57,731 research outputs found
Design considerations for the airframe-integrated scramjet
Research programs at the NASA Langley Research Center on the development of airframe-integrated scramjet concepts (supersonic combustion ramjet) are reviewed briefly. The design and performance of a specific scramjet configuration are examined analytically by use of recently developed and substantiated techniques on boundary-layer development, heat transfer, fuel-air mixing, heat-release rates, and engine-cycle analysis. These studies indicate that the fixed-geometry scramjet module will provide practical levels of thrust performance with low cooling requirements. Areas which need particular emphasis in further development work are the combustor design for low speeds and the integrated nozzle design
Evaluation of a bulk calorimeter and heat balance for determination of supersonic combustor efficiency
Results are presented from the shakedown and evaluation test of a bulk calorimeter. The calorimeter is designed to quench the combustion at the exit of a direct-connect, hydrogen fueled, scramjet combustor model, and to provide the measurements necessary to perform an analysis of combustion efficiency. Results indicate that the calorimeter quenches reaction, that reasonable response times are obtained, and that the calculated combustion efficiency is repeatable within + or -3 percent and varies in a regular way with combustor model parameters such as injected fuel equivalence ratio
Exploratory tests of two strut fuel injectors for supersonic combustion
Results of supersonic mixing and combustion tests performed with two simple strut injector configurations, one with parallel injectors and one with perpendicular injectors, are presented and analyzed. Good agreement is obtained between static pressure measured on the duct wall downstream of the strut injectors and distributions obtained from one-dimensional calculations. Measured duct heat load agrees with results of the one-dimensional calculations for moderate amounts of reaction, but is underestimated when large separated regions occur near the injection location. For the parallel injection strut, good agreement is obtained between the shape of the injected fuel distribution inferred from gas sample measurements at the duct exit and the distribution calculated with a multiple-jet mixing theory. The overall fraction of injected fuel reacted in the multiple-jet calculation closely matches the amount of fuel reaction necessary to match static pressure with the one-dimensional calculation. Gas sample measurements with the perpendicular injection strut also give results consistent with the amount of fuel reaction in the one-dimensional calculation
Pure Anderson Motives and Abelian \tau-Sheaves
Pure t-motives were introduced by G. Anderson as higher dimensional
generalizations of Drinfeld modules, and as the appropriate analogs of abelian
varieties in the arithmetic of function fields. In order to construct moduli
spaces for pure t-motives the second author has previously introduced the
concept of abelian \tau-sheaf. In this article we clarify the relation between
pure t-motives and abelian \tau-sheaves. We obtain an equivalence of the
respective quasi-isogeny categories. Furthermore, we develop the elementary
theory of both structures regarding morphisms, isogenies, Tate modules, and
local shtukas. The later are the analogs of p-divisible groups.Comment: final version as it appears in Mathematische Zeitschrif
Experimental investigation of a swept-strut fuel-injector concept for scramjet application
Results are presented of an experiment to investigate the behavior at Mach 4 flight conditions of the swept-strut fuel-injector concept employed in the Langley integrated modular scramjet engine design. Autoignition of the hydrogen fuel was not achieved at stagnation temperatures corresponding to a flight Mach number of 4; however, once ignition was achieved, stable combustion was maintained. Pressure disturbances upstream of the injector location, which were caused by fuel injection and combustion, were generally not observed; this indicates the absence of serious adverse combustor-inlet interactions. Mixing performance and reaction performance determined from probe surveys and wall pressure data indicate that high combustion efficiency should be obtained with the combustor length provided in the scramjet engine design. No adverse interaction between the perpendicular and parallel fuel-injection modes was observed
Langley Mach 4 scramjet test facility
An engine test facility was constructed at the NASA Langley Research Center in support of a supersonic combustion ramjet (scramjet) technology development program. Hydrogen combustion in air with oxygen replenishment provides simulated air at Mach 4 flight velocity, pressure, and true total temperature for an altitude range from 57,000 to 86,000 feet. A facility nozzle with a 13 in square exit produces a Mach 3.5 free jet flow for engine propulsion tests. The facility is described and calibration results are presented which demonstrate the suitability of the test flow for conducting scramjet engine research
A theory of non-local linear drift wave transport
Transport events in turbulent tokamak plasmas often exhibit non-local or
non-diffusive action at a distance features that so far have eluded a
conclusive theoretical description. In this paper a theory of non-local
transport is investigated through a Fokker-Planck equation with fractional
velocity derivatives. A dispersion relation for density gradient driven linear
drift modes is derived including the effects of the fractional velocity
derivative in the Fokker-Planck equation. It is found that a small deviation (a
few percent) from the Maxwellian distribution function alters the dispersion
relation such that the growth rates are substantially increased and thereby may
cause enhanced levels of transport.Comment: 22 pages, 2 figures. Manuscript submitted to Physics of Plasma
Constraints and evolution in cosmology
We review some old and new results about strict and non strict hyperbolic
formulations of the Einstein equations.Comment: To appear in the proceedings of the first Aegean summer school in
General Relativity, S. Cotsakis ed. Springer Lecture Notes in Physic
Structural origins of the properties of rare earth nickelate superlattices
NiO6 octahedral tilts in the LaNiO3/SrTiO3 superlattices are quantified using
position averaged convergent beam electron diffraction in scanning transmission
electron microscopy. It is shown that maintaining oxygen octahedra connectivity
across the interface controls the octahedral tilts in the LaNiO3 layers, their
lattice parameters and their transport properties. Unlike films and layers that
are connected on one side to the substrate, subsequent LaNiO3 layers in the
superlattice exhibit a relaxation of octahedral tilts towards bulk values. This
relaxation is facilitated by correlated tilts in SrTiO3 layers and is
correlated with the conductivity enhancement of the LaNiO3 layers in the
superlattices relative to individual films.Comment: Accepted for publication in Physical Review B (Rapid Communication
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