No description available.

No description available.

Tidal stream energy presents challenges that will require the development of new engineering tools if designs are to harness this energy source effectively. At first glance one might imagine that tidal stream energy can be treated as wind with appropriate adjustment for fluid properties of water over air, and account taken of the harsher offshore environment; both waves and turbulence. However, it is now well accepted that the flow past turbines that are constrained by the local sea bed, sea surface, and possibly also neighbouring turbines and channel sides, will differ markedly from that of an ostensibly unblocked wind turbine. Garrett & Cummins (2007) were the first to demonstrate that operating a turbine in a non- negligibly blocked flow passage presents a different flow solution and importantly a significant opportunity to enhance the power that can be delivered by blocked turbines with the limit of power extraction exceeding the Lanchester-Betz limit for operation of unblocked wind turbines. Although it is impractical to array real turbines across the entire width of a channel it has been proposed to use short arrays of turbines making use of local constructive interference (blockage) effects; Nishino & Willden (2012) showed that although the phenomenal power limits of Garrett & Cummins are unobtainable in a real flow, a significant uplift in the limit of power extraction can be achieved for short fences of turbines arrayed normally to the flow in wide cross-section channels. However, it does not follow that rotors designed using unblocked wind turbine tools are capable of extracting any more power than they are designed for and hence the power uplift made available through blockage effects may be squandered. This thesis sets out to develop design tools to assist in the design of rotors in blocked environments that are designed to make use of the flow confinement effects and yield rotors capable of extracting some of the additional power on offer in blocked flow conditions. It is the pressure recovery condition used in wind turbine design that requires relaxation in blocked flow conditions and hence it is necessary to resort to a computational framework in which the free stream pressure drop can be properly accounted for. The tool of choice is a computational fluid dynamics embedded blade element method. As with all models with semi-empirical content it is necessary to select and test correction models that account for various simplifications inherent to the use of the blade element method over a fully blade resolved simulation. The thesis presents a rigorous comparison of the computational model with experimental data with the various correction methods employed. The tool is then used to design rotors, first for unblocked operation, with favourable comparison drawn to lifting line derived optimal Betz rotor solutions. The final objective of the study is to design rotors for operation in short fence configurations of four turbines arrayed normally to the flow. This is accomplished and it is shown that by using bespoke in situ rotor design it is possible to extract more power than possible with non-blockage designs. For the defined array layout and operating conditions, the bespoke rotor array design yields a power coefficient 26% greater than the implied Betz limit for an unblocked rotor and 4% greater than operating a rotor designed in isolation in the same array.

Worker exposure to coal dust in underground mines remains a major health hazard. This research has: 1) Analyzed the wetting characteristics of less than 10 micron dust particles using a novel micro-emulsion technology (MET) at bench scale and prototype scale with emphasis on agglomeration of dust particles, and 2) Simulate airflow and dust dispersion patterns on a longwall mining face using CFD modeling techniques to compare the current and proposed spatial distributions of water sprays around a longwall shearer. With the “Final Dust Rule” adopted by MSHA in 2014 and slated to go into full effect August 16, 2016, this research is a significant contribution to the coal industry. A suitable micro-emulsion containing 0.2% oil and 0.0125% didodecyl-dimethyl-ammonium bromide (DDAB) was identified. For assessing the wettability of coal dusts, a slightly modified version of “Fixed Time Wettability” or FTW (Chugh et al., 2004) was employed. These wettability tests however, did not yeild true wettability using the MET. An analysis for both unwetted and wetted portions of coal dust using particle size distribution curves (PSD) confirmed agglomeration when treated with the emulsion. For the unwetted portion, 96.6% of the particles had sizes greater than 25 μm after treatment with MET. Similar data for wetted dust was 100%. Experiemental studies in a 4 ft x 4ft x 10 ft chamber showed 12-15% improvement in respirable dust when using MET as compared to water alone.. Validated computational fluid dynamics (CFD) models were used to study airflow patterns and the interaction between sprays and airflow for designing both engineering and administrative controls around a longwall face. Two important zones – low air velocity (LAV) and recirculation (RC) – were identified around the model of a longwall face. These zones were located: 1) Behind the headgate drum and 2) Above the shearer chassis. Analysis of a modified geometric configuration of sprays on the shearer chassis showed improved coverage for wetting the dust on the longwall face. Numerical modeling comparisons were made between current spray systems and spray systems proposed by Dr. Y. P. Chugh using the concepts of “Continuous and Discrete Phase Modeling”. Analyses included changes in airflow patterns caused by spray systems and dust dispersion tracks generated from the cutting face. Chugh’s spray system was able to effectively eliminate RC zones existing above the shearer body, thereby minimizing the extent to which coal dust enters the walkway of the longwall face where workers are located. The proposed spray system used concepts of multiple wetting points for dust, air-locks, and venturi to wet the dust and direct the dust-laden air from mine workers. These improvements can be used in longwall mines as engineering controls for meeting new dust control standards.

Dans un contexte international de transition énergétique, l’amélioration des systèmes de production d’électricité est un élément clé. Ainsi, l’optimisation de ces systèmes, ou des composants les constituant, vise à maximiser leur efficacité, afin de convertir au mieux une source d’énergie en électricité. C’est notamment le cas des cycles de Rankine, qui font l’objet de nombreuses études pour en améliorer le rendement. La présente étude se focalise sur un composant de ce cycle vapeur : le condenseur, chargé de condenser la vapeur en sortie de turbine. Un modèle numérique est développé afin de caractériser les performances thermiques et hydrauliques de cet échangeur de chaleur. Il fait appel à une technique d’homogénéisation locale, l’approche par milieux équivalents, pour estimer les transferts thermiques, dans le cas d’un échangeur de type tubes-calandre. Pour ce faire, chacun des éléments constitutifs de ce modèle est présenté en détails, puis validé. Les principales innovations de ce modèle sont sa précision accrue, car il est capable de renseigner les performances de chaque tube, et la combinaison de corrélations utilisées, dont le choix est appuyé par une étude bibliographique. Avec le niveau de précision proposé, le modèle permet finalement d’améliorer les performances locales de l’échangeur. / Within a worldwide energy transition, the enhancement of electricity production systems plays a keyrole. Thus, the optimisation of these systems, or their constitutive components, aims at improving their efficiency, in order to better convert a energy source into electricity. In particular, it covers Rankine cycles, that numerous studies deal with, focusing on improving their performance rating. The current study is only about a single component of this steam cycle : the condenser, which is charged of condensing steam at the ouput of the turbine. A numerical modelling of the condenser has been carried out, in order to characterize its thermal and hydraulic performances. It involves an homogenization method, the porous media approach, to asses the thermal transfer, in the case of a shell-and-tube heat exchanger. To do so, each constitutive component of this model is described and validated. The main innovative aspects of this model are its increased precision, since it can give information about each tube’s performance, and the correlations’ combination, which choice is based upon a bibliographic study. With the reached precision, the model enable the user to improve the local performances of the heat exchanger.

The shape of bridge deck sections used for long-span suspension bridges has evolved through the years, from the compact box deck girders, to twin box and multi-box decks sections, which proved to have better aerodynamic behaviour, and to bring economic advantages on the construction material usage side. This thesis presents a study of a new type of multi-box bridge deck for the Megane Bridge, consisting of two side decks for traffic lanes, and two middle decks for railway traffic, connected using stabilizing beams. Aerodynamic static force coefficient measurements were performed on a section model with a scale of 1:80, for Reynolds numbers up to 5.1 × 105 under angles of attack from -10° to 10°. Also there-dimensional CFD simulations were performed by employing a Large Eddy Simulation (LES) algorithm with a standard Smagorinsky subgrid-scale model, for Re = 9.3 × 107 and angles of attack 𝛼= -4°, -2°, 0°, 2° and 4°. The experimental and numerical results were compared with respect to accuracy, sensitivity, and practical suitability. Furthermore, the aerodynamic character for each individual decks including static coefficients, wind flow pattern and pressure distribution were studied through CFD simulation. ILS (Iterative Least Squares) method was applied to extract the flutter derivatives of Megane section model based on the results obtained from free vibration tests for evaluating the flutter stability. A comparison of the flutter derivatives was carried out between bridges with different deck configurations and the results are included in this thesis.

Biomass fuel is considered a promising substitute for traditional fossil fuels. Amid a great variety of methods for converting the energy in biomass fuel into usable energy, direct combustion is still the dominant technology employed by industry. Because biomass fuel possess a much wider range of physical and chemical properties than fossil fuel, its combustion behavior is similarly diverse (and typically differs from fossil fuel), with a similar range seen in emissions characteristics. To address the variability the fuel stream imposes on the system, this work endeavors to use numerical modeling to investigate biomass combustion in a stoker boiler to provide physically insightful details while requiring minimal time and effort relative to the traditional experimental approach. In the first part of this work, a comprehensive model was developed to investigate the co-firing of different kinds of biomass including oat hulls, wood chips and natural gas with coal in a stoker boiler located in the Power Plant of the University of Iowa. Later, this model is employed in the optimization of the air supply system and plans for efficiently injecting light weight biomass, such as oat hulls, into the stoker boiler. The other key problem is in NOx prediction and reduction for the stoker boiler. This was by combining a standard CFD model describing the turbulent dynamics and combustion with several sub-models specifically developed for this study to model the fuel bed, fuel particle movement, and fuel gasification. To verify and baseline these sub-models, a series of experiments are performed, including a temperature measurement campaign for coal combustion in the boiler, a chemical lab analysis of oat hull chemical characteristics, an experiment measuring oat hull particles' physical properties, and a high-heating-rate gasification test of oat hulls. In particular, the stoker boiler temperature measurements are unique in the number of points measured and the range of firing conditions. The simulation showed that for the co-firing of oat hulls with coal, the flame temperature decreased with increasing oat hull fraction. The oat hull particles follow the flow and burn in suspension due to their light weight. The simulation showed that increasing injection velocity could slightly reduce the peak temperature and thereby reduce NOx levels. It was also observed that there is a critical velocity above which the trend of decreasing CO2 is reversed. The co-firing of other types of biomass such as wood chips and natural gas in the stoker boiler were also studied. The result of co-firing wood chips shows that adding wood chips decreases the flame. The flame zone is also shortened when compared to pure coal, primarily resulting from a higher oxygen environment above the coal bed due to the high oxygen content of the wood chips. Co-firing natural gas with coal resulted in the high temperature zone shifting from the back wall closer to the front wall, significantly reducing the overall flame length. The level of predicted NOx agreed very well with the experimental data. The simulations showed that injecting Urea with the secondary air system on the front wall can greatly reduce the NOx level inside the boiler for minimal cost and effort.

This thesis focuses on CFD analysis of the Aircar 5.0 flying car prototype. The theoretical part covers basic information about the connection between the aerodynamics of airplanes and cars as well as cars themselves. The computational part begins with the calibration of the mathematical model, continues with the CFD simulations, which have the role to determine basic aerodynamic characteristics of the Aircar in vehicle mode. There are several configurations tested to find out their influence on aerodynamic stability and their advantages and disadvantages are summed up in the conclusion chapter.

This thesis is about problematics of creating Computational Fluid Dynamics (CFD) model suited for analysis of airflow around sitting passive person. Thesis includes analysis of velocity field distribution, thermal distribution and thermal losses in the surroundings of sitting thermal dummy (computational model) and comparison of these values with experimental measurements. Thesis is a part of large experimental research (this research is not included here) focused on creating of functional method used for person-surrounding airflow analysis in future commercial use.

he primary objective of this study is to validate and/or identify issues for available numerical methods and turbulence models in OpenFOAM 2.0.0. Such a study will provide a guideline for users, will aid acceptance of OpenFOAM as one of the research solvers at institutions and also guide future multidisciplinary research using OpenFOAM. In addition, a problem of aerospace interest such as the flow features and vortex breakdown around a VFE-II model is obtained for SA, SST RANS and SA-DDES models and compared with DLR experiment. The available numerical methods such as time schemes, convection schemes, P-V couplings and turbulence models are tested as available for a fundamental case of a backward facing step for RANS and Hybrid RANSLES prediction of fully turbulent flow at a Reynolds number of 32000 and the OpenFOAM predictions are validated against experimental data by Driver et.al and compared with Fluent predictions.