L'étirage à froid des tubes d'aluminium extrudés améliore leur fini de surface et augmente leur résistance ; cependant cela diminue leur ductilité. Pour atteindre la ductilité exigée lors des opérations subséquentes de pliage, les tubes sont traités thermiquement après l'étirage à froid. Pour résoudre un problème industriel, ce projet vise à déterminer les conditions de traitement thermique optimales (temps et température) pour obtenir des propriétés mécaniques (limite élastique, limite ultime et allongement à la rupture) exigées par la condition T832 de l’alliage 6063 spécifiée par la norme ASTM associée et éliminer les pertes dues à des ruptures lors du pliage des tubes. De plus, le projet expose l’influence de la quantité de déformation par étirage sur les propriétés après le traitement thermique. Enfin, il cherche à déterminer si le temps de montée en température du four peut contribuer au traitement thermique afin d'augmenter la productivité du procédé. / Cold drawing of extruded aluminium tubes not only improves the surface quality but also increases their strength, however ductility of the tubes decreases. To improve the ductility required for the following bending operations, tubes are heat treated after the cold drawing operation. To resolve an industrial problem, this research aims to determine the optimal heat treatment conditions for obtaining the required mechanical properties (yield strength, ultimate tensile strength and elongation to fracture) based on the ASTM 6063-T832 temper and also avoiding scraps caused by failure during the bending operation. Moreover, this research investigates the effect of the amount of prestrain imposed by cold drawing on mechanical properties after the heat treatment. Finally, it is interesting to know if the heating period inside the furnace before reaching the targeted temperature could be exploited as part of the required heat treatment to increase the productivity of the process.

Simultaneous flow of gas-liquid in pipes presents considerable challenges and difficulties due to the complexity of the two-flow mixture. Oil-gas industries need to handle highly viscous liquids, hence studying the effect of changing the fluid viscosity becomes imperative as this is typically encountered in deeper offshore exploration. This work looks at the effect of liquid viscosity on gas-liquid flows. The work was carried out using two different pipes of 67mm and 127mm internal diameter. For the experiments carried out on the 67mm diameter pipe, air and three different liquids were used with viscosities 1, 42 and 152cp. With these experiments, the effect of viscosity on the entrainment process from the Taylor bubble in a vertical tube was investigated with the Taylor bubble being held stationary in a downward liquid flow with the use of three different gas injection methods. Taylor bubble length, the gas flow rate and the liquid flow rate approaching the stationary bubble were varied. In addition, the wake length below the stationary bubble was measured at different conditions of gas and liquid superficial velocities and comparison was made with the work by previous authors. Videos were taken with high speed camera to validate the measurement taken on wake lengths. A Wire Mesh Sensor system was placed at two different positions below the air injection point on the 67mm diameter pipe of the stationary bubble facility whose data acquisition provided time and cross-sectionally resolved information about spatial distribution. This information was used to generate time averaged void fraction, bubble size distribution and contour plots of the two-phase flow structure. A Probability Density Function (PDF) of void fraction can be obtained from the former, with PDFs of the wake section of the stationary bubbles showing that the flows are in the bubbly region while the PDF for the entire slug unit assumed that for a typical twin-peaked slug flow. The interpretation of this is that holding a bubble stationary can simulate real slug flow. Results on the bubble length measurement and gas loss into a bubble wake have shown good agreement with existing work by other authors. Experiments on the 127 mm diameter pipe were carried out because most published work on gas/liquid flow were on smaller diameter pipes with air and water, yet many of the industrial applications of such flows in vertical pipes are in larger diameter pipes and with liquids which are much more viscous than water. Another important parameter considered in the study is pressure because of its effect on gas density. This part of the research goes some way to rectify this lack and presents void fraction and pressure gradient data for sulphur hexafluoride with gas densities of 28 and 45 kg/m3 and oil (viscosity 35 times water). The gas and liquid superficial velocities were varied in the ranges 0.1-3 and 0.1-1 m/s respectively. The void fraction was also measured with a Wire Mesh Sensor system. Flow patterns were identified from the signatures of the Probability Density Function of cross-sectionally averaged void fraction. These showed the single peak shapes associated with bubbly and churn flow but not the twin-peaked shape usually seen in slug flow. This confirms previous work in larger diameter pipes but with less viscous liquids. For the bubble to churn flows investigated, the pressure gradients decreased with increasing superficial gas velocity. The change in pressure ultimately affects the density of gas in the two-phase flow mixture. Though there was little effect of pressure on void fraction below certain transitional flow rates, the effect became significant beyond these values. Different statistical analysis techniques such as power spectral density, probability density function, mean, standard deviation and time series of the acquired data have been used which also show the significant effect of pressure on void fraction at high gas density which have not been measured previously.

The transport and separation of oil and water is an essential process to the oil and chemical industries. Although transporting the mixtures is often necessary due to few reasons, it is generally beneficial to separate out the phases in order to reduce installation and maintenance costs, at the same time, avoiding safety problems. Thus, separation of liquid-liquid flows is a necessary part of many industrial processes. Hence, knowledge of two-phase flow dynamics is important for the design optimisation of separators. Therefore, the aim of this research is to investigate the feasibility of a sudden pipe expansion to be used as phase separator because it compact in design and capable for converting dispersed flow to stratified flow. In the test section, spatial distribution of the liquid-liquid phases in a dynamics flow system was visualised for the first time for by means of capacitance Wire Mesh Sensor (CapWMS), providing instantaneous information about the interface shapes, waves and phase layer evolution of oil-water flow. Visual assessment and analysis of the WMS data showed three distinct layers: an oil layer at the pipe top; a water layer at the pipe bottom and a mixed layer between them. The interfaces that form between the separated phases (oil or water) and the mixed layer were classified as oil interface or water interface. Results showed interface shapes were initially concave or convex near to the inlet of the test section and became flat further downstream the expansion, especially for water interfaces. There were no waves observed for horizontal and downward pipe orientations at all flow conditions and axial position downstream of the expansion. As for the upward inclined pipe orientation, waves were found, and they formed at position close to the inlet at all input oil volume fraction except at 0.2 OVF. The amplitude of the waves was: ~ 0.29D for 0.8 OVF; ~ 0.22D for 0.6 OVF and ~ 0.26D for 0.4 OVF. The higher the input oil volume fraction, the larger the waves become. In conclusion, the WMS results demonstrated that spatial distributions are strongly dependent on the mixture velocity, input oil fraction and inclination angles for the far position. In this present work, droplets were found to be larger near the interface. Drops were large nearer to the interface at the near position (10D) for all pipe orientations and throughout the test section for horizontal flow. The drops size decreased when the distance from the interface increased for these pipe configurations. As for the furthest position from the expansion for upward and downward inclined pipe orientation, larger droplets could also be seen at distance away from the interface and vice versa. The gravity or buoyant force is one of the contributing factors to the settling of the droplets. These forces are acting simultaneously on the droplets i.e. if the buoyant force which tends to spread the droplets throughout the pipe cross-section, is not large enough to overcome the settling tendency of gravity settling of the droplets occurs. Hence, the droplets that are non-uniformly scattered within the continuous phase begin to coalesce as they flow further downstream the pipe, producing larger drops. In addition, as the distance from expansion increased, the mixed layer becomes narrow and more drops begin to coalescence to form large drop due to increased droplet-droplet collision. Owing to these factors, results indicate that the mechanisms of coalescence occurred faster at the bottom, for water droplets and at the top, for oil droplets than the other locations in a pipe cross-section. For a better separation design, the coalescence process should occur at the aforementioned (bottom for water and top for oil) locations within the expansion pipe. However, at higher mixture velocities the mixed layer would be responsible for the smaller droplet size for horizontal and both inclinations of pipe orientation. The mixed layer dominated almost entirely in the pipe cross-section.

Lorentz-forcing spanwise travelling wave actuation in the turbulent boundary layer has been studied in a water channel at various experimental conditions (St = 139.2, 186 and 232; T+ = 17, 42 and 82). At the Reynolds number of Reτ = 388, a maximum skin friction drag reduction of 30% is achieved in some cases, while up to 22.8% of viscous drag increase is also observed. The results of the turbulent boundary layer profiles show that the turbulence intensities for both the drag-reducing and the drag-increasing cases are reduced. The higher moments of turbulence statistics such as the skewness and the kurtosis increase near the wall when T+ = 42, St = 232 in the drag-reducing case. For the drag-increasing case (T+ = 17, St = 232), the skewness and the kurtosis are decreased when very close to the wall (y+ < 6), while they are increased for y+ > 6, similar to the drag-reducing case. The reduction in the turbulent intensities as well as the changes in VITA velocity profiles suggest that the drag changes are due to the modified near-wall activities by the Lorentz forcing. Flow visualisation shows that the low-speed streaks are twisted into the spanwise directions in both the drag-reducing and the drag-increasing cases. For the drag-reducing case, the low-speed streaks are clustered together to form a wide low-speed region similar to what Du et al (2002) have found. This low-speed region seems to act as the ‘storage’ of low-speed fluid to help reduce the skin friction drag. To achieve the drag reduction, the spanwise displacement of low-speed streaks must be greater than 115 wall units in the present configuration, which compares well with the average spacing of low-speed streaks in the turbulent boundary layer. When the drag increase occurs, only pseudo-local spanwise oscillation is observed without a formation of a wide low-speed region. The pseudo-local spanwise oscillation appears to produce converging and diverging motions around the forcing-activation area. The induced streamwise vorticity layers are believed to enhance the effect of the sweep motion, which results in the increasing skin-friction drag.

Improved cooking stoves can bring significant benefits to women and children in rural African situations, due to reduced fuel consumption and improved indoor air quality. This investigation focuses on the use of Computational Fluid Dynamics (CFD) and Genetic Algorithms (GAs) to optimise a stove for Eritrea. Initial work focussed on developing a model of wood combustion in a fixed bed. An experimental investigation was carried out on regular wood cribs to determine the burn rate and temperature field above a wood fire. The experimental data was used to develop a numerical model using CFD software Fluent 6.2 and user-defined functions for the fixed bed of fuel. The model assumed that pyrolysis was limited by heat transfer through the fuel, and that char combustion was limited by oxygen diffusion to the fuel surface. Simulation results yielded a mean and maximum error of 16% and 42% respectively in fuel burn rate. In the second phase of the investigation, the numerical model of wood combustion was used as part of a larger CFD model to capture the behaviour of a complete stove. The model was compared with experimental data for rocket type stoves with different geometries. The model correctly identified the trends of fuel burn rate and heat transfer in the experimental data, though agreement with experimental values was poor and the model exhibited significant errors when altering stove height and diameter. In the final phase of the investigation, the stove model was used in conjunction with a genetic algorithm to optimise the stove shape. Two methods of genetic coding were investigated. The resulting stove is expected to half fuel consumption compared to the classic mogogo stove, though this remains to be experimentally verified.

An experimental investigation has been undertaken in a wind tunnel to study the induced airflow and drag reduction capability of AC glow discharge plasma actuators. Plasma is the fourth state of matter whereby a medium, such as air, is ionized creating a system of electrons, ions and neutral particles. Surface glow discharge plasma actuators have recently become a topic for flow control due to their ability to exert a body force near the wall of an aerodynamic object which can create or alter a flow. The exact nature of this force is not well understood, although the current state of knowledge is that the phenomenon results from the presence of charged plasma particles in a highly non-uniform electric field. Such actuators are lightweight, fully electronic (needing no moving parts or complicated ducting), have high bandwidth and high energy density. The manufacture of plasma actuators is relatively cheap and they can be easily retrofitted to existing surfaces. The first part of this study aims at characterising the airflow induced by surface plasma actuators in initially static air. Ambient air temperature and velocity profiles are presented around a variety of actuators in order to understand the nature of the induced flow for various parameters such as applied voltage, frequency, actuator geometry and material. It is found that the plasma actuator creates a laminar wall jet along the surface of the material on which it is placed. The second part of the study aims at using plasma actuators to reduce skin-friction drag in a fully developed turbulent boundary layer. Actuators are designed to induce spanwise forcing near the wall, oscillating in time. Thermal anemometry measurements within the boundary layer are presented. These show that the surface plasma can cause a skin-friction drag reduction of up to 45% due to the creation of streamwise vortices which interact with, and disrupt the near-wall turbulence production cycle.

Within the eld of hydraulics there is a growing trend towards the use of computer based models, which have proven to be an invaluable tool in engineering. A range of commercial packages is available which encompass different mathematical models and a variety of solution strategies. A number of problems can be identified with the software currently available, and as a result, research continues into developing better numerical techniques for computational hydraulics. The issues most often addressed by researchers consider the application of faster and more accurate numerical methods, many of which were originally developed for gas dynamics problems. There has been a growing trend in favour of Riemann based methods constructed within the finite volume framework. Such methods are noted for their good conservation and shock capturing capabilities. However, the computational cost of employing theses algorithms can lead to excessively long run times, particularly when higher order mathematical models are used. This often is as a result of stability constraints placed upon explicit schemes, which require the smallest possible time step permitted throughout the grid, to be applied globally. One possibility for improving this situation is to use local time stepping, whereby individual cells are advanced by their own maximum allowable time steps. To incorporate this concept into a transient model requires the development of a suitable integration strategy, to ensure that the solution remains accurate in time. Two such strategies developed for the Euler equations are considered within this thesis for application to the Saint Venant equations of open channel flow. Both techniques have been demonstrated to reduce run times and improve the quality of solutions in the regions of discontinuities. The investigation considers the the first order scheme of Roe, together with a second order extension constructed using a ux limiter approach. he eects of using an upwind based source term treatment, specifically developed for Roe's scheme, are also considered, and the source term calculations are incorporated into the LTS framework. Results are presented for a series of steady state and transient test cases, which illustrate how local time stepping can lead to reduced run times and improved solution accuracy. The results also highlight the benets of using an upwind source term treatment, particularly when variations in the channel geometry occur.

Within the bearing chamber of a gas turbine aero-engine, lubrication of the shaft and other bearings is achieved by an oil film which may become significantly disturbed by interacting with a range of chamber geometries which protrude from the chamber wall. Minimizing these disturbances and preventing possible dry areas is crucial in optimizing a bearing chambers design. In addition, multiple obstructions may be located close to one another, resulting in a more complex disturbed film profile than by individual obstacles. Prediction of the disturbance of the film is an important aspect of bearing chamber design. For analysis of the film profile over or around a local obstacle, typical bearing chamber flows can be approximated as an incompressible thin film flow down an inclined wall driven by gravity. The Reynolds number of thin film flows is often small, and for the bulk of this thesis a Stokes flow assumption is implemented. In addition, thin films are often dominated by surface tension effects, which for accurate modelling require an accurate representation of the free surface profile. Numerical techniques such as the volume of fluid method fail to track the surface profile specifically, and inaccuracies will occur in applying surface tension in this approach. A numerical scheme based on the boundary element method tracks the free surface explicitly, alleviating this potential error source and is applied throughout this thesis. The evaluation of free surface quantities, such as unit normal and curvature is achieved by using a Hermitian radial basis function interpolation. This hermite interpolation can also be used to incorporate the far field boundary conditions and to enable contact line conditions to be satisfied for cases where the obstacle penetrates the free surface. Initial results consider a film flowing over an arbitrary hemispherical obstacle, fully submerged by the fluid for a range of flow configurations. Comparison is made with previously published papers that assume the obstacle is small and / or the free surface deflection and disturbance velocity is small. Free surface profiles for thin film flows over hemispherical obstacles that approach the film surface are also produced, and the effects of near point singularities considered. All free surface profiles indicate an upstream peak, followed by a trough downstream of the obstacle with the peak decaying in a “horseshoe” shaped surface deformation. Flow profiles are governed by the plane inclination, the Bond number and the obstacle geometry; effects of these key physical parameters on flow solutions are provided. The disturbed film profiles over multiple obstacles will differ from the use of a single obstacle analysis as their proximity decreases. An understanding of the local interaction of individual obstacles is an important aspect of bearing chamber design. In this thesis the single obstacle analysis is extended to the case of flow over multiple hemispheres. For obstacles that are separated by a sufficiently large distance the flow profiles are identical to those for a single obstacle. However, for flow over multiple obstacles with small separation, variations from single obstacle solutions maybe significant. For flow over two obstacles placed in-line with the incident flow, variations with flow parameters are provided. To identify the flexibility of this approach, flows over three obstacles are modelled. The calculation of flows around obstacles provides a greater challenge. Notably, a static contact line must be included such that the angle between the free surface and the obstacle is introduced as an extra flow parameter that will depend both on the fluid and the obstacle surface characteristics. The numerical models used for flow over hemispheres can be developed to consider film flow around circular cylinders. Numerical simulations are used to investigate flow parameters and boundary conditions. Solutions are obtained where steady flow profiles can be found both over and around a cylindrical obstacle raising the awareness of possible multiple solutions. Flow around multiple obstacles is also analyzed, with profiles produced for flow around two cylinders placed in various locations relative to one another. As for flow over two hemispheres, for sufficiently large separations the flow profiles are identical to a single obstacle analysis. For flow around two obstacles spaced in the direction of the flow, effects of altering the four governing parameters; plane inclination angle, Bond number, obstacle size, and static contact angle are examined. The analysis of flow around three cylinders in two configurations is finally considered. In addition, for two obstacles spaced in-line with the incident flow, the numerical approaches for flow over and flow around are combined to predict situations where flow passes over an upstream cylinder, and then around an identical downstream cylinder. The final section of this thesis removes the basic assumption of Stokes flow, through solving the full Navier-Stokes equations at low Reynolds number and so incorporating the need to solve nonlinear equations through the solution domain. An efficient numerical algorithm for including the inertia effects is developed and compared to more conventional methods, such as the dual reciprocity method and particular integral techniques for the case of a three-dimensional lid driven cavity. This approach is extended to enable calculation of low Reynolds number film profiles for both flow over and around a cylinder. Results are compared to the analysis from previous Stokes flow solutions for modest increases in the Reynolds number.

Liquid hold-up is seen to increase as liquid viscosity and fraction of gas taken off increases suggesting corresponding increase in partial separation of phases. However, effect of liquid viscosity does not become significant until a threshold is exceeded when fraction of gas taken off equals 0.40. In all cases examined, periodicity of flow structures is observed to increase as liquid viscosity increases. Considering the results of the three investigations carried out, it can be concluded that periodicity of two-phase flow structure increases as liquid viscosity increases and transition to co-current annular flow occurs at gas superficial velocity of 21 m/s.

Air quality in urban and industrial complexes is of great importance owing to the many implications on human and environmental health. Air pollution in built-up areas is typically associated with traffic exhaust emissions. High pedestrian level concentrations are the result of a non trivial combination of pollutant sources, climate and city morphological configurations. The increase of urbanisation puts a strain on city resources, resulting in increased use of transport and a denser and more compact urban fabric. The consequence of such a change in city morphology exacerbates current human air pollution exposure. There have been several Computational Fluid Dynamics (CFD) studies on air pollution problems in urban areas, which have largely centred on employing the conventional Reynolds-Averaged Navier-Stokes (RANS) approach, and in all of these investigations, the RANS models have been reported to numerically overpredict pollutant concentration levels when compared to wind tunnel (WT) measurements. In addition, the majority of previous investigations have failed to account for the aerodynamic effects of trees, which can occupy a significant portion of typical urban street canyons. The presence of trees aggravates the pollutant concentration at pedestrian level by altering the air circulation and ventilation. Trees act as obstacles to the airflow, reducing wind velocity within street canyons and restricting air exchange with the above-roof flow. As a result fewer pollutants are dispersed out of the canyon. To address shortcomings of previous numerical investigations, the work undertaken in this project has two main objectives. The study first aims to implement Large Eddy Simulation (LES) to improve the flow and concentration predictions, and second to demonstrate the aerodynamic impacts of trees. A wall y+ approach is used to determine the computational grid configuration and corresponding RANS turbulence model. The approach is evaluated in the present numerical study and is found to be exceptionally useful in resolving flow structures near shear zones, particularly in tree-lined canyons. This allows for the appropriate mesh resolution to be selected, when taking into account a compromise between prediction accuracy and computational cost. In part one of the project, the prediction accuracy of the pollutant dispersion within tree-free urban street canyons of width to height ratios W/H = 1 and W/H=2, are examined using two steady-state RANS turbulence closure models - the standard k-ε and Reynolds Stress Model (RSM) and LES coupled with the advection-diffusion method for species transport. The numerical results, which include the statistical properties of pollutant dispersion, e.g. the mean concentration distributions, the time-evolution and three-dimensional spreads of the pollutant, are then compared to WT measurements available from the online database (CODASC, 2008) www.codasc.de. The accuracy and computational cost of both numerical approaches are compared. The time-evolution of the pollutant concentration (for LES only) and the mean values are presented. It is observed that amongst the two RANS models, RSM performs better than standard k-ε except at the centreline of the canyon walls. However, LES, although more computationally expensive, does better than RANS. A supplementary investigation is performed to illustrate that unsteady RANS (URANS) is not a suitable replacement for LES when wishing to resolve the internally induced fluctuations of flow and concentration fields. URANS fails to capture the transient mixing process. Part two of the research extends the study from the tree-free street canyons by investigating the aerodynamic influence of tree plantings. Configurations of W/H=1 with single row of trees and W/H=2 with two rows of trees are simulated. In both cases, two tree crown porosities are studied, one for a loosely (Pvol = 97.5%) and another for a densely (Pvol = 96%) packed tree crown, corresponding to pressure loss coefficients λ = 80 m-1 and λ = 200 m-1, respectively. Results of the tree-lined cases are then compared to the tree-free street canyons from the previous investigation. It is observed that the presence of trees reduces the in-canyon circulation and air exchange, thus increasing the overall concentration levels. Similar to the tree-free cases, LES performs better than RANS. In addition, it is shown that a wider street W/H = 2 with two rows of trees promotes better air ventilation and circulation with lower pollutant accumulation at pedestrian level, as opposed to a narrow street W/H = 1 with one row of trees. This is also true for tree-free cases.