Mach 4 and Mach 8 axisymmetric nozzles for a shock tunnel

The performance of two axisymmetric nozzles which were designed to produce uniform, parallel flow with nominal Mach numbers of 4 and 8 is examined. A free-piston-driven shock tube was used to supply the nozzle with high-temperature, high-pressure test gas. The inviscid design procedure treated the nozzle expansion in two stages. Close to the nozzle throat, the nozzle wall was specified as conical and the gas flow was treated as a quasi-one-dimensional chemically-reacting flow. At the end of the conical expansion, the gas was assumed to be calorically perfect, and a contoured wall was designed (using method of characteristics) to convert the source flow into a uniform and parallel flow at the end of the nozzle. Performance was assessed by measuring Pitot pressures across the exit plane of the nozzles and, over the range of operating conditions examined, the nozzles produced satisfactory test flows. However, there were flow disturbances in the Mach 8 nozzle flow that persisted for significant times after flow initiation

Injection of clarity needed?

The legal status of children who stay in hospital for three months or longer gives rise to considerable confusion among managers in social services and social work departments. And the number of young people affected is significant. NHS statistics for the year ending 31 March 2000 suggest that in England around 2,800 children aged 0-19 on admission were discharged after spending more than two months in hospital, as were more than 500 children in Scotland. (A small number of these would have been discharged as adults.) A two-year study, commissioned by the Joseph Rowntree Foundation1 and carried out by the universities of Stirling, Durham, Newcastle and York, investigated the numbers, characteristics and circumstances of children and young people with complex needs who spend long periods in health care settings. Interviews were conducted in England and Scotland with 11 social services or health managers responsible for these children. The findings show a worrying degree of uncertainty about the position of young people who find themselves in a hospital or other health care setting for at least three months. One social services manager believed such children become looked after under the terms of the Children Act 1989. Another said children are not formally looked after but nevertheless receive the same services and safeguards as those who are. One Scottish social work manager did not know whether children going into health care settings for short-term (respite) care are looked after or not. And discussion with the research team's advisory group indicated that the confusion is not confined to our fieldwork areas

Shock Tunnel Studies of Scramjet Phenomena

Work focussed on a large number of preliminary studies of supersonic combustion in a simple combustion duct - thrust nozzle combination, investigating effects of Mach number, equivalence ratio, combustor divergence, fuel injecting angle and other parameters with an influence on the combustion process. This phase lasted for some three or four years, during which strongest emphasis was placed on responding to the request for preliminary experimental information on high enthalpy effects, to support the technology maturation activities of the NASP program. As the need for preliminary data became less urgent, it was possible to conduct more systematic studies of high enthalpy combustion phenomena, and to initiate other projects aimed at improving the facilities and instrumentation used for studying scramjet phenomena at high enthalpies. The combustion studies were particularly directed towards hypersonic combustion, and to the effects of injecting fuel along the combustion chamber wall. A substantial effort was directed towards a study of the effect of scale on the supersonic combustion process. The influence of wave phenomena (both compression waves and expansion waves) on the realization of thrust from a supersonic combustion process was also investigated. The effect of chemical kinetics was looked into, particularly as it affected the composition of the test flow provided by a ground facility. The effect of injection of the fuel through wall orifices was compared with injection from a strut spanning the stream, and the effect of heating the fuel prior to injection was investigated. Studies of fuel-air mixing by shock impingement were also done, as well as mass spectrometer surveys of a combustion wake. The use of hypersonic nozzles with an expansion tube was investigated. A new method was developed for measuring the forces acting of a model in less than one millisecond. Also included in this report are listings of published journal papers and conference presentations

Scramjet sidewall burning: Preliminary shock tunnel results

Experiments performed with a two dimensional model scramjet with particular emphasis on the effect of fuel injection from a wall are reported. Air low with a nominal Mach number of 3.5 and varied enthalpies was produced. It was found that neither hydrogen injection angle nor combustor divergence angle had any appreciable effect on thrust values while increased combustor length appeared to increase thrust levels. Specific impulse was observed to peak when hydrogen was injected at an equivalence ratio of about 2. Lowering the Mach number of the injected hydrogen at low equivalence ratios, less than 4, appeared to benefit specific impulse while hydrogen Mach number had little effect at higher equivalence ratios. When a 1:1 mixture by volume of nitrogen and oxygen is used instead of air as a test gas, it is found that hydrogen combustion is enhanced but only at high enthalpies

Further shock tunnel studies of scramjet phenomena

Scramjet phenomena were studied using the shock tunnel T3 at the Australian National University. Simple two dimensional models were used with a combination of wall and central injectors. Silane as an additive to hydrogen fuel was studied over a range of temperatures and pressures to evaluate its effect as an ignition aid. The film cooling effect of surface injected hydrogen was measured over a wide range of equivalence. Heat transfer measurements without injection were repeated to confirm previous indications of heating rates lower than simple flat plate predictions for laminar boundary layers in equilibrium flow. The previous results were reproduced and the discrepancies are discussed in terms of the model geometry and departures of the flow from equilibrium. In the thrust producing mode, attempts were made to increase specific impulse with wall injection. Some preliminary tests were also performed on shock induced ignition, to investigate the possibility in flight of injecting fuel upstream of the combustion chamber, where it could mix but not burn

Effect of Boundary Layer Thickness and Entropy Layer on Boundary Layer Combustion

This project investigates the possibilities of scramjet combustor performance enhancement by reducing the skin friction through boundary layer combustion. Experiments were conducted in the T4 Stalker tube to investigate the influence of boundary layer thickness and entropy layers on the ignition of a hydrogen air mixture near the wall of a constant area duct. The hydrogen was injected tangentially from a slot of annular cross section after an “injector” of constant area captured flow from a Mach 4 nozzle. Injectors of two different lengths and nose radii were employed to vary the thickness of the boundary layer at the injection location as well as the temperature of the gas near the walls and within the entropy layer created by the leading edge shocks of blunted leading edges. Results are presented of CFD simulations of the injector as well as experimentally measured pressure coefficient profiles along the combustor wall. It is shown that a thicker boundary layer will promote combustion but that heating the gas near the walls through a leading edge shock is more effective for ignition. However, the shocks generated by the leading edge may also influence the core flow of the constant area combustor and possibly cause some main stream mixing

Comparison of drag measurements of two axisymmetric scramjet models at Mach 6

Axial forces on quasi-axisymmetric scramjet models designed for operation at Mach 6 and Mach 8 were measured in the T4 Stalker tube at The University of Queensland using a single component stress wave force balance. A Mach 6 nozzle was used. The nozzle supply enthalpy was varied from 3 to 9 MJ/kg and the nozzle supply pressure from 35 to 45 MPa. As the conditions varied, the Mach number varied from 5.7 to 6.7. For both test models, the drag coefficients decreased with increasing Mach number. However, significant differences between the models were not observed over a range of free stream Mach numbers. A theoretical procedure to calculate the drag coefficient was found to give good agreement with experiments when appropriate account was taken of flow spillage at the intake

Children with complex support needs in healthcare settings for prolonged periods: their numbers, characteristics and experiences

This report details the findings of research conducted in England and Scotland to identify how many children with complex support needs are spending longer than one month in healthcare settings in Scotland and England, how and why they are in hospital, why they have not been discharged home or to appropriate alternative community-based facilities, and how well the hospital or healthcare setting is meeting their emotional, social and educational needs. It finds that many of these children could and should be discharged but are not, for a variety of reasons: primarily the lack of appropriate resources in the community and poor discharge planning processes, coupled with the inability of their families to manage their care and supervision without intensive support. Hospitals and healthcare settings in many cases are not meeting their needs and these children are being denied the protection offered by UK legislation governing children's rights and welfare

Species measurements in a hypersonic, hydrogen-air, combustion wake

A continuously sampling, time-of-flight mass spectrometer has been used to measure relative species concentrations in a two-dimensional, hydrogen-air combustion wake at mainstream Mach numbers exceeding 5. The experiments, which were conducted in a free piston shock tunnel, yielded distributions of hydrogen, oxygen, nitrogen, water and nitric oxide at stagnation enthalpies ranging from 5.6 MJ kg(exp -1) to 1.2 MJ kg(exp -1) and at a distance of approximately 100 times the thickness of the initial hydrogen jet. The amount of hydrogen that was mixed in stoichiometric proportions was approximately independent of the stagnation enthalpy, in spite of the fact that the proportion of hydrogen in the wake increased with stagnation enthalpy. Roughly 50 percent of the mixed hydrogen underwent combustion at the highest enthalpy. The proportion of hydrogen reacting to water could be approximately predicted using reaction rates based on mainstream temperatures

Mass spectrometer measurements of test gas composition in a shock tunnel

Shock tunnels afford a means of generating hypersonic flow at high stagnation enthalpies, but they have the disadvantage that thermochemical effects make the composition of the test flow different to that of ambient air. The composition can be predicted by numerical calculations of the nozzle flow expansion, using simplified thermochemical models and, in the absence of experimental measurements, it has been necessary to accept the results given by these calculations. This note reports measurements of test gas composition, at stagnation enthalpies up to 12.5 MJ.kg(exp -1), taken with a time-of-flight mass spectrometer. Limited results have been obtained in previous measurements. These were taken at higher stagnation enthalpies, and used a quadruple mass spectrometer. The time-of-flight method was preferred here because it enabled a number of complete mass spectra to be obtained in each test, and because it gives good mass resolution over the range of interest with air (up to 50 a.m.a.)