Showing papers by "Vaughn College of Aeronautics and Technology published in 1969"

Electrical Resistance of Single Carbon Fibres

Abstract: SINGLE carbon fibres 25 cm long have been strained at a rate of 0.1 cm/h and their electrical resistance monitored continuously. Three different grades of fibre, each from a different source, have been studied (Table 1); values of Young's modulus were determined from tensile tests on individual fibres. The electrical resistance of the unstrained fibres varied from fibre to fibre even among fibres of the same grade. The variations within the grades appeared to be due to variations in the diameter of the fibres; mean values of resistance and diameter are given in Table 1.

An Improved Procedure for Orthogonalising the Search Vectors in Rosenbrock's and Swann's Direct Search Optimisation Methods

Abstract: In the methods described by Rosenbrock (1960) and Swann (1964) for direct search optimisation of a function of n variables, local minima or maxima are sought by conducting univariate searches parallel to each of the n orthogonal unit vectors £J, \\\\, . . ., £° in turn, the distances moved in these directions being du d2,. . ., dn respectively. The set of n such searches constitutes one 'stage' of the calculation. For the next stage, subject to certain restrictions which need not be considered here, a new set of n orthogonal unit vectors £[, £\\, . . ., £\\ is generated, such that |J lies along the direction of greatest advance for the previous stage, i.e. along the line joining the first and last points of that stage in w-dimensional space. For this purpose, Rosenbrock proposed (and Swann also used) the following calculating sequence:

Reaction-Broadening in a Hydrogen-Oxygen Diffusion Flame

Abstract: The present paper is a continuation of the study of diffusion flames in a hydrogen-oxygen mixture which began with an investigation of equilibrium-broadening by the writer (1968). In the present model the hydrogen dissociation reaction is assumed to be so slow that it can be neglected. The effect of the remaining reaction rates on flame structure is then investigated by the method of matched asymptotic expansions, which provides information about the orders of magnitude of the various species' concentrations, and identifies simplified sets of equations which govern behaviour in various regions of the flame. The general forms of the solutions are established; attention is confined to analytical questions.

Radiation from flames in gas turbines and rocket engines

Abstract: A brief description of the nature of flame radiation in gas-turbine combustors is followed by a discussion on the use and limitations of existing methods for estimating luminous emissivity. Since it is generally agreed that luminous radiation emanates from soot particles in the flame, consideration is given to the process of soot formation and to the influence of chemical composition on the soot-forming tendencies of fuels. Experimental data on the effects on flame radiation of variations in the operating conditions of pressure, temperature, velocity, and fuel-air ratio are presented and discussed. The important influence on radiation of the distribution of air and fuel in the combustion zone is also considered. In rocket engines, problems of radiation are less important because radiation normally respresents only a small fraction of the total heat transferred to the walls. For this reason, interest in radiation in rocket engines has so far centered mainly on the exhaust gases, and flame radiation has received comparatively little attention. The small amount of available experimental data is reviewed and attention is drawn to the need for further work to clarity one or two existing anomalies.

A study of free-jet and enclosed supersonic diffusion flames

Abstract: An experimental study has been made of supersonic diffusion flames produced by the subsonic and supersonic free-jet injection of hydrogen into a high-enthalpy air-stream. The air-stream was flowing at a Mach number=1.98 and had a total temperature of approximately 1900°K and a static pressure of 14.7 psia. An axial, mid-stream mode of fuel injection was adopted. For the case of hydrogen injected subsonically, combustion was found to be complete (i.e. the concentration of unreacted hydrogen was negligible), at a distance of approximately 9 inches from the point of injection. For the supersonic injection of hydrogen this distance was increased by approximately 30%, for the range of fuel velocities used. The tests were repeated with methane as the injected fuel, but ignition did not occur even with the methane preheated to 480°K, or when a bluff-body was inserted into the flow to create shock conditions. The above flames were then enclosed in various combustors of simple geometry, either of constant-area, constant-divergence or some combination of these two. For the conditions specified above, combustion in the diffusional mode was found to be impossible in a constantarea combustor. A diffusion flame was initiated in a combustor which consisted of a short parallel section followed by a section with a divergence of approximately 1°. However no combustion took place within a completely divergent duct even though the divergence was less than 1°. An exponential relationship between pressure, area and length has been proposed, and a one-dimensional analytical treatment for the case of heat addition in a non-constant-area duct is included in this paper. This assumption is shown to be experimentally reasonable and to result in gas dynamic equations which include the effect of process length.

The effect of the large hydrogen dissociation activation energy on an equilibrium-broadened hydrogen-oxygen diffusion flame

Abstract: The structure of a hydrogen-oxygen diffusion flame under equilibrium conditions is dominated by the influence of the equilibrium constant for the hydrogen dissociation-recombination reaction. An attempt to continue a previous solution, which used the method of matched asymptotic expansions, to higher orders of approximation led to difficulties of a numerical kind as a result of the large rate-of-change of this equilibrium constant with temperature. It is shown how the matter can be resolved by using the asymptotic expansion method with the small parameter (reciprocal of the equilibrium constant) treated as a function of temperature; the solutions follow from a simple iterative procedure.

Eddy-current testing at microwave frequencies

Abstract: This paper describes a microwave eddy-current apparatus, working at 25, 000MHz, for investigating surface defects and thin metallic coatings On suitable materials the instrument could detect a 2% change in the resistivity of surface layers and coatings about 1 micron thick It has been applied to life tests on aluminized Nimonic 105

The Second Century Papers: Looking Ahead in Aeronautics—19: Air Traffic and Navigation in the Second Century

Abstract: Navigation has been defined as “the business of conducting a craft as it moves about its ways“. This broad definition of navigation encompasses the whole process of handling, steering, control, guidance and operation of the craft in a safe and economic manner. Navigation has a much longer history than aeronautics. As man first began to explore the world and to develop trade, the need for safe and predictable operation of the craft was a spur to the application of the most advanced science and technology of the day.