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Thesis (M.S.)--West Virginia University, 2006. / Title from document title page. Document formatted into pages; contains ix, 83 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 65-67).

Thesis (M. Phil.)--University of Hong Kong, 2000. / Includes bibliographical references.

This study uses CFD methodology to simulate an advanced Diesel engine operated at higher than conventional peak cylinder pressures. The existing mathematical models for Diesel combustion, pollutant formation and wall heat transfer are improved and validated for this operating range. The fluid flow is described via the gas-phase Favre-averaged transport equations, governing the conservation of mass, chemical species, momentum and energy, based on the Eulerian continuum framework. These equations are closed by means of the k — e turbulence model. The liquid phase uses the Lagrangian approach, in which parcels, representing a class of droplets, are described by differential equations for the conservation of mass, momentum and energy. The numerical solution of the gas phase is obtained by the finite volume method applied to unstructured meshes with moving boundaries. Diesel ignition is modeled via a reduced kinetics mechanism, coupled with a characteristic timescale combustion model. Additionally, NOx and soot emissions are simulated. For the elevated cylinder temperatures and pressures, the behaviour of the thermophysical properties of the gases and liquids involved is critically examined. A near-wall treatment is applied accounting for the large gradients of thermophysical properties in the vicinity of the wall. Furthermore an alternative combined combustion and emissions modelling approach, RIF, based on the laminar flamelet concept is tested. The methodology is validated by reference to experimental data from a research engine, a constant volume pressure chamber and a high-pressure DI Diesel engine at various operating conditions. The modified near-wall treatment gives better agreement with the heat transfer measurements. The methodology predicts Diesel combustion evolution reasonably well for the elevated pressures. Best agreement was achieved using the LATCT combustion model combined with a NOx and soot model. The predictions of emissions show encouraging trends especially regarding the soot/NOx tradeoff, but require tuning of model coefficients.

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The stability of wall driven and thermally driven cavity flow is investigated for a wide range of viscous and viscoelastic fluids. The effect of inertia, elasticity, temperature gradients, viscous heating and Biot boundary conditions are of particular interest. Both destabilisation and bifurcation phenomenon are found. For Newtonian constant viscosity flow the instabilities are characterised by a critical Reynolds number which represents the ratio of inertial forces to viscous forces, and instability occurs when the inertial forces become large. For non-Newtonian viscoelastic fluids the instability is characterised by a critical Weissenberg number, which represents the ratio of elastic forces to viscous forces, and instability also occurs when elastic forces dominate the viscous forces. For thermally driven flow the instability is characterised by a critical Rayleigh number, which represents the ratio of temperature gradient to viscosity, and instability occurs when the Rayleigh number become large. In this case the instability is also characterised by both Eckert and Biot number. The work has relevance to thermal convection and mixing processes which occur in the viscous and viscoelastic fluid within the Earth's mantle. Three-dimensional steady and transient flow in a cylindrical cavity and three dimensional steady flow in a spherical cavity, are also considered for both viscous and viscoelastic fluids. Instabilities in these three-dimensional flow depend on the same parameters as the flow in square cavity.

Obtaining accurate solutions to flows that involve discontinuous features still re- mains one of the most difficult tasks in computational fluid dynamics today. Some discontinuous features, such as shear waves and material interfaces, are quite deli- cate, yet they have a profound effect on the rest of the flow field. The accuracy of the numerical scheme and the quality of the grid discretisation of the flow domain, are both critical when computing multi-dimensional discontinuous solutions. Here, the second order WAF scheme is used in conjuction with an adaptive grid algorithm, which is able to automatically modify the grid in regions of discontinuous features and solid boundaries. The grid algorithm is a combination of two successful ap- proaches, namely Chimera and Cartesian grid Adaptive Mesh Refinement (AMR). The Chimera approach is able to accurately represent non-Cartesian boundaries, whilst the AMR approach yields significant savings in memory storage and cPu time. The combined algorithm has been thoroughly validated for convection test problems in gas dynamics. The computed solutions compare well with other numerical and experimental results. These tests have also been used to assess the efficiency of the grid adaption algorithms. Finally, the approach is applied to axi-symmetric, two- dimensional, two-phase, reactive flows in the context of internal ballistics problems. Again, the computed results are compared with other numerical and experimental results.