is aimed to study and compare the outputs of two different computational approaches in axial gas turbine design procedure with the data obtained from experimental work on a test turbine. The main focus during this research is to extend the available test databank and to further understand and investigate the turbine stage efficiency, mass flow parameters and reaction degree under different working conditions. Meanwhile the concept and effect of different loss mechanisms and models will be briefly studied.  The experimental part was performed at Heat and Power  Technology department on a single stage test turbine in its full admission mode. Three different pressure ratios were tested. For the medium pressure ratio a constant temperature anemometry (CTA) method was deployed in two cases, with and without turbulence grid, to determine the effect of free-stream turbulence intensity on the investigated parameters. During the test campaign the raw gathered data was processed with online tools and also they served as boundary condition for the computational codes later.  The computational scope includes a one-dimensional design approach known as mean-line calculation and also a two-dimensional method known as throughflow calculation. An in-house SIT software, CATO, generated the stage geometry (vane, blade and the channel) and then two other internal computational codes, MAC1 and BETA2, were employed for the one-dimensional and two-dimensional computations respectively. It was observed that to obtain more accurate mass flow predictions a certain level of channel blockage should be implemented to represent the boundary layer development and secondary flow which is typically around 2%. The codes are also equipped with two options to predict the friction loss: One is a more empirical correlation named as the Old approach in SIT manuals and the other works based on allocation of boundary layer transition point, named as BL in the present thesis. Simulations were done by use of both approaches and it turned out that the latter works more accurately if it is provided with appropriate transition point and blockage estimation.  The measured data also suggests the idea that the transition point of the vane and blade is not affected by a change in turbulence intensity at least up to 6% in the tested Reynolds numbers, . Amongst different solutions the one which used BL approach and constant transition point (while the turbulence intensity changed) managed to predict this behavior. Also it was investigated and revealed that the codes inherently predict poor results in off-design loadings which is mainly due to positive incidence angle in addition to high spanwise gradient of the flow parameters.

The global Meridional Overturning Circulation (MOC) plays a significant role in the Earth\'s climate system by redistributing all over the world the excess heat gained by Earth in low latitudes. In its superficial branch, warm waters are exchanged throughout the world\'s ocean basins. The Indonesian Throughflow (ITF) and the Agulhas Leakage (AL) are the main processes responsible, respectively, for importing Pacific Ocean waters into the Indian Ocean, and for exporting Indian Ocean waters into the Atlantic Ocean. Recently, changes in both systems have been reported and can be related to global warming consequences, processes of air-sea interactions and variabilities in the ocean circulation and wind patterns. In the present work, output of a high-resolution, global implementation of HYCOM (Hybrid Coordinate Ocean Model) from different runs were used, aiming at a study of the structure and variability of the ITF, and to evaluate the use of a numerical tool for tracking virtual Lagrangian particles to correlate circulation patterns of the ITF and the AL. For the ITF, analysis of the models\' output provided a mean volume transport in the upper 700 m depth of about 13 Sv, what is in the range of values reported by observations and other numerical simulations in the region. The seasonal variability was found to be related to the monsoons wind regimes, and the ITF\'s response to the El Niño-Southern Oscillation (ENSO) was evaluated. During five La Niña events, the mean volume transport was of approximately 16 Sv, and for also five El Niño events, of approximately 12 Sv. Results show an abrupt increase in the heat transport between 2002 and 2012, what could be related to changes in the heat content within the Indian Ocean for the same period. Heat transport anomalies were analyzed in the last years of the time series and present a clear correlation with Nino3.4 index, denoting a strong response of the ITF to the 2014/16 El Niño. Numerical test-experiments simulating Lagrangian particles have been performed, to identify and quantify water masses\' origins compounding the ITF and to correlate variabilities signals of ITF in the Indian Ocean\'s basin circulation and in the Agulhas Leakage. / A Circulação de Revolvimento Meridional do oceano desempenha um papel importante no sistema climático da Terra, através da redistribuição do excesso de calor ganho pelo planeta em baixas latitudes. No seu ramo superficial, massas de águas quentes são carregadas entre as diferentes bacias oceânicas no mundo. O fluxo que ocorre através dos estreitos dos mares da Indonésia (ITF, Indonesian Throughflow), e o Vazamento das Agulhas (VA) são dois importantes processos responsáveis, respectivamente, por importar águas do Pacífico para o Oceano Índico, e por exportar águas do Índico para o Oceano Atlântico. Recentemente, mudanças em ambos sistemas têm sido reportados e podem estar relacionados a consequências do aquecimento global, a processos de interação ar-mar e a variabilidades da circulação oceânica e de padrões de vento. No presente trabalho foram usadas saídas de diferentes rodadas usando uma implementação global em alta resolução do HYCOM (Hybrid Coordinate Ocean Model), com o objetivo de estudar a estrutura e variabilidade do ITF e avaliar o uso de uma ferramenta numérica para rastrear virtualmente a trajetória de partículas Lagrangianas e correlacionar padrões de circulação do ITF e do VA. Para o ITF, análises dos resultados dos modelos forneceram um valor de transporte de volume de ≈13 Sv para os primeiros 700 m de profundidade, o qual está em acordo com valores obtidos por observações e outras simulações numéricas. A variabilidade sazonal foi demonstrada estar relacionada aos regimes de vento de monções, e a resposta do ITF para o El Niño-Oscilação Sul (ENOS) foi avaliada. Durante cinco eventos de La Niña o transporte de volume médio foi de ≈16 Sv, e para cinco eventos de El Niño, em ≈12 Sv. Os resultados mostram um aumento abrupto no transporte de calor entre 2002 e 2012, o qual pode estar relacionado a mudanças na quantidade de calor dentro do Oceano Índico para o mesmo período. Anomalias no transporte de calor foram analisadas para os últimos anos da mesma série temporal e também apresentou clara correlação com o índice Nino3.4, configurando uma forte resposta do ITF para o El Niño de 2014/16. Experimentos numéricos simulando partículas Lagrangianas foram implementados, com o objetivo de identificar origens de massas de águas que compõem o ITF e correlacionar sinais de variabilidade do ITF na bacia de circulação do Índico e do Vazamento das Agulhas.

No description available.

Thesis (MScEng)--Stellenbosch University, 2006. / ENGLISH ABSTRACT: The Stellenbosch University Compressor Code (SUCC) has been developed for the purpose of predicting the performance of axial flow compressors by means of axisymmetric inviscid throughflow methods with boundary layer blockage and empirical blade row loss models. This thesis describes the process of the implementation and verification of a number of stall prediction criteria in the SUCC. In addition, it was considered desirable to determine how certain factors influence the accuracy of the stall prediction criteria, namely the nature of the computational grid, the choice of throughflow method used, and the use of a boundary layer blockage model and a radial mixing model. The stall prediction criteria implemented were the di®usion factor limit criterion, de Haller's criterion, Aungier's blade row criterion, Aungier's boundary layer separation criterion, Dunham's, Aungier's and the static-to-static stability criteria. The compressors used as test cases were the Rofanco 3-stage low speed compressor, the NACA 10-stage subsonic compressor, and the NACA 5-stage and 8-stage transonic compressors. Accurate boundary layer blockage modelling was found to be of great importance in the prediction of the onset of stall, and that the matrix throughflow Method provided slightly better accuracy than the streamline curvature method as implemented in the SUCC by the author. The ideal computational grid was found to have many streamlines and a small number of quasi-orthogonals which do not occur inside blade rows. Radial mixing modelling improved the stability of both the matrix throughflow and streamline curvature methods without significantly affecting the accuracy of the stall prediction criteria. De Haller's criterion was over-conservative in estimating the stall line for transonic conditions, but more useful in subsonic conditions. Aungier's blade row criterion provided accurate results on all but the Rofanco compressor. The diffusion factor criterion provided over- optimistic predictions on all machines, but was less inaccurate than de Haller's criterion on the NACA 5-stage transsonic machine near design conditions. The stability methods performed uniformly and equally badly, supporting the claims of other researchers that they are of limited usefulness with throughflow simulations. Aungier's boundary layer separation method failed to predict stall entirely, although this could reflect a shortcoming of the boundary layer blockage model. / AFRIKAANSE OPSOMMING: Die Stellenbosch University Compressor Code (SUCC) is ontwikkel om die prestasie van aksiaalvloei kompressors te voorspel met behulp van aksisimmetriese nie-viskeuse deurvloeimetodes met grenslaagblokkasie en empiriese modelle vir die verliese binne lemrye. Hierdie tesis beskryf die proses waarmee sekere staakvoorspellingsmetodes in die SUCC geïmplementeer en geverifieer is. Dit was ook nodig om die effek van sekere faktore, naamlik die vorm van die berekeningsrooster, die keuse van deurvloeimetode en die gebruik van `n grenslaagblokkasiemodel en radiale vloeivermengingsmodel op die akuraatheid van die staakvoorspellingsmetodes te bepaal. Die staakvoorspellingsmetodes wat geïmplementeer is, is die diffusie faktor beperking metode, de Haller se metode, Aungier se lemrymetode, Aungier se grenslaagmetode en die Dunham, Aungier en die statiese-tot-statiese stabiliteitsmetodes. Die kompressors wat gebruik is om die metodes te toets is die Rofanco 3-stadium lae-spoed kompressor, die NACA 10-stadium subsoniese kompressor en die NACA 5- en 8-stadium transsoniese kompressors. Daar is vasgestel dat akkurate grenslaagblokkasie modelle van groot belang was om `n akkurate aanduiding van die begin van staking te voorspel, en dat, vir die SUCC, die Matriks Deurvloei Metode oor die algemeen 'n bietjie meer akkuraat as die Stroomlyn Kromming Metode is. Daar is ook vasgestel dat die beste berekeningsrooster een is wat baie stroomlyne, en die kleinste moontlike getal quasi-ortogonale het, wat nie binne lemrye geplaas mag word nie. Die numeriese stabiliteit van beide die Matriks Deurvloei en die Stroomlyn Kromming Metode verbeter deur gebruik te maak van radiale vloeivermengingsmodelle, sonder om die akkuraatheid van voorspellings te benadeel. De Haller se metode was oorkonserwatief waar dit gebruik is om die staak-lyn vir transsoniese vloei toestande, maar meer nuttig in die subsoniese vloei gebied. Aungier se lemrymetode het akkurate resultate gelewer vir alle kompressors getoets, behalwe die Rofanco. Die diffusie faktor metode was oor die algemeen minder akuraat as Aungier se metode, maar meer akkuraat as de Haller se metode vir transsoniese toestande. Die stabiliteitsmetodes het almal ewe swak gevaar. Dit stem ooreen met die bevindings van vorige navorsing, wat bewys het dat hierdie metodes nie toepaslik is vir simulasies wat deurvloeimetodes gebruik nie. Aungier se grenslaagmetode het ook baie swak gevaar. Waarskynlik is dit as gevolg van tekortkomings in die grenslaagblokkasiemodel.

The transition of the European energy grid to renewable energy sources is increasing the demand for back-up capacity with high flexibility. Current fossil fuel plants are continuously being forced into part load operation, where they are limited by pollution regulations that dictate their minimum environmental load, MEL. The power plants need to shut down when they no longer can comply to pollution regulations, but shutting down means that they can't act as quick back-up for the energy grid. Thus the EU project Turbo-Reflex aims to retrofit existing power plants in order to improve MEL by extending it to lower loads and, by doing so, meeting some of the back-up capacity that is needed. One method of improving MEL in a gas turbine power plants is reducing the mass flow from the compressor to the combustor. This study aims to investigate the stability and performance changes in a compressor as a function of intermediate mass extraction through bleeding lines. The study was made using a 2D throughflow model of a 15 stage axial compressor. Three different bleeding lines, positioned along the length of the compressor, were used for flow reduction. A design of experiments was made to get a structured data collection, combining different configurations of bleeding levels through the three lines, with up to 20% flow reduction. The influence of lowering the ambient temperature was also studied. Results detail the aerodynamic influence of intermediate mass extraction. The loading at the last stage increases with flow reduction, as evaluated by the diffusion factor, and stator 15 becomes the highest aerodynamically loaded position in the compressor. The increased loading is significantly dependent on the bleeding configuration, where upstream extraction is advantageous. The compressor power requirement has the same behavior, where extracting upstream has a 10% advantage. However, bleeding reduces efficiency, and in this regard it is better to use a bleed line further downstream. This combines into a trade off between these three parameters that needs to be made by the operator. Lowering the ambient temperature changes the interplay between these parameters. These research's results are part of the TURBO-REFLEX project, which has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No. 764545.

Experiments with a coupled atmosphere-ocean-sea ice model using idealized topographies were run to investigate aspects of the role that the lateral ocean constraints play in the climate. The experiments consider an idealized planet covered with a constant deep ocean, where one-grid-wide land barriers were gradually added. The series of experiments allowed the investigation of many aspects of the coupled system equilibrium and variability, ending with an evaluation of the effects of the Indonesian Throughflow. Rather than to investigate the throughflow\'s impacts in modern climate, which has been largely explored in numerical experiments in the past decades, the throughflow is investigated in an alternative climate, argued as a possible scenario during ice-age periods. It was found that the change in the hemispheric water source of the throughflow affects many aspects of its impact as it is known for modern climate. In summary, the throughflow acts within the inter-basin seesaw in the sense to restore the previous phase of the inter-basin seesaw. / Experimentos com um modelo acoplado oceano-continente-atmosfera-gelo marinho e topografias idealizadas foram empregados para investigar os impactos que contornos laterais nos oceanos desempenham no clima. Os experimentos consideram um planeta idealizado, coberto por um oceano de profundidade constante, onde barreiras com um ponto de grade de espessura foram gradualmente adicionadas. Esta série de experimentos permitiram investigar vários aspectos do sistema acoplado em termos de seu equilíbrio e variabilidade, finalizando com a análise dos efeitos devidos ao Fluxo da Indonésia. Ao invés de investigar os impactos que este fluxo tem sobre o clima atual, o que tem sido bastante explorado em experimentos numéricos nas últimas décadas, a investigação é feita num clima alternativo, que configura um possível cenário durante períodos glaciais. Foi encontrado que a mudança na origem das águas que compõem o Fluxo da Indonésia altera em vários aspectos seus impactos como são conhecidos no clima atual. Em suma, o Fluxo da Indonésia atua dentro de um mecanismo de gangorra inter-hemisférica na circulação termoalina no sentido de reestabelecer a fase anterior desse mecanismo tipo gangorra.

Experiments with a coupled atmosphere-ocean-sea ice model using idealized topographies were run to investigate aspects of the role that the lateral ocean constraints play in the climate. The experiments consider an idealized planet covered with a constant deep ocean, where one-grid-wide land barriers were gradually added. The series of experiments allowed the investigation of many aspects of the coupled system equilibrium and variability, ending with an evaluation of the effects of the Indonesian Throughflow. Rather than to investigate the throughflow\'s impacts in modern climate, which has been largely explored in numerical experiments in the past decades, the throughflow is investigated in an alternative climate, argued as a possible scenario during ice-age periods. It was found that the change in the hemispheric water source of the throughflow affects many aspects of its impact as it is known for modern climate. In summary, the throughflow acts within the inter-basin seesaw in the sense to restore the previous phase of the inter-basin seesaw. / Experimentos com um modelo acoplado oceano-continente-atmosfera-gelo marinho e topografias idealizadas foram empregados para investigar os impactos que contornos laterais nos oceanos desempenham no clima. Os experimentos consideram um planeta idealizado, coberto por um oceano de profundidade constante, onde barreiras com um ponto de grade de espessura foram gradualmente adicionadas. Esta série de experimentos permitiram investigar vários aspectos do sistema acoplado em termos de seu equilíbrio e variabilidade, finalizando com a análise dos efeitos devidos ao Fluxo da Indonésia. Ao invés de investigar os impactos que este fluxo tem sobre o clima atual, o que tem sido bastante explorado em experimentos numéricos nas últimas décadas, a investigação é feita num clima alternativo, que configura um possível cenário durante períodos glaciais. Foi encontrado que a mudança na origem das águas que compõem o Fluxo da Indonésia altera em vários aspectos seus impactos como são conhecidos no clima atual. Em suma, o Fluxo da Indonésia atua dentro de um mecanismo de gangorra inter-hemisférica na circulação termoalina no sentido de reestabelecer a fase anterior desse mecanismo tipo gangorra.

Lors de sa détente dans une turbine, la vapeur subit une chute d’enthalpie qui entraîne sa condensation spontanée sous forme d’un nuage de gouttelettes submicroniques. Ces gouttes vont se déposer sur les aubes aval et y former un film d’eau. Ce dernier est arraché sous l’effet de l’écoulement de vapeur environnant ce qui crée des gouttes de quelques dizaines de microns qui peuvent se redéposer sur les aubes aval. Ces phénomènes sont à l’origine de pertes, généralement regroupées sous le terme générique de ”pertes par humidité”, estimées grâce à la loi de Baumann. Le but de cette thèse est de mettre en place dans un code méridien des modèles permettant la prise en compte des phénomènes de condensation, de déposition et d’écoulement des films liquides afin de pouvoir estimer les pertes liées à chacun d’entre eux. Dans cette optique un modèle diphasique homogène permettant d’avoir accès à la fraction massique de liquide et au nombre de gouttes est implanté dans le code méridien. Ce modèle est validé sur un cas test expérimental de détente en tuyère et alimente le modèle de déposition. Les contributions de la diffusion, de la turbophorèse, de la thermophorèse, de la gravité et de l’inertie des gouttes à la déposition sont étudiées. Il apparaît nécessaire de prendre en compte la diffusion, la turbophorèse et la déposition inertielle sur les bords d’attaque des aubes. Un modèle permettant d’avoir accès à l’épaisseur et à la vitesse d’un film liquide soumis au cisaillement d’un écoulement environnant, à la force de frottement sur la paroi et aux effets de la rotation est mis en place. Ce modèle est validé par rapport à des résultats expérimentaux d’écoulement de film liquide sur une plaque plane dans des conditions proches de celles rencontrées en turbine à vapeur basse pression. Finalement, un calcul réalisé sur une géométrie réelle de turbine basse pression de 8 étages permet de démontrer l’applicabilité de la méthodologie mise en place sur un cas industriel. Les contributions des phénomènes étudiés aux pertes par humidité sont explicitées. / During the expansion in a turbine, the enthalpy of the steam fall. This fall leads the steam to cross the saturation line and brings about its spontaneous condensation and the appearance of fog droplets. The deposition of these droplets on downstream blades lies at the root of the creation of a liquid film. This film is torn off by steam flow and creates coarse water. These big droplets can impact downstream blades. Each of these phenomena induces some losses which are generally grouped in the ”wetness losses” estimated thanks to Baumann’s rule. The aim of this work is to develop, in a throughflow code, some models which allow to take into account the condensation, deposition and liquid film flow and the losses linked to each of these phenomena. An homogeneous two phases flow model is implemented in the throughflow code. Two transport equations on the mass fraction of liquid and on the droplets number are added to Euler’s equations written for gas phase. This model is validated on an experimental test case of expansion in nozzle and feeds the model of deposition. The influences of diffusion, turbophoresis, thermophoresis, gravity and of inertia of droplets on the deposition are studied. It appears to be necessary to take into account diffusion, turbophoresisand deposition due to inertia on the leading edges of blades. A model which allows to evaluate the thickness and the velocity of a liquid film submitted to aerodynamic shear, friction on blades and rotational effects has been developed. This model is validated on experimental results of a liquid film flow on a flat plate in some conditions representatives of those encountered in low pressure steam turbines. Finally a calculation realised on a real geometry of a 8-stages low pressure steam turbine has demonstrated that the methodology developed during this work can be used on an industrial test case. The contributions of the phenomena studied to wetness losses are evaluated.

In this study, two major internal erosion initiation processes, suffusion and concentrated leak mechanisms, which lead to both defect formation in a dam’s body and its foundation and high throughflow in dams subjected to internal erosion were studied. This understanding has the potential to facilitate numerical modelling and expedite dam safety assessment studies.  The throughflow properties of coarse rockfill material were studied by; analysing filed pump test data, performing extensive laboratory experiments with a large-scale apparatus and numerically simulating the three-dimensional flow through coarse rock materials, replicating the material used in the laboratory experiments. Results from the tests demonstrate that the parameters of the nonlinear momentum equation of the flow depend on the Reynolds number for pore Reynolds numbers lower than 60000.  Numerical studies were also carried out to conduct numerical experiments. By applying a Lagrangian particle tracking method, a model for estimating the lengths of the flow channels in the porous media was developed.  The shear forces exerted on the coarse particles in the porous media were found to be significantly dependent on the inertial forces of the flow. Suffusion and concentrated leak mechanisms were also studied by means of laboratory experiments to develop a theoretical framework for continuum-based numerical modelling. An erosion apparatus was designed and constructed with the capability of applying hydraulic and mechanical loading. Results were then used to develop constitutive laws of the soil erosion as a function of the applied hydromechanical load for both suffusion and concentrated leak mechanisms. Both the initiation and mass removal rate of were found to be dependent on the soil in-situ stresses. A three-dimensional electrical-resistivity-based tomography method was also adopted for the internal erosion apparatus and was found to be successful in visualising the porosity evolution due to suffusion. / <p>QC 20161006</p>

Ce travail avait pour but de reconstituer l'évolution de la température et du δ¹⁸O des eaux de surface et des eaux de la thermocline dans la Warmpool indo-pacifique (IPWP) en combinant la thermométrie Mg / Ca et la mesure des isotopes stables de l'oxygène sur des foraminifères planctoniques de surface et de sub-surface prélevés dans des carottes de sédiments situées dans l'océan Indien tropical oriental. Ce travail a permis de ré-évaluer les effets des différentes méthodes de nettoyage et de la dissolution in situ sur la thermométrie Mg/Ca des foraminifères planctoniques, mettant en évidence la nécessité de corrections différentes suivant les espèces. L’évolution de l’IPWP au cours des 270 000 dernières années a été reconstituée. Les résultats indiquent que le δ¹⁸O des eaux de surface reflètent principalement l'advection latérale plutôt que l'historique des précipitations régionales, et suggèrent que l'hydrologie de surface IPWP est contrôlée par la migration latitudinale de la zone de convergence intertropicale aux échelles de temps orbitales mais aussi en réponse aux événements climatiques abrupts de l'hémisphère nord (eg. événements de Heinrich). Les variations de salinité de surface sont étroitement corrélées aux changements d’export vers l’Atlantique au niveau du Courant des Aiguilles (Sud de l’Afrique). Puis, les changements dans le transport des eaux de la thermocline issues de l’ITF vers l'océan Indien ont été étudiés. Les résultats montrent que le transport était plus faible pendant les glaciations (ie. MIS 6 et 4-2) que pendant les périodes interglaciaires (ie. MIS 7, MIS 5 et Holocène) et exerçaient une influence significative sur les changements de la température de la thermocline dans l'Océan Indien. / This work aimed at reconstructing the late Quaternary evolution of surface and thermocline temperature and ocean surface water δ¹⁸O in the Indo-Pacific Warm Pool by combining Mg/Ca-thermometry and stable oxygen isotope analyses on surface and thermocline-dwelling planktonic foraminifers retrieved from sediment cores in the eastern tropical Indian Ocean. This study allowed to re-evaluate the effects of different cleaning methods and in-situ dissolution on the Mg-thermometry of planktonic foraminifers, evidencing the need for species-dependent corrections. Then, the IPWP evolution over the last 270,000 years has been explored. Results indicate that surface water δ¹⁸O chiefly reflects lateral advection rather than local precipitation history, and suggest that surface IPWP hydrology is controlled by the latitudinal migration of the Intertropical Convergence Zone at orbital timescale as well as during abrupt northern hemisphere climatic events (i.e. Heinrich events). Ocean surface salinity in the IPWP and Agulhas leakage region varied synchronously, implying their teleconnection through oceanic and atmospheric circulation. Moreover, changes in the transport of thermocline water to the Indian Ocean by the Indonesian Throughflow (ITF) have been reconstructed. Results show that thermocline water transport was weaker during glacials (i.e. MIS 6 and 4-2) than during interglacials (MIS 7, MIS 5 and Holocene), and exerted significant influence on Indian Ocean TWT change.