Starting and unstarting of hypersonic air inlets

This thesis concerns a technical hurdle that must be overcome in relation to air-breathing propulsion technologies for future space access vehicles--it discusses the flow starting process in supersonic and hypersonic air-inlets. A study is conducted, with the aid of numerical simulations, based on an inviscid model of a thermally perfect gas. Effects of boundary-imposed temporal and spatial gradients on the inlet starting phenomenon are documented for the first time. It is shown that purely accelerative starting is generally not possible, for inlets of any positive contraction, unless thousands of g 's of acceleration are imposed. It is proposed that removal of frangible structures, such as fast rupturing diaphragms, be used to impose sufficiently high spatial gradients, as necessary to permit starting beyond Kantrowitz' limit. It is shown that, for a perforated diffuser, starting takes place if a sonic line, at the leading edge of a slit, occurs at an area ratio equal to, or higher than, that corresponding to Kantrowitz' limit.

Starting and unstarting of hypersonic air inlets

This thesis concerns a technical hurdle that must be overcome in relation to air-breathing propulsion technologies for future space access vehicles--it discusses the flow starting process in supersonic and hypersonic air-inlets. A study is conducted, with the aid of numerical simulations, based on an inviscid model of a thermally perfect gas. Effects of boundary-imposed temporal and spatial gradients on the inlet starting phenomenon are documented for the first time. It is shown that purely accelerative starting is generally not possible, for inlets of any positive contraction, unless thousands of g 's of acceleration are imposed. It is proposed that removal of frangible structures, such as fast rupturing diaphragms, be used to impose sufficiently high spatial gradients, as necessary to permit starting beyond Kantrowitz' limit. It is shown that, for a perforated diffuser, starting takes place if a sonic line, at the leading edge of a slit, occurs at an area ratio equal to, or higher than, that corresponding to Kantrowitz' limit.

The Sonic Surface in the Inter-Blade Channel of the Last Stage Rotor Wheel in the Steam Turbine of Large Output

The paper deals with sonic surface in a modern turbine wheel consisting of non-prismatic ultra long blades. The whole inter-blade channel is choked. Different positions and shapes of the sonic line in particular cross-sections along the span are observed. The sensitivity of sonic line formation to small changes of effective shape of the inter-blade channel in the root section and the influence of inlet angle, stagger angle and pitch/chord ratio in the tip section are discussed. The problematic of sonic line development in the case of supersonic inlet flow filed is also described. The presented work is based on results of theoretical, experimental and numerical approaches.

Understanding of flow features over a typical crew module at Mach 4

This paper presents the numerical simulations of flowfield over a typical Crew Module at Mach 4 for different angles-of-attack ranging from 0 to –25°. Detailed flow features such as contour of density gradient over the model, numerical oil flow and near wake vortex structures are captured very well in the present simulations. The location of the sonic line and its behaviour due to angles-of-attack is also captured in the simulations. TheCPdistribution on the windward and leeward side shows excellent match with the experimental results. Also, the prediction of aerodynamic coefficients shows very good agreement with the experimental results. The numerical simulation predictsCMcg,CNandCAwithin 8%, 4% and 3·5% respectively with respect to experimental values.