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No description available.

Blunt-nosed sphere-cone aeroshell vehicles have played an integral part in space exploration to date and their use is set to continue into the next decade and beyond. While these vehicles have been flight proven with four decades of heritage, design uncertainties in aft body thermal protection systems in the order of 300-400% exist due to the as yet unpredictable flowfield characteristics of the near-wake region of these vehicles at hypersonic speeds. Attempts have been made to reduce this uncertainty but current technology in the field of computational fluid dynamics (CFD) still requires phenomenological models to be developed that accurately predict base heating rates. Expansion tube experimental facilities have the potential for aiding in the reduction of this design uncertainty. However, it is not known whether the X2 or X3 expansion tubes at the University of Queensland can be employed to obtain data for assisting the development of CFD modelling techniques. A survey of the current best practices in CFD modelling techniques is presented. Preliminary CFD models have been developed to resolve the macroscopic features of the wake flows around the Mars Pathfinder aeroshell geometry. A series of experiments have been performed and the duration of time average steady heating is documented. Results of experimentation indicated that the X2 impulse machine operating in expansion tube mode is capable of generating a sufficient length of steady flow for the study of near-wake phenomena. This is documented in flow conditions using CO2 to simulate Martian flight conditions. It was also demonstrated that flow speeds and model dimensions must be matched appropriately to allow for sufficient test time. A method for the sizing of experimental models is also presented for the study of heat transfer in near-wake flow fields. Example model geometries are prescribed for a variety of flow conditions for the X2 expansion tube.

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).

Mode of access: Internet via World Wide Web. Available at http://hdl.handle.net/1947/9653. / "August, 2008" "AR No. 014-237" "DSTO-TR-2159" Includes bibliographical references.

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.

No description available.