The short range dispersion in the atmosphere of buoyant gases, such as hot air or natural gas, may be hazardous and dangerous. The available methods for studying this problem were reviewed. Wind tunnel studies were considered to be the most suitable method for studying near-field dispersion, and methods for accurately modelling the nearfield behaviour of a buoyant plume of gas were examined. The experiments were performed in the Oxford University 4m x 2m low speed wind tunnel at a model scale of 1:200. The mean trajectory and rate of spread of a buoyant plume from a 60 m high (full-scale) stack were measured in the presence of a simulated natural wind. The exact similarity requirements were derived from dimensional analysis and from the equations of motion. In practice, it is not possible to match all the necessary dimensionless groups and exact scaling of the exit gas density ratio and the exit Reynolds number is often relaxed. A series of experiments was performed to examine the effect of these two groups on mean plume behaviour, with the intention of providing guidance for correct simulation of plume dispersion at reduced-scale. The exit density ratio was found to have little effect on the near-field plume behaviour, provided all the other dimensionless groups were matched. Plumes with low Reynolds number were found to rise significantly higher than plumes with higher 'turbulent' Reynolds numbers. This difference in trajectory could not be correlated with the plume exit momentum flux. The effect of the cross-flow on near-field dispersion was examined by performing experiments in four different simulations of the earth's atmospheric boundary-layer. The behaviour of the plume was found to be sensitive to both the velocity profile and the turbulence intensity of the cross-flow. To study dispersion in the wind tunnel, the cross-flow should be an accurate simulation of the velocity profile and turbulence intensity components of the natural wind.

A series of experiments has been conducted for comparison with the results of a computer code called CHYMES. It is intended to calculate the coarse mixing of molten metal with water by solving the equations of the Separated Flow Model. These are derived by volume averaging and the terms that relate them to the particular case of participate flow are discussed. An experimental apparatus that is compatible with CHYMES and coarse mixing has been constructed which projects a jet of ball bearings into a thin tank of water. Experiments over a wide range of conditions were conducted at room temperature. Owing to practical difficulties only one, poorly controlled experiment with hot ball bearings was performed. Under nearly all sets of conditions an arrow-shaped plume was obtained. The speed of penetration of the plume varied little with changes in experimental conditions. The width of the plume was most strongly influenced by the widths of the tank and the jet. The individual paths of some particles were followed; it appeared that their motion was mostly dependent on their position in the plume. A model of the plume is proposed, based upon its front being impermeable to water in the vertical direction. Much of the detail of the experimental plumes was not present in the computational results and they responded differently to changes in conditions. It is proposed that this is a result of the different forms of the two sets of plumes. To rectify this an experimental plume was volume averaged. A method to determine a suitable averaging volume size is described. The process results in a plume similar to the computational ones. The length scales required for volume averaging to be successful are discussed and the possibility that this method is inappropriate for describing coarse mixing is admitted.

The subject of the thesis is concerned with the study of the turbulent spreading and the gravity spreading processes in surface jets and surface plumes influenced by the cross-flow. A total of five different discharge and cross-flow configurations were under investigation. They are, namely, (i) submerged jets in unconfined cross-flow, (ii) surface jets in deep and shallow cross-flows, (iii) surface plumes in deep cross-flow, (iv) full-depth jets in cross-flow and (v) full-depth plumes in cross-flow, reported in Chapters IV, V, VI, VII and VIII respectively. / The effect of the gravity stratification, the effect of the free water surface and the confined effect of the channel bottom on the spreading of the turbulent flows have been determined from control experiments. The experimental data have been correlated in a unified manner, using suitable scales and dimensionless parameters. They are also related to a general integral formulation, established for this type of problems. / The results of an extensive series of previous experimental investigations, of related problems of jets and plumes in cross-flow have been reanalysed and they are integrated into the various parts of the thesis to complement and confirm the present investigation. / On the whole, the thesis has succeeded in providing a general description of the turbulent spreading and the gravity spreading processes in flows of different discharge and cross-flow configurations.

The generation and evolution of internal solitary waves by intrusive gravity currents and river plumes are examined in an axisymmetric geometry by way of theory, experiments and numerical simulations. Full depth lock-release experiments and simulations demonstrate that vertically symmetric intrusions propagating into a two-layer fluid with an interface of finite thickness can launch a mode-2 double humped solitary wave. The wave then surrounds the intrusion head and carries it outwards at a constant speed. The properties of the wave's speed and shape are shown to agree well with a Korteweg-de Vries theory that is derived heuristically on the basis of energy conservation. The numerical code is also adapted to oceanographic scales in an attempt to simulate the interaction between the ocean and a river plume emanating from the mouth of the Columbia River. Despite several approximations, the fundamental dynamics of the wave generation process are captured by the model.

Thesis (Ph.D.)--University of Wollongong, 2005. / Typescript. Includes bibliographical references: leaf 232-245.

Thesis (Ph. D.)--University of Washington, 1994. / Vita. Includes bibliographical references (leaves [187]-199).

Thesis (M.App.Sc.) - Carleton University, 2006. / Includes bibliographical references (p. 144-146). Also available in electronic format on the Internet.

Thesis (M.S.)--Michigan State University. Dept. of Geography, 2008. / Title from PDF t.p. (viewed on Aug. 11, 2009) Includes bibliographical references (p. 108-112). Also issued in print.

Thesis (Ph.D.)--University of Delaware, 2009. / Principal faculty advisor: A.D. Kirwan, College of Earth, Ocean, & Environment. Includes bibliographical references.

Thesis (M. S.)--Chemistry and Biochemistry, Georgia Institute of Technology, 2009. / Committee Chair: Janata, Jiri; Committee Member: Lyon, Andrew; Committee Member: Weissburg, Marc.