Electricity has been proved to be a crucial factor to achieve an economic and social development in emergent countries and is seen as a necessity to deplete the world’s poverty. As energy resources are getting scarce, a higher implementation of renewable electricity generation, such as hydropower, is a necessity. Hydrokinetic turbines, which use slow flowing water as a source of energy, are to be installed in the Amazonas River in Colombia. The Amazon River has high amount of sediment and flowing objects due to the large quantity of vegetation in the area. This leaves the turbine exposed to a higher degree of erosion on the blades and a higher risk of getting clogged. The efficiency will decrease and the turbine will have an impending risk of getting damaged. By adapting the hydrokinetic turbine for the conditions prevailing in the Amazon basin, the efficiency can be improved and a longer lifetime for the turbine is given. A field study was conducted to attain the velocity and amount of sediment in the Amazon River through measurements. The collected data was analyzed and used as input values during simulations of a turbine model by the Computational Fluid Dynamics program COMSOL. Areas on the turbine exposed to the water with a high velocity, and containing a high concentration of sediment, were examined and proposals for protection were given. Also the necessity and consequences of installing a protective grate in front of the turbine were investigated. The turbine will be exposed to almost a factor of 12 000 higher erosive wear in the Amazon River than in Swedish water as of the higher amount of sediment. The investigation states that areas on the tip of the blade’s rear side and the area close to the rotating center are most exposed to erosion and will be in need of protection in form of a harder surface. A grate will be necessary to provide a longer lifetime for the turbine, but will result in a decreased power output from the turbine by up to 46 %. / Elektricitet har bevisats vara en viktig komponent för en ekonomisk och social utveckling i utvecklingsländer och ses därför som en nödvändighet för att minska fattigdomen i världen. Energikällorna är dock hårt utnyttjade och en högre andel förnyelsebar elektrisk generering, genom bland annat vattenkraft, är en nödvändighet. Hydrokinetiska turbiner, vilka producerar el på långsamt flödande vatten, ska implementeras i Amazonfloden i Colombia. Amazonfloden har en hög andel sediment samt flytande objekt i floden på grund av den höga andel vegetation i området. Detta ger en ökad erosion på bladen samt risk för igentäppning av turbinen efter implementering. En lägre effektivitet samt hög risk för skada på turbinerna erhålls. Genom att adaptera den hydrokinetiska turbinen för förhållanden som råder i Amazonasfloden kan verkningsgraden förbättras och en längre livslängd på turbinen kan erhållas. En fältstudie utfördes där mätningar över vattenhastigheter, mängd sediment samt större objekt i floden genomfördes och analyserades. Data användes sedan som indata vid simuleringar över en uppbyggd modell av turbinen i Computational Fluid Dynamics-programmet COMSOL Multiphysics. Områden på turbinen utsatta för sedimentfullt vatten med en högre hastighet undersöktes och skyddsåtgärder föreslogs. Även behovet av ett skyddande galler framför turbinen granskades. Det visades att turbinen kommer utsättas för nästintill en faktor på 12 000 högre erosion i Amazonasfloden jämfört med i svenska vatten. Undersökningen visar att yttersta delarna av bladets baksida samt ett område nära det roterande centret är i behov av ett extra skydd i form av en hårdare yta. Ett galler kan bli nödvändigt för att uppnå en längre livstid för turbinen, men resulterar i en sänkt elproduktion med upp till 46 %.

In recent years Computational Fluid Dynamics (CFD) has been extensively used in the study of the indoor environment and the thermal comfort conditions for the design of modern buildings, however, there remains the need to thoroughly evaluate the accuracy of the results given by CFD methods. In the present work, numerical investigations of the indoor thermal environment in the atria of two existing buildings and in a simple three-storey atrium building design have been undertaken using CFD techniques. The initial work involved the evaluation of various turbulence models and a radiation model used in CFD simulations for the prediction of the thermal environment in atria of different geometrical configurations in two buildings for which experimental data is available. The airflow patterns and temperature distributions were determined, under both forced and hybrid ventilation conditions and thermal comfort conditions were evaluated. The numerical predictions were compared with the available experimental measurements and, in general, good agreement was obtained between the numerical and experimental results. After the evaluation of the adequacy of available turbulence models and the validation of the accuracy of the CFD model used, a simple full-scale three-storey atrium building was modeled to explore the potential of using buoyancy-driven natural ventilation. The validated CFD model was used to determine the ventilation flow rates, airflow patterns, and temperature distributions in the building. The dynamic effect of the thermal mass of the external walls on the performance of the building was also investigated using transient CFD simulations. Atria with various geometrical configurations were studied in order to investigate the effect of atrium design changes on the air flow and temperature distributions in the simple atrium building considered. A parametric study was carried out to assess the sensitivity of the ventilation performance to the change in various geometric and solar parameters. On the basis of this parametric study, a few changes were carried out in the design of the building to examine their effect on ventilation performance. Finally, the use of night ventilation in the atrium building was explored and it was found that night ventilation can be increased by using hot water circulation in the chimney walls. / Thesis (Ph.D, Mechanical and Materials Engineering) -- Queen's University, 2012-07-22 12:57:00.947

When simulating air flows in an urban environment, for e.g. pollutant dispersion investigations, today's main tool is advanced computational fluid dynamics simulations. These simulations take a lot of time and resources to perform, even for small geometries. In some situations, one would like to be able to run approximate simulations, possibly with large geometries, without such a significant investment. The model described in this thesis is a graph network model which have streets and intersections of an urban environment modeled as connections and nodes in a graph. The model uses a pressured pipe model, based on the Darcy-Weisbach equation, to simulate air flow in the network. Such a model requires only rough measurements of the urban geometry and an estimated Darcy's friction factor, to be able to solve the system. Furthermore, using the same rough geometrical parameters, together with shear velocity, the model solves atmospheric exchange rates of the streets. Intersections play a major role when investigating urban dispersion. The way this model deals with dispersion in any complex intersections, represented by single nodes, is by using wind direction variance together with a distribution parameter based on computational fluid dynamics intersection simulations made in Comsol Multiphysics - also present in this paper. Using the simple model described above, I have simulated urban air flows in a complex urban geometry of a part of Paris. This specific geometry has already been investigated by computational fluid dynamics simulations as well as wind tunnel experiments. By comparing the computational fluid dynamics simulation with my model, I have validated its accuracy. 40% and 45% of all streets reach a relative and absolute error below 25% respectively. Directions of the street velocities have been simulated with approximately 90% accuracy - with distinct error indications. Atmospheric exchange rates of the streets are within an order of magnitude accurate, however, showing a systematic error by overestimating the vast majority of the exchange rates. The model could become even better by covering error sources discussed in the discussion section. Excess theory for simulating each of the above-described flows is presented, which might change the results. For example, slightly altering the modeling of the atmospheric exchange rate might fix the overestimation offset we have seen. Potential error sources could be the varying building heights and the streets angle relative the overlaying wind direction. The pressured pipe simulated flows have shown tendencies to be bad at picking up the effects of high/low buildings following low/high buildings, as well as accurately capture the behavior of streets close to perpendicular to the wind direction. Main streets with plenty of exits have been modeled with intersections at each exit, which results in strong flow variation along a street that should have a flow close to constant. Solving main streets like this separately could improve this behavior drastically.

The purpose of this thesis work was to design a new shape for the BYU Supermileage vehicle in order to improve its fuel efficiency. Computational Fluid Dynamics (CFD) was used to obtain the coefficient of drag (CD) and drag area of the current baseline vehicle at a Reynolds number of 1.6x10^6 and 8.7x10^5. Then a new shape was developed using mesh morphing software. The new shape was imported into the CFD program and the drag figures and airflow plots from the modified design were compared with the baseline vehicle. Scale models of the vehicles were also printed using a 3D printer in order to perform wind tunnel testing. The models were installed in the wind tunnel and the coefficient of drag and drag area were compared at a Reynolds number around 8.7x10^5.It was found from the CFD results that the new vehicle shape (labelled Model C) caused a 10.8% reduction in CD and a 17.4% reduction in drag area under fully laminar flow. Smaller drag reductions were observed when the flow was fully turbulent. From the wind tunnel comparisons, it was found that Model C reduced CD by 5.3% and drag area by 11.4%, while the fully laminar CFD results at Re = 8.7x10^5 showed that Model C reduced CD by 9.8% and drag area by 15.9%. Smaller drag reductions were again observed for fully turbulent flow. Thus in order to improve the aerodynamic performance, the current vehicle shape should be changed to match that of Model C, and laminar flow should be encouraged over as much of the wetted area as possible.

The diploma thesis is focused on calculating the thermal resistance of the line light source and the design of the cooling system with ideal inlet temperature. The partial aim of the work is in cooperation with CAMEA spol. s r. o. to determine the thermal resistances of the individual parts of the device and propose modifications so that the total thermal resistance and the maximum temperature are within the limits given by the cooperating firm. The main objective is to design a cooling system with all safety features and recommended regulation for economical and reliable operation. Analytical calculations, CFD simulations and real-world testing are used to determine the desired results. A reduction by 30% in thermal resistance of the printed circuit board was achieved, the thermal resistance of the aluminum profile with the cooling channel was determined and its hydraulic properties were calculated. The current cooling system designed by CAMEA spol. s r. o. for less powerful diodes was verified for use in a more powerful system, and a new cooling system was designed for efficient and economical operation in a powerful diode system.

Topic of this Master's thesis is CFD simulations of indoor environment in a pharmacy building. CFD simulation have been done for summer and winter season for two scenarios of HVAC system. Results of simulations are visualized and evaluated.

The objective of this diploma thesis is optimization of the current state of internal microclima-te, which was supported by CFD simulations. The solved object is storage hall of electronics of the the company ebm-papst CZ s.r.o.

L'analyse des écoulements au sein des faisceaux d'assemblages constitue un volet important des études des réacteurs à eau pressurisée. Une mauvaise répartition thermique au sein de ces écoulements peut conduire à une crise d'ébullition nuisible à la sûreté du réacteur. De nombreuses études ont montré l'existence de phénomènes de réorganisation de structures aux grandes échelles dans ces écoulements. Cette thèse vise à améliorer notre compréhension de ces phénomènes, l'objectif étant de développer des modélisations aux petits échelles adaptées. Un travail bibliographique a mis en évidence les difficultés rencontrées par les simulations pour reproduire ces phénomènes, ainsi que de nombreux questionnements concernant leur caractère physique. Des simulations 3D ont été réalisées et ont permis d'identifier deux mécanismes de réorganisation pour les structures aux grandes échelles : un changement de signe de la vitesse transverse entre les crayons ou du tourbillon dans un sous-canal. Il est apparu qu'il semblait pertinent d'adopter l'hypothèse de Taylor pour considérer que les grandes structures 3D évoluaient comme un écoulement 2D transporté. Un gros volet de la thèse a concerné la mise en œuvre d'un code basé sur une méthode statistique pour un champ 2D dans le but de déterminer les états thermodynamiquement stables dans des géométries avec obstacles. Des similarités ont été obtenues entre les structures en REP et les états stables en 2D. Des simulations 2D ont permis d'identifier deux bifurcations possibles pour l'écoulement, qui présentent un parallèle avec les mécanismes de réorganisations 3D, et permettent ainsi de poser les bases d'une explication physique du phénomène / The analysis of fuel rod bundle flows constitute a key element of pressurized-water reactors safety studies. Indeed, an insufficient flow thermal mixing can lead to a boiling crisis, which is nefarious for the reactor safety. Numerous studies have shown the existence of reorganisation phenomena in the flow large-scale structures. This thesis work aims at improving our understanding of these phenomena, with the long-term goal of developing small-scales models suited for this type of flow. A bibliographic study has brought to light the challenges faced by simulations attempting to capture these phenomena, as well as various questions regarding their physical meaning. 3D simulations have been performed in order to study this flow ; they allowed to identify two reorganisation mechanisms for the large-scale structures consisting in a sign change for either a transverse velocity in rod-to-rod gaps or for a subchannel vortex. It appeared relevant to adopt a Taylor hypothesis in order to consider the evolution of large-scale 3D structures as transported-2D. A statistical method has then been applied to the 2D field in order to determine its thermodynamically-stable states in geometries with obstacles using the resolution of an optimization problem with a numerical calculation tool. Interesting similarities have been obtained between the PWR coherent structures and the stable states in a simplified 2D geometry. Further, 2D numerical simulations allowed to identify two different possible flow bifurcations. A parallel is drawn between these bifurcations and the two reorganizations observed in 3D simulations, laying the foundations for a physical explanation of this phenomenon

Coil supports are integral load-bearing components employed in generators andmotors. They serve the purpose of preventing excessive deformation and maintaininga stable position of the coils responsible for generating power and magnetic fieldswhen rotating. However, a problem with these coil supports is that they block theairflow aimed to cool the coils. Thus, this master thesis aimed to conduct a topologyoptimization to develop a cooling-air permeable coil support and select a suitablematerial. The new design was required to withstand 30,000 operational cycles andan overspeed test running at 120% speed without plastic deformation or failure. The material selection process was initiated and based on mechanical and physicalproperties requirements. One of these was that the material should be non-magnetic.Utilizing Ansys Granta EduPack, two materials were suggested, the reference materialcurrently used for the coil support, and a titanium alloy, Ti-6Al-4V. The subsequentstep was to create a CAD model of the original design based on technical drawingsprovided by ABB. With the generated design, finite element analysis (FEA) simulationand the topology optimization could be performed. The generated topology optimizedmodel was modified and two new models were created, one with smaller central cutoutsand one with larger central cutouts and a top surface cutout. Furthermore, a thirdmodel was created based on the fundamentals of fluid mechanics, the Rounded originalmodel. Computational Fluid Dynamics (CFD) simulations of the four models wereexecuted. The findings indicate that the design with larger central cutouts exhibited the mostsubstantial increase in airflow through and in between the coil supports, achieving a122 % improvement compared to the original design. The model satisfied the fatiguerequirement and successfully passed the overspeed test. Both the current referencematerial and the Ti-6Al4V alloy are suitable to use for coil support. However, theutilization of a titanium alloy might be deemed excessive in terms of its mechanicalproperties and cost. / Spolstöd är integrerade lastbärande komponenter som används i generatorer ochmotorer. De har till syfte att förhindra extrem deformation och bibehålla positionenför spolarna som ansvarar för att generera kraft och magnetfält när de roteras. Ettproblem med spolstöden är att de blockerar luftflödet avsett att kyla spolarna. Däravär syftet och målet med detta examensarbetet att genomföra en topologioptimeringför att utveckla luftgenomsläppligt spolstöd för förbättrad kylning samt att välja ettlämpligt material. Den nya konstruktionen är tvungen att klara av 30,000 driftcykleroch ett överspänningsprov vid 120% av hastigheten utan plastisk deformation ellerbrott. Materialvalsprocessen initierades och baserades på mekaniska och fysikaliska krav.En av dessa krav var att materialet skulle vara icke-magnetiskt. Användandet avAnsys Granta EduPack resulterade i två material, referensmaterialet som användsför att producera spolstödet i nuläget och en titanlegering, Ti-6Al-4V. Därefterskapades en CAD-modell av den ursprungliga designen baserat på tekniska ritningartillhandahållna från ABB. Med den genererade modellen kunde finita elementanalys(FEA) och topologioptimeringen utföras. Detta genererade i en topologioptimeradmodel som modifierades och lade grund till två nya modeller, en modell med mindrecentrala hål och en med större centrala hål. En tredje modell skapades dessutom,baserad på grundläggande principer inom fluidmekanik. Fluidmekanik (CFD) beräkningar av de fyra modellerna utfördes och resultatenvisade på att den tolpologioptimerade modellen med stora centrala hål hade denmest betydande ökningen i luftgneomströmning genom och mellan spolstödenmed en förbättring på 122 % jämfört med den ursprungliga designen. Modellenuppfyller även kraven på utmattning och maximal statisk spänning vid rusningsprov.Både referensmaterialet och titanlegeringen var lämpad att användas som spolstöd.Däremot kan användningen av titanlegeringen anses vara överdriven med hänsyn tilldess mekaniska egenskaper och kostnad.

La protection des opérateurs et la surveillance des ambiances de travail en cas de mise en suspension d’aérosols radioactifs, dans un local ventilé d’une installation nucléaire, requièrent la connaissance de l’évolution spatio-temporelle de la concentration en particules, en tout point du local considéré. L’estimation précise de cette concentration a fait l’objet du développement de modèles spécifiques de transport et de dépôt d’aérosols dans un local ventilé, dans le cadre d’une thèse cofinancée par l’IRSN et EDF, en collaboration avec l’IMFT. Un formalisme eulérien de glissement est utilisé pour modéliser le transport des aérosols. Celui-ci est basé sur une unique équation de transport des concentrations en particules (« Diffusion-Inertia model »). L’étude spécifique du dépôt d’aérosols en parois a permis de développer un modèle de couche limite, qui consiste à déterminer précisément le flux de dépôt de particules en parois, quels que soient le régime de dépôt et l’orientation de la surface considérée. Les modèles de transport et de dépôt finalement retenus ont été implantés dans Code_Saturne, un logiciel de mécanique des fluides. La validation de ces modèles a été effectuée à partir de données de la littérature en géométries simples, puis sur la base de campagnes expérimentales de traçage dans des locaux ventilés d’environ 30 m³ et 1500 m³. / When particulate radioactive contamination is likely to become airborne in a ventilated room, assessment of aerosol concentration in every point of this room is important, in order to ensure protection of operators and supervision of workspaces. Thus, a model of aerosol transport and deposition has been developed as part of a project started with IRSN, EDF and IMFT. A simplified eulerian model, called “diffusion-inertia model” is used for particle transport. It contains a single transport equation of aerosol concentration. The specific study of deposition on walls has permitted to develop a boundary condition approach, which determines precisely the particle flux towards the wall in the boundary layer, for any deposition regime and surface orientation.The final transport and deposition models retained have been implemented in a CFD code called Code_Saturne. These models have been validated according to literature data in simple geometries and tracing experiments in ventilated rooms, which have been carried out in 30 m³ and 1500 m³ laboratory rooms.