Showing papers by "Vaughn College of Aeronautics and Technology published in 1967"

On the Flow Along Swept Leading Edges

Abstract: Flight tests on the Handley Page suction wing showed that turbulence at the wing root can propagate along the leading edge and cause the whole flow to be turbulent. The flow on the attachment line of a swept wing was studied in a low speed wind tunnel with particular reference to this problem of turbulent contamination. The critical Reynolds number, RθL , of the attachment-line boundary layer for the spanwise spread of turbulence was found to be about 100 for sweep angles in the range 40°–60°. A device was developed to act as a barrier to the turbulent root flow so that a clean laminar flow could exist outboard. This device was shown to be effective up to an Rθ of at least 170, so that experiments were possible on a laminar boundary layer at Reynolds numbers above the lower critical value. A spark was used to introduce spots of turbulence into the attachment-line boundary layer and the propagation speeds of the leading and trailing edges were measured. The spots expanded, the leading edge moving faster than the trailing edge, at high Reynolds numbers, and contracted at low values. The behaviour of Tollmien-Schlichting waves was also investigated by exciting the flow with sound emanating from a small hole on the attachment line. Measurements of the perturbation phase and amplitude were made downstream of the source and, although accurate values of wave length and propagation speed could be found, difficulties were experienced in evaluating the amplification ratio. Nevertheless, all small disturbances decayed at a sufficient distance from the source hole up to the highest available Reynolds number of 170.

Further aspects of the thermal degradation of epoxide resins

Abstract: This paper describes an investigation into the degradation of a purified epoxide based on the diglycidyl ether of bisphenol A hardened with p,p′-diaminodiphenylmethane. The method used was that of hot-wire pyrolysis followed by gas chromatography. Special attention was given to the problem of solid residues formed on the pyrolyzer tube, and evidence was found that these probably contain oligomers. Resonance-stabilized free radicals also appear to be formed, and evidence is found to support the idea of dehydration during degradation, originally put forward by Lee. An attempt, based on first principles, is made to explain the degradation of epoxides, using evidence from previous work as well as that described in this paper.

The reflexion of a plane shockwave from a heat-conducting wall

Abstract: The situation following reflexion of a discontinuous plane shockwave from a coplanar, heat-conducting wall is analysed by the method of matched asymptotic expansions. Temperature jump effects are included. Two terms of the outer expansion are calculated ((i) the 'ideal' inviscid, nonheat conducting solution; (ii) the displacement effect) as well as two terms of the inner series ((i) constant pressure thermal boundary layer; (ii) first correction term resulting from pressure and temperature changes due to the displacement effect). The results agree reasonably well with experimental observations and it appears that accommodation effects may account for some observations of reflected-shock trajectories.

The Laminar Diffusion Flame in Oseen Flow: The Stoichiometric Burke-Schumann Flame and Frozen Flow

Abstract: The Oseen approximation is used to study the behaviour of two initially separated gas streams which, when they are united, may form a combustible mixture. The limiting cases of small and large burning reaction time are dealt with for an irreversible fuel-oxidant chemical reaction, the former of these cases being identified with the Burke-Schumann flame. The half-plane problems encountered lead to integral equations of the Wiener-Hopf type. Their general solutions are obtained and yield a description of the field near to the flame or mixing zone in terms of simple functions. We consider the following problem. Two uniform parallel gas streams in a two dimensional (planar) steady flow field are initially separated by a thin diaphragm lying along the negative half of the x axis. The chemical composition of the stream in the half-plane y > 0 is initially different from that in y < 0 but each stream is of such a character that downstream of x = 0, where they are allowed to unite, they may together form a combustible mixture. We wish to examine the disturbances created by the mixing and burning process, with the overriding assumption that the entire flow field is laminar. In order to accomplish this in a unified way we shall adopt the Oseen approximation (which linearizes the convective terms in the conservative equations), and will therefore follow Lagerstrom, Cole & Trilling (I949) and Laurmann (I958, I96I). The first group of authors used this method to elucidate the behaviour of a compressible, viscous, non-heat-conducting fluid. Laurmann included the effects of heat conduction and considered slip flows past finite and infinite flat plates. We generalize the basic sets of equations used by these authors to include the effects of variable chemical composition and its consequences. Apart from the Oseen-type of treatment which is to be used here, other, similar but not identical, studies have been undertaken previously. Closest in character to the present work is that carried out by Lilian (I963), who has dealt with comparable configurations with the aid of laminar boundary layer theory. Much of Linian's effort is directed towards an attempt to explain ignition and extinction phenomena. This will not be our immediate concern; rather do we propose to analyse one special configuration in a fairly detailed way. It is worth pointing out too that Lilian's work is applicable to high Reynolds number situations whereas the present approach, aside from any benefits which it may bring in the way of a unified treatment of the field, is especially applicable at low Reynolds numbers. As will be seen, this may well be of some importance in any subsequent discussions of extinction phenomena.

The variation of cycle times with repetition for manual tasks.

Abstract: The variation of cycle time with repetition has engaged the interest of ergonomists, psychologists, statisticians and engineers. The approach most directly useful to industrial management is that which enables time standards to be set more accurately, and which provides a basis for planning and estimating. The original relationships in aircraft manufacture have been found to be very useful for planning and estimating purposes, but are not sufficiently accurate for setting time standards for incentive schemes. It is in this field of time standards that a knowledge of accurate relationships could have a tremendous impact on direct labour costs. Furthermore, it could change fundamentally the existing practices for human work measurement Laboratory experiments to investigate a possible fundamental relationship applicable to all manual operations with varying degrees of skill and cycle time were conducted, Skilled and unskilled subjects performed operations requiring varying degrees of skill and cycle time. In...

Use of the Least Squares Line and Plane in the Measurement of Straightness and Flatness

Abstract: The paper deals with tabular methods for calculating the least squares line and the least squares plane with respect to which errors in straightness and flatness may be defined.

An experiment in stress redistribution caused by creep

Abstract: A simple redundant structure subjected to a non-uniform temperature distribution is simulated experimentally by means of two tensile-creep test machines holding specimens of Nimonic Alloy 90 at different temperatures in the range 800-900°C The machines are linked together so that although the total load applied to the specimens is constant the share of that load taken by each varies owing to dissimilar creep rates, as it would in the structure This redistribution of load is observed for several initial stress conditions and several temperature differences In each case the results are compared with calculations based on creep-strain data obtained from constant-stress tests An important practical feature of the results is the establishment of stable (fully redistributed) stresses These stresses are insensitive to the initial conditions, can be estimated quite simply from constant-stress creep data, and are always more uniform than the thermal stresses appropriate to the same temperature differe

Evaluation of Human Operator Coupled Dynamic Systems

Abstract: (1967). Evaluation of Human Operator Coupled Dynamic Systems. Ergonomics: Vol. 10, No. 2, pp. 125-138.

Engineering with Polymeric Materials

Abstract: Summary The rapid expansion of plastics and other polymeric materials into the general consumer market over the last few years is now being followed by an increasing use of these materials in more severe engineering applications. It is becoming necessary therefore for engineers to develop a familiarity with these materials commensurate with that which they already have for more conventional engineering materials. In many ways the physical properties of polymeric materials are highly complex and their description and relation to structure present real problems. This article presents, in a simple way, some of the background to our current level of understanding of the relation between structure and mechanical properties; gives some examples of how polymeric materials are being used; and discusses some of the problems of designing in these materials, which present a real challenge to both the physicist and the engineer.

Paper 22: Soft-Metal Bearings

Abstract: The rapid increase in the use of aluminium-alloy bearings is the most important development in soft-metal bearings over the last ten years. The context of this development is outlined, and reference made to other developments of high potential, notably oxide dispersion hardened tin, and metal-plastic composites.