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

Sharp bounds on 2m/r for static spherical objects

Sharp bounds are obtained, under a variety of assumptions on the eigenvalues of the Einstein tensor, for the ratio of the Hawking mass to the areal radius in static, spherically symmetric space-times.Comment: We changed a footnote in which an earlier result of H\aa{}kan Andr\'{e}asson was not described correctl

Shock Tunnel Studies of Scramjet Phenomena 1994

Reports by the research staff and graduate students of the Mechanical Engineering Department at the University of Queensland are collected and presented. These reports cover various studies related to the advancement of scramjet technology and the operation of advanced hypervelocity shock-expansion tubes. The report topics include the experimental studies of mixing and combustion in a scramjet flow path, the measurement of integrated thrust and skin friction, and the development of a free-piston-driven expansion tunnel capable of delivering a test gas at superorbital velocities

Shock tunnel studies of scramjet phenomena

Commissioning of the new T4 shock tunnel at the University of Queensland implied that it was no longer necessary to focus the work of the research group about an annual test series conducted in the T3 shock tunnel in Canberra. Therefore, it has been possible to organize a group for work to proceed along lines such that particular personnel are associated with particular project areas. The format of this report consists of a series of reports on specific project areas, with a brief general introduction commenting on each report. The introduction is structured by project areas, with the title of the relevant report stated under the project area heading. The reports themselves follow in the order of the project area headings

Musculoskeletal Modeling Component of the NASA Digital Astronaut Project

The NASA Digital Astronaut Project s (DAP) objective is to provide computational tools that support research of the physiological response to low gravity environments and analyses of how changes cause health and safety risks to the astronauts and to the success of the mission. The spaceflight risk associated with muscle atrophy is impaired performance due to reduced muscle mass, strength and endurance. Risks of early onset of osteoporosis and bone fracture are among the spaceflight risks associated with loss of bone mineral density. METHODS: Tools under development include a neuromuscular model, a biomechanical model and a bone remodeling model. The neuromuscular model will include models of neuromuscular drive, muscle atrophy, fiber morphology and metabolic processes as a function of time in space. Human movement will be modeled with the biomechanical model, using muscle and bone model parameters at various states. The bone remodeling model will allow analysis of bone turnover, loss and adaptation. A comprehensive trade study was completed to identify the current state of the art in musculoskeletal modeling. The DAP musculoskeletal models will be developed using a combination of existing commercial software and academic research codes identified in the study, which will be modified for use in human spaceflight research. These individual models are highly dependent upon each other and will be integrated together once they reach sufficient levels of maturity. ANALYSES: The analyses performed with these models will include comparison of different countermeasure exercises for optimizing effectiveness and comparison of task requirements and the state of strength and endurance of a crew member at a particular time in a mission. DISCUSSION: The DAP musculoskeletal model has the potential to complement research conducted on spaceflight induced changes to the musculoskeletal system. It can help with hypothesis formation, identification of causative mechanisms and supplementing small data samples

Scramjets and Shock Tunnels: The Queensland Experience

This article reports on the use of a shock tunnel to study the operation of scramjet powered configurations at sub-orbital velocities above 2 km/s. Thrust, as given by a net thrust equation, is used as a figure of merit throughout the study. After a short description of the shock tunnel used and its operating characteristics, experiments on the combustion release of heat in a constant area duct with hydrogen fuel are reviewed. The interaction between heat release in the combustion wake and the walls of the duct produced pressure distributions which followed a binary scaling law, and indicated that the theoretically expected heat release could be realized in practice, albeit with high pressure or long combustion ducts. This heat release, combined with attainable thrust nozzle characteristics and a modest level of configuration drag, indicated that positive thrust levels could be obtained well into the sub-orbital range of velocities. Development of a stress wave force balance for use in shock tunnels allowed the net thrust generated to be measured for integrated scramjet configurations and, although the combination of model size and shock tunnel operating pressure prevented complete combustion of hydrogen, the cruise condition of zero net thrust was achieved at 2.5 km/s with one configuration, while net thrust was produced with another configuration using an ignition promoter in hydrogen fuel. Nevertheless, the combination of boundary layer separation induced inlet choking and limited operating pressure levels prevented realization of the thrust potential of the fuel. This problem may be alleviated by recent increases in the shock tunnel operating pressures, and by promising research involving inlet injection of the fuel. Research on the drag component of the net thrust equation resulted from the development of a fast response skin friction gauge. It was found that existing theories of turbulent boundary skin friction predicted the skin friction when combustion of hydrogen occurred outside the boundary layer, but combustion within the boundary layer dramatically reduced the skin friction. Finally, for the first time in the world, supersonic combustion was produced in a free flight experiment. This experiment validated shock tunnel results at stagnation enthalpies near 3 MJ/k

Shock tunnel studies of scramjet phenomena, supplement 5

A series of reports are presented on SCRAMjet studies, shock tunnel studies, and expansion tube studies. The SCRAMjet studies include: (1) Investigation of a Supersonic Combustion Layer; (2) Wall Injected SCRAMjet Experiments; (3) Supersonic Combustion with Transvers, Circular, Wall Jets; (4) Dissociated Test Gas Effects on SCRAMjet Combustors; (5) Use of Silane as a Fuel Additive for Hypersonic Thrust Production, (6) Pressure-length Correlations in Supersonic Combustion; (7) Hot Hydrogen Injection Technique for Shock Tunnels; (8) Heat Release - Wave Interaction Phenomena in Hypersonic Flows; (9) A Study of the Wave Drag in Hypersonic SCRAMjets; (10) Parametric Study of Thrust Production in the Two Dimensional SCRAMjet; (11) The Design of a Mass Spectrometer for use in Hypersonic Impulse Facilities; and (12) Development of a Skin Friction Gauge for use in an Impulse Facility. The shock tunnel studies include: (1) Hypervelocity flow in Axisymmetric Nozzles; (2) Shock Tunnel Development; and (3) Real Gas Efects in Hypervelocity Flows over an Inclined Cone. The expansion tube studies include: (1) Investigation of Flow Characteristics in TQ Expansion Tube; and (2) Disturbances in the Driver Gas of a Shock Tube

An alternative well-posedness property and static spacetimes with naked singularities

In the first part of this paper, we show that the Cauchy problem for wave propagation in some static spacetimes presenting a singular time-like boundary is well posed, if we only demand the waves to have finite energy, although no boundary condition is required. This feature does not come from essential self-adjointness, which is false in these cases, but from a different phenomenon that we call the alternative well-posedness property, whose origin is due to the degeneracy of the metric components near the boundary. Beyond these examples, in the second part, we characterize the type of degeneracy which leads to this phenomenon.Comment: 34 pages, 3 figures. Accepted for publication in Class. Quantum Gra

Shock tunnel studies of scramjet phenomena, supplement 7

Reports by the staff of the University of Queensland on various research studies related to the advancement of scramjet technology are presented. These reports document the tests conducted in the reflected shock tunnel T4 and supporting research facilities that have been used to study the injection, mixing, and combustion of hydrogen fuel in generic scramjets at flow conditions typical of hypersonic flight. In addition, topics include the development of instrumentation and measurement technology, such as combustor wall shear and stream composition in pulse facilities, and numerical studies and analyses of the scramjet combustor process and the test facility operation. This research activity is Supplement 7 under NASA Grant NAGW-674