The thesis describes an investigation into the turbulent flow existing in the two limiting designs of spark ignition engine combustion chamber, i.e. 'squish' and cylindrical disc designs. The analysis is concentrated on the compression stroke and the early part of the expansion stroke. The application of hot-wire anemometry to such work is described especially with regard to anemometer adjustment for optimum frequency response and hot wire probe calibration. The latter was achieved by utilizing an analytical procedure in which a heat balance of the wire was generated. The varying effects of temperature, pressure and flow velocity on the wire's convective heat loss characteristics were catered for by the Nusselt Number-Reynolds Number relationship of Collis and Williams. Excellent calibrations were achieved.

Annular vaneless diffusers have been studied both experimentally and theoretically to investigate their flow behaviour and performance. The experimental work was carried out on large models of a conical diffuser and a curved diffuser with initial contraction. Besides steady inlet conditions a simulated impeller discharge flow with a jet-wake pattern was investigated. For both conditions of steady and unsteady flow the curved diffuser gave better performance and improved stability. The jet-wake flow proved to have no significant effect upon the performance of either diffuser. The conical diffuser exhibited reversed flow on the hub which increased with mass flow reduction, and when the mass flow was low separation extended from outlet to inlet and strong low frequency pulsations of the flow were initiated. This pulsating flow phenomenon was explained as a rotating stall. Large areas of reversed flow or any flow pulsations were not detected in case of the curved diffuser. An analytical direct solution of the inviscid flow through annular vaneless diffusers of any geometry was developed on the basis of the streamline curvature approach. The solution was obtained under the assumption of a linear distribution of flow parameters. The direct solution agreed quite well with known numerical methods and with experimental results up to separation. While separation itself was well predicted, the solution failed to predict any decrease in flow distortion which was observed experimentally; this was due to the nature of the assumptions within the inviscid analysis. The direct inviscid solution was combined with a boundary layer calculation method from the literature to provide a simultaneous solution of the inviscid core and boundary layer interaction. The calculation method gave good results in the case of non-separated flows. It is felt that this calculation method could be further improved by the inclusion of separation and curvature effects in the boundary layer equations.

Three types of annular diffusers associated with radial and mixed flow turbocharger compressors have been studied both experimentally and theorticaly. The investigations have been carried out on model diffusers six times larger than the normal turbocharger in order to enable detailed flow traverse measurements to be carried out. These measurements have been obtained using both a five hole yaw probe and a hot wire anemometer in order to observe the development of the flow profiles throughout the diffuser with particular reference to flow stability. To measure the onset and development of unstable flow flush mounted wall pressure transducers were employed. Radial, curved annuler and straight annuler diffusers have been tested in order to study their relative merits. Two curved diffusers, which are used with mixed flow compressor impellers, have been studied. It has generally been observed that the straight annular diffuser was the least stable, with the radial diffuser having the best stability characteristics. For mixed flow compressor designs, therefore, the curved annular diffuser, which turns the flow from the conical to radial direction, is to be prefered. The theoretical analysis employed the finite element method to solve the basic Navier-Stokes equations using a stream function-vorticity formulation, with the common two equation, k-€ turbulence model. In order to obtain solutions at high Reynolds numbers a dynamic mesh system was used which solved for the required properties at the centre node only using the variational method. The mesh was then regenerated so that each non-boundary node become a centre node in turn. The theoretical analysis has been used to study the effect of inlet velocity profiles upon the stability of the diffuser. The analysis indicated the type of velocity profiles which should be avoided if possible.

The main objective of the research was to develop a means of numerically predicting the turbulent flow field in a baffled agitated vessel. This has been achieved by way of the 'k-e' model of turbulence. An extensive review of the literature on turbulence modelling is given to support that choice. A range of experimental studies concerning the flow in an agitated vessel, which is driven by a turbine having flat vertical blades, is reviewed for the purposes of validating predictions, and setting boundary conditions. Qualitative agreement only is found between the predictions and experimental data for the three mean velocity components at places where such data is available. The vertical plane flow pattern is in qualitative agreement with observations. This will remain the case until more detailed experimental measurements are made. Swirl velocity predictions are much less certain than the vertical plane components, however. This is attributed to the assumption that gradients in the circumferential direction can be neglected. To account directly for swirl reducing baffles, it is shown that a specially constructed source term in the swirl momentum equation, may lead to a realistic simulation of their effect. Comparisons of turbulence predictions are difficult to make in view of a general lack of reliable data. The results of this work are encouraging however, in that impeller stream turbulence is shown to be highly non-homogeneous, while turbulence in the recirculation zones is homogeneous by comparison, except near walls. Furthermore, turbulence variable distributions seem to be qualitatively correct though magnitudes are much less certain. The integrated rate at which turbulence kinetic energy is dissipated into heat, is predicted to be equally divided between the impeller stream and recirculation zones. Finally, it is shown that there is much scope for improving the model through a closer examination of impeller boundary conditions, by adapting more appropriate models to simulate baffle effects, and from wider comparison with experimental data by varying the system geometry.

Considering the gap in available information and the need of the industries such as oil and gas production, energy, and food processing, this study focuses on the two phase flows around bends in process pipe lines. The aim of this study is to investigate the influence of 90° bends on the gas-liquid two phase flow behaviour in vertical and horizontal orientations using advanced two-phase flow measuring techniques. An experimental study has been conducted using silicone oil with a viscosity of 5 mPa.s and air to examine the transitional flows around 90° bends of 68 mm internal diameter (ID) with different configurations. Experiments were conducted at ambient conditions in an open system which consists of a 68 mm ID riser of 4.5 m long, vertical upward 90° bend and two horizontal sections of a 9.2m and 5.5m long in series with a horizontal 90° bend in between. The experimental matrix comprises 60 combinations of gas and liquid superficial velocities, ranging from 0.045 m.s-1 to 3.21 m.s-1 and 0.15 m.s-1 to 0.53 m.s-1 respectively. The phase distributions within the pipes were measured using Electrical Capacitance Tomography (ECT) and Wire Mesh Sensors (WMS). The behaviour of the flow was examined qualitatively using high speed imaging. To study the flow development in the riser, both ECT and WMS were placed in series and moved along three axial locations downstream of the mixing section. During the experiments at the bends, the ECT was kept immediately upstream while the WMS was moved to different positions downstream of the bend. The cross-sectional void fraction time series from the ECT and the WMS were used to quantify the main hydrodynamic parameters of the flow including cross-sectional averaged void fraction, bubble size distribution, radial void fraction profiles, slug length, slug frequency, void fraction in liquid slugs, and the slug bubble velocity. Results were compared against the available slug flow correlations. The results show that the phases separate shortly after the vertical to horizontal bend leading to stratified or wavy stratified flow. Beyond a certain threshold of the gas flow rate and liquid level, onset of slugs can be observed at a certain distance downstream of the vertical upward bend. This work suggests that the formation of hydrodynamic slugs downstream of the vertical upward bend is independent of the inlet conditions upstream. The horizontal bend, unlike the vertical upward bend, has a minor influence on the flow evolution, particularly slug flow. This is due to the influence of gravitational force on phase separation and its subsequent effect on the change of momentum in the vertical bend. The flow structures, mainly slugs and disturbance waves, are slightly accelerated as they pass through the horizontal bend with minimum change to the structure frequency and gas holdup within liquid slugs. Most of the existing correlations do not predict the measured void fractions in this work as those correlations were essentially limited to the conditions they were developed for as the basis of them lies in the curve fitting. In this work, the higher viscosity and lower surface tension led to higher gas holdup in liquid slugs causing the discrepancy.

This thesis is concerned with the study of two independent problems. Chapter 2 is devoted to the development of a new representation for the dynamic Green's tensor for a layered medium. No completely closed solution is possible and the objective here is to develop a representation that is more amenable to computation than the existing representations (Cagniard (39), Willis (73)). The representation derives from a reduction of the integrals required for the inversion of the terms in a "generalized ray" series. For the three-dimensional (point source) problem the final solution requires either a single integration (isotropic layers) or two integrations (anisotropic layers) over contours that are independent of time t and position x. The integrand is a simple explicit function, much of which is independent of x and t and may be tabulated when the solution is required for a range of values of x and t. The remainder of this thesis examines the time-harmonic response of thin, elastic, fluid-loaded plates stiffened by attached parallel beams. The sound radiated by such structures has been studied by many authors but few have been concerned with the motion of the plate. Chapters 3, 4 and 5 of this thesis examine plates stiffened, respectively, by finite, infinite, and semi-infinite arrays of beams. In chapter 3, Fourier transforms are used to obtain a set of simultaneous equations for the transformed displacements and rotations at the beams. The inverse transform of the solution to this set of equations is evaluated asymptotically. In chapters 4 and 5 the stiffening beams are equally spaced. The equations are formulated in terms of discrete convolutions and a transform, related to the modified Z-transform, is used (together with the Wiener-Hopf technique in chapter 5) to obtain the solution. Asymptotically, the motion of the stiffened regions of the plate has the form of a Floquet wave.

This study is concerned with a variable geometry inward flow radial turbine for turbocharging Diesel engines. A detailed theoretical and experimental investigation in both the stator and rotor is presented. The finite element method being applied for the flow analysis. The finite element procedure was initially developed by applying it to an isolated aerofoil prior to the further application to cover a circular cascade of blades as encountered in the volute-nozzle assembly. In the rotor, only the hub-shroud analysis was carried out and the results compared with an existing streamline curvature technique. It was shown that the finite element method required less computaional time and was more generally applicable to complex geometric configurations than the streamline curvature technique. Experimentally, the turbine performance was evaluated with and without exhaust diffusers and with a number of nozzle rings with different restrictions. It was shown that the maximum restriction resulted in high losses due to the flow mismatching at nozzle inlet because of the sudden area change, and relatively low efficiencies resulted. The effect of swirl, resulting from off-design operation, on the diffusers was analysed with three conical diffusers. The results show that low swirls of the order of 10%, has a beneficial effect on the pressure recovery coefficient for wide angle diffuser.

This work contained in this thesis is the result of an industrial and academic collaboration, designed to investigate and further the present knowledge of dense turbulent dispersions. Experiments were conducted to provide support and experimental validation to a CFD code being simultaneously developed, which was able to give insight into these types of flows. Additional to this support, the aim of this thesis was to also further knowledge of key topics in this field. The experimental methodology chosen was to use a mixture of Particle Image Velocimetry and Particle Tracking Velocimetry. To discriminate between particle and liquid phases, two approaches were adopted, depending upon the experiment. In one approach, fluorescent dyes were used to tag one phase, whilst optical filters were applied to the camera lenses. In the second approach, a size-based binary mask was applied to a single image, in order to remove phase information and produce two sets of images. A number of different analysis techniques were researched and developed as part of this thesis. The performance of particle tracking algorithms was assessed to ascertain their most suitable usage. A number of different algorithms, designed to characterise particle positions, were validated against known test cases. These included the Box Counting Method, a Voronoi analysis, and Radial Distribution Functions. A further technique, known as the Particle Potential method, was also developed to characterise local clustering. Two experiments were undertaken throughout this project, both of which were developed from scratch so that full control was assured over all experimental parameters. A vertical channel experiment was designed to assess the injections of particles into a rectangular channel. These experiments allowed for an ideal test case of highly concentrated particles, without the need to achieve optical visibility through a dense solution. The experiments also provided an early test of a Refractive Index Matching candidate pair; hydrogel particles and water. The second experiment was known as the Circulating Dispersion Rig, which was designed to pump a slurry in a continuous loop in a cylindrical pipe. These experiments, due to the geometry used and dense nature of the slurry, were reliant upon trying to achieve optimum optical visibility, and so hydrogel/water mixtures were tested in advance against other, more well-utilised pairings. The experiments conducted have provided some insight into the nature of particles in turbulent flows, in particular their clustering properties. Clustering was assessed under various concentrations. Key results included analysis of these clusters using a Voronoi diagram technique, which identified four key types of cluster structure, and the parameters under which these form. Collision probabilities of particle pairs were also assessed, using Particle Tracking data and computation of relative velocities. Such information is of importance for experimental validation of CFD codes relating to dispersed two-phase flows, where particle-particle coupling must be assessed in order to provide accurate solutions. The key drive towards the future, should further experiments be desirable, would be to investigate the improvement of optically matching liquids and solids, which was felt to be the limiting factor towards achieving measurements at even higher concentrations. However, these experiments show some progress can be made in making measurements of four-way coupled turbulent flows.

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Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2006. / Includes bibliographical references (leaves 133-141). Also available in electronic version.