Les barrages sur les rivières sont des obstacles à la migration piscicole. Les passes à poissons sont des ouvrages permettant aux espèces piscicoles de migrer, autorisant le rétablissement de la continuité écologique des cours d'eau. Le but de ce travail est de mieux comprendre les phénomènes physiques présents dans les passes à poissons naturelles. Ces passes sont des canaux à forte pente, équipé de rangées de plots en quinconce. Pour valider la pertinence de l'utilisation d'un modèle numérique, l'étude s'est limitée à l'écoulement autour d'un cylindre émergent placé au centre d'un canal. Le travail est décomposé en deux parties, une expérimentale et une numérique. La partie expérimentale est conduite dans un canal transparent de 4m de long, 0,4m de large et 0,4m de hauteur. Le diamètre du cylindre est 4cm et sa hauteur 20cm (toujours émergent). Les cas étudiés sont des débits de 5, 10, 15 et 20 l/s pour une pente nulle. Les nombres de Froude sont supérieurs à 0,5 et les nombres de Reynolds, basés sur le diamètre, sont compris entre 15000 et 50000. Les écoulements ont été filmés et un algorithme de suivi de particules (PTV) a été développé. Des zones de faibles vitesses existent, même pour Fr=1, pouvant assurer des zones de refuge pour le poisson. Les forces de trainée ont été mesurées sur le plot. Les évolutions des coefficients de trainée avec le nombre de Froude et des rapports de forme de l'écoulement autour du plot ont ainsi été évaluées. La partie numérique est réalisée avec OpenFOAM pour 4 cas d'étude (Q=10 et 20 l/s, S=0 et 2%) et 2 modèles de turbulence URANS, le RNG k-epsilon et le k-omega SST. Des modélisations en 2D ont également été faites avec Telemac 2D. Les résultats obtenus ont été comparés aux résultats expérimentaux. La modélisation 2D (shallow water) est exploitable seulement pour des nombres de Froude faibles, d'où la nécessité des modélisations en 3D. Le modèle komega SST semble le mieux adapté pour reproduire les écoulements étudiés. Les vitesses locales et les structures en 3D, non quantifiables expérimentalement, ont ensuite été décrites. Les influences du fond et de la surface libre sur le sillage apparaissent clairement en provoquant des vitesses verticales et des tourbillons à grandes échelles. Enfin, une simulation en LES a été conduite. Les structures tourbillonnaires sont mieux représentées que pour les modèles URANS, mais les temps de calcul sont grands.

This work concerns the modelling of scenarios for a residential hydrogen refuelling system. Such a system is under construction within the Engineering Safe and Compact Hydrogen Energy Reserves (ESCHER) project. Non-reacting and reacting simulations are compared against experimental data before being applied to a residential garage scenario. The non-reacting simulations utilise natural ventilation, which utilises the natural buoyancy of hydrogen and vent locations to disperse flammable mixtures. This is favoured over mechanical ventilation, which could fail. The non-reacting work focuses on investigating the most suitable venting configuration for a release of hydrogen from a refuelling system located within a residential garage. Different vent configurations are examined initially before proceeding to take into account atmospheric conditions, wind, and the presence of a vehicle for the two best venting configurations. This is to determine the venting configuration that would diminish the accumulation of a flammable mixture, as well as dissipating the mixture quickest after the release has stopped. The modelling strategy utilised for this work is validated against two different sets of experimental data, prior to the investigation into residential garages. The predicted and experimental results show good agreement for the modelling procedure suggested. The reacting investigations are for both premixed and non-premixed combustion. The non-premixed combustion investigates the temperature distributions and as such the possible harm to people for such a scenario, compared against experimental data. The results show some over predictions of the temperatures. The premixed combustion investigates the potential overpressures that may occur if a homogeneous mixture was to form and ignite, within a residential garage. This work is preceded by a validation of the combustion model with the predicted results compared to data from The University of Sydney. The validation results show that the modelling strategy matches the peak overpressures accurately. The non-reacting studies show that having a lower vent opposite the release and an higher vent near the release produces the smallest flammable mixture as well as dissipating the mixture to the external surroundings quickest. The non-premixed reacting work shows good agreement with experimental results. The premixed reacting work shows that the garage would destruct with major consequences to people and surroundings. This work would be applicable to any potential usage of indoor refuelling for hydrogen vehicles, helping to determine a suitable configuration for mitigating hydrogen releases. It should be noted that all such work is geometrically dependent and as such the strategy proposed would be useful for investigating individual scenarios.

The GDI engine has a number of practical advantages over the more traditional port-fuel injection strategy, however a number of challenges remain the subject of continued research in an attempt to fully exploit the advantages of the GDI engine. These include complex in-cylinder flow fields and fuel-air mixing strategies, and significant temporal variation, both through an engine cycle and on a cycle-by-cycle basis. Despite advances in experimental techniques, the relative difficulty and cost of taking detailed measurements remains high, thus computational techniques are an integral part of research activities. The research work presented in this thesis has focused on the use of detailed 3D-CFD techniques for investigating physical phenomena of the in-cylinder flow field and fuel injection process in a single cylinder GDI engine with early injection event. A detailed validation of the numerical predictions of the in-cylinder flow field using both the RANS RNG k-ε turbulence model and the Smagorinsky LES SGS turbulence model was completed with both models showing good agreement against available experimental results. A detailed validation of the numerical predictions of the fuel injection process using a Lagrangian DDM and both RANS RNG k-ε turbulence model and Smagorinsky LES SGS turbulence model was completed with both models showing excellent agreement against experimental data. The model was then used to investigate the in-cylinder flow field and fuel injection process including research into: the three dimensional nature of the flow field; intake valve jet flapping, characterisation, causality and CCV, and whether it could account for CCV of the mixture field at spark timing; the anisotropic characteristics of the flow field using both the fluctuating velocity and turbulence intensity, including the increase in anisotropy due to the fuel injection event; the use of POD for quantitatively analysing the in-cylinder flow field; investigations into the intake valve, cylinder liner and piston crown spray plume impingement processes, including the use of a multi-component fuel surrogate and CCV of the formed liquid film; characterisation and CCV of the mixture field though the intake and compression strokes up to spark timing. Finally, the predicted turbulence characteristics were used to evaluate the resultant premixed turbulent combustion event using combustion regime diagrams.

A fully coupled system in which a vehicle s aerodynamic and handling responses can be simulated has been designed and evaluated using a severe crosswind test. Simulations of this type provide vehicle manufacturers with a useful alternative to on road tests, which are usually performed at a late stage in the development process with a proto- type vehicle. The proposed simulations could be performed much earlier and help to identify and resolve any aerodynamic sensitivities and safety concerns before significant resources are place in the design. It was shown that for the simulation of an artificial, on-track crosswind event, the use of the fully coupled system was unnecessary. A simplified, one-way coupled system, in which there is no feedback from the vehicle s dynamics to the aerodynamic simulation was sufficient in order to capture the vehicle s path deviation. The realistic properties of the vehicle and accurately calibrated driver model prevented any large attitude changes whilst immersed in the gust, from which variations to the aerodynamics could arise. It was suggested that this system may be more suited to other vehicle geometries more sensitive to yaw motions or applications where a high positional accuracy of the vehicle is required.

The latest spillway in Bergeforsen was finished in 2014. It has a 25 metres wide spillway opening capable of discharging 1500 m^3/s at full reservoir retention level. The overflow chute ends in a 35 metres wide and 100 metres long stilling basin which then converges into 25 metres wide curved tunnel leading the water flow under a railway and back into the river. During the winter, the water in the stilling basin and the tunnel freezes, creating an ice cover all the way through the channel and limiting the water passage in the tunnel. For thinner ice covers, the channel can be flushed by discharging water into the spillway, but there are concerns that a colder winter might result in a ice cover of significant thickness, not prone to cracking at water discharges. This could result in water masses flowing on top of the ice cover into an ice covered tunnel leaving it at risk of being pressurized, posing some serious safety threats to the tunnel. This report presents a full-scale 3D model of the spillway with an ice cover as well as both transient and steady-state simulation results for several discharges to examine the effect of an impenetrable ice cover in the channel. The model is verified using American Society of Mechanical Engineers policy complete with an grid convergence index study. It was found that there was no risk for pressurized flow in the tunnel. However, serious wave-run ups was observed at the tunnel entrance and in the tunnel. / <p>Slutrapporten i projektkursen F7042T (15 hp) på civilingenjörsprogrammet i Teknisk fysik och elektroteknik (INTE EXJOBB).</p>

This work presents a model of the fouling mechanism and the evaluation of compressor washing on line. The results of this research were obtained from experimental and computational models. The experimental model analyzed the localization of the particle deposition on the blade surface and the change of the surface roughness condition. The design of the test rig was based on the cascade blade arrangement and blade aerodynamics. The results of the experiment demonstrated that fouling occurred on both surfaces of the blade. This mechanism mainly affected the leading edge region of the blade. The increment of the surface roughness on this region was 1.0 μm. This result was used to create the CFD model (FLUENT). According to the results of the CFD, fouling reduced the thickness of the boundary layer region and increased the drag force of the blade. The model of fouling was created based on the experiment and CFD results and was used to calculate the engine performance in the simulation code (TURBOMATCH). The engine performance results demonstrated that in five days fouling can affect the overall efficiency by 3.5%. The evaluation of the compressor washing on line was based on the experimental tests and simulation of the engine performance. This system demonstrated that it could recover 99% of the original blade surface. In addition, this system was evaluated in a study case of a Power Plant, where it proved itself to be a techno-economic way to recover the power of the engine due to fouling. The model of the fouling mechanism presented in this work was validated by experimental tests, CFD models and information from real engines. However, for further applications of the model, it would be necessary to consider the specific conditions of fouling in each new environment.

This dissertation presents a methodology to simulate the dispersion of water droplets in the air flow typical of an Icing Tunnel. It is based on the understanding the physical parameters that influence the uniformity and the distribution of cloud of droplets in the airflow and to connect them with analytical parameters which may be used to describe the dispersion process. Specifically it investigates the main geometrical and physical parameters contributing to the droplets dispersion at different tunnel operative conditions, finding a consistent numerical approach to reproduce the local droplets dynamic, quantifying the possible limits of commercial CFD methods, pulling out the empirical parameters/constant needing to simulate properly the local conditions and validating the results with calibrated experiment. An overview of the turbulence and multiphase flow theories, considered relevant to the Icing Tunnel environment, is presented as well as basic concepts and terminology of particle dispersion. Taylor’s theory of particle dispersion has been taken as starting point to explain further historical development of discrete phase dispersion. Common methods incorporated in commercial CFD software are explained and relative shortcomings underlined. The local aerodynamic condition within tunnel, which are required to perform the calculation with the Lagrangian particle equation of motions, are generated numerically using different turbulent models and are compared to the historical K-ε model. Verification of the calculation is performed with grid independency studies. Stochastic Separated Flow methods are applied to compute the particle trajectories. The Discrete Random Walk, as described in the literature, has been used to perform particle dispersion analysis. Numerical settings in the code are related to the characteristics of the local turbulent condition such as turbulence intensity and length scales. Cont/d.

abstract: With the ever-increasing demand for high-end services, technological companies have been forced to operate on high performance servers. In addition to the customer services, the company's internal need to store and manage huge amounts of data has also increased their need to invest in High Density Data Centers. As a result, the performance to size of the data center has increased tremendously. Most of the consumed power by the servers is emitted as heat. In a High Density Data Center, the power per floor space area is higher compared to the regular data center. Hence the thermal management of this type of data center is relatively complicated. Because of the very high power emission in a smaller containment, improper maintenance can result in failure of the data center operation in a shorter period. Hence the response time of the cooler to the temperature rise of the servers is very critical. Any delay in response will constantly lead to increased temperature and hence the server's failure. In this paper, the significance of this delay time is understood by performing CFD simulation on different variants of High Density Modules using ANSYS Fluent. It was found out that the delay was becoming longer as the size of the data center increases. But the overload temperature, ie. the temperature rise beyond the set-point became lower with the increase in data center size. The results were common for both the single-row and the double-row model. The causes of the increased delay are accounted and explained in detail manner in this paper. / Dissertation/Thesis / Masters Thesis Mechanical Engineering 2015

Understanding the burning behaviour of litter fuels is essential before developing a complete understanding of wildfire spread. The challenge of predicting the fire behaviour of such fuels arises from their porous nature and from the strong coupling of the physico-chemical complexities of the fuel with the surrounding environment, which controls the burning dynamics. In this work, a method is presented to accurately understand the processes which control the burning behaviour of a wildland fuel layer using numerical simulations coupled with laboratory experiments. Simulations are undertaken with ForestFireFOAM, a modification of FireFOAM that uses a Large Eddy Simulation solver to represent porous fuel by implementing a multiphase formulation to conservation equations (mass, momentum, and energy). This approach allows the fire- induced behaviour of a porous, reactive and radiative medium to be simulated. Conservation equations are solved in an averaged control volume at a scale su cient to contain both coexisting gas and solid phases, considering strong coupling between the phases. Processes such as drying, pyrolysis, and char combustion are described through temperature-dependent interaction between the solid and gas phases. Di↵erent sub-models for heat transfer, pyrolysis, gas combustion, and smouldering have been implemented and tested to allow better representation of these combustion processes. Numerical simulations are compared with experiments undertaken in a controlled environment using the FM Global Fire Propagation Apparatus. Pine needle beds of varying densities and surface to volume ratios were subject to radiative heat fluxes and flows to interrogate the ignition and combustion behaviour. After including modified descriptions of the heat transfer, degradation, and combustion models, it is shown that key flammability parameters of mass loss rates, heat release rates, gas emissions and temperature fields agree well with experimental observations. Using this approach, we are able to provide the appropriate modifications to represent the burning behaviour of complex wildland fuels in a range of conditions representative of real fires. It is anticipated that this framework will support larger-scale model development and optimisation of fire simulations of wildland fuels.

abstract: For CFD validation, hypersonic flow fields are simulated and compared with experimental data specifically designed to recreate conditions found by hypersonic vehicles. Simulated flow fields on a cone-ogive with flare at Mach 7.2 are compared with experimental data from NASA Ames Research Center 3.5" hypersonic wind tunnel. A parametric study of turbulence models is presented and concludes that the k-kl-omega transition and SST transition turbulence model have the best correlation. Downstream of the flare's shockwave, good correlation is found for all boundary layer profiles, with some slight discrepancies of the static temperature near the surface. Simulated flow fields on a blunt cone with flare above Mach 10 are compared with experimental data from CUBRC LENS hypervelocity shock tunnel. Lack of vibrational non-equilibrium calculations causes discrepancies in heat flux near the leading edge. Temperature profiles, where non-equilibrium effects are dominant, are compared with the dissociation of molecules to show the effects of dissociation on static temperature. Following the validation studies is a parametric analysis of a hypersonic inlet from Mach 6 to 20. Compressor performance is investigated for numerous cowl leading edge locations up to speeds of Mach 10. The variable cowl study showed positive trends in compressor performance parameters for a range of Mach numbers that arise from maximizing the intake of compressed flow. An interesting phenomenon due to the change in shock wave formation for different Mach numbers developed inside the cowl that had a negative influence on the total pressure recovery. Investigation of the hypersonic inlet at different altitudes is performed to study the effects of Reynolds number, and consequently, turbulent viscous effects on compressor performance. Turbulent boundary layer separation was noted as the cause for a change in compressor performance parameters due to a change in Reynolds number. This effect would not be noticeable if laminar flow was assumed. Mach numbers up to 20 are investigated to study the effects of vibrational and chemical non-equilibrium on compressor performance. A direct impact on the trends on the kinetic energy efficiency and compressor efficiency was found due to dissociation. / Dissertation/Thesis / M.S. Aerospace Engineering 2013