bluuebunny/crossref_metadata_2025_split huggingface dataset:
Aircraft Behaviour in a Vertical Gradient of Wind Velocity
Authors: Zbrożek J. K. 
Published: July 2016

SummaryThe stability of the phugoid motion of an aircraft in the presence of wind shear is investigated. The effect of the wind shear on the phugoid frequency increases with increasing aircraft speed and can be stabilising or destabilising, depending on the aircraft orientation relative to the wind shear. The destabilising effect of wind shear is alleviated by the stabilising effect of the density gradient of the atmosphere. At the most critical combination of speed and altitude a strong wind shear may lead to divergence, with a time to double amplitude of the order of 10-15 seconds.A numerical study of the aircraft motion with controls fixed when descending through a wind profile similar to that in a jet stream indicates that the increase in the aircraft indicated speed can be of the same magnitude as, or larger than, the maximum wind velocity increment in the jet stream core. However, as the time to reach the excess speed is of the order of one minute, the actual behaviour of the aircraft strongly depends on the pilot's action and thus is not fully predictable by theoretical analysis.
The Effect of a Root Gap on the Aerodynamic Forces of a Slender Delta Wing in Oscillatory Pitching Motion
Authors: Judd M. 
Published: July 2016

SummaryAn investigation of the effect of a root gap is extended to the oscillatory pitching motion of a slender wing. Potential theory is used and the unsteady forces are shown to be reduced by the gap as drastically as the steady. These results cast doubt on measurements made by the technique of half-model testing. Viscous flow in the gap is discussed with reference to the possible types of model mount. The effect of viscosity may be to reduce the gap loss, but the extent of the improvement is uncertain.
Stresses Around a Reinforced Circular Hole Near a Reinforced Straight Edge
Authors: Davies G. A. O. 
Published: July 2016

SummaryA solution is presented for the stresses in a half plane compactly reinforced along its straight edge and pierced by a reinforced circular hole in the vicinity of the edge. Numerical results are given for two cases of uniform applied tractions at infinity. In the special case of both boundaries unreinforced, the results obtained are in agreement with an existing solution by Mindlin.
Influence of Stiffener Thickness and Rivet Position upon the Effectiveness of Single-Sided Stiffeners on Shear Webs
Authors: Rockey K. C. 
Published: July 2016

SummaryThe paper presents the results of an experimental study of the buckling of transversely stiffened shear webs when the stiffeners have a thickness less than that of the web-plate.It is shown that the effectiveness of such stiffeners is greatly influenced by two factors, the ratio of the thickness of the attached leg to that of the web-plate and the position of the connecting rivet. An empirical design rule relating these two factors is presented.
The Effect of Jet Entrainment on Lift and Moment for a Thin Aerofoil with Blowing
Authors: Wygnanski I . , Newman B. G. 
Published: July 2016

SummaryJet flap theory for thin aerofoils has been extended to include the effect of jet entrainment on the external flow when the jet is blown over the upper surface of the aerofoil. The effective camber of the aerofoil is increased by the sink effect due to entrainment and the increase of lift at zero incidence is proportional to the square root of the jet momentum coefficient. Formulae and charts are presented to facilitate the determination of the increments of lift and pitching moment due to this effect. The theory is shown to be in first-order agreement with the exact solution for a circular-arc aerofoil of small camber with distributed sinks on the upper surface.The new theory is compared with four old sets and one new set of experimental data. It greatly improves the accuracy of prediction for cases where the incidence and flap angle are small. The new theory substantiates the usefulness of a small flap in applications of the jet flap principle.
The Flow Induced by Two-Dimensional and Axisymmetric Turbulent Jets Issuing Normally from an Infinite Plane Surface
Authors: Wygnanski I. 
Published: July 2016

SummaryThe flows induced by incompressible jets have been analysed for two-dimensional and axisymmetric jets emerging at right angles from an infinite plane surface. In particular, the pressure distribution on the surface has been predicted by replacing the jet with a line sink of variable strength. The theory takes account of the size of the blowing slot or nozzle and is in good agreement with experiment in both cases.
Applications of Linearised Characteristics to Sharp-Edged Conical Bodies
Authors: Squire L. C. 
Published: July 2016

SummaryA review of existing work in the field of linearised characteristics suggests that the hypersonic approximation introduced by Chapkis should be adequate in many cases of practical interest; furthermore, of the methods available, this approximation requires least computation for the calculation of pressure distributions on a given shape at given speed. The application of this method to sharp-edged conical shapes shows good agreement with measured zero-incidence pressure distributions for a variety of shapes and a wide range of hypersonic parameter. The agreement is less good at incidence, possibly due to flow separations in the real flow.
On the Axisymmetrical Stress Concentration at an Eccentrically Reinforced Circular Hole in a Plate
Authors: Wittrick W. H. 
Published: July 2016

SummaryThis paper is concerned with the effectiveness of reinforcing a hole in a plate on one surface only. The particular problem considered is that of a circular hole in a plate of infinite extent, subjected to axially symmetrical tension at infinity, when the reinforcement consists of an annular plate on one surface. Because of the interaction between bending and stretching, the problem is highly non-linear and it has only been possible to solve it for certain limiting cases. The stress concentration factor depends on a dimensionless parameter proportional to the tension at infinity. It is shown that the stress concentration factor is increased, because of the eccentricity of the reinforcement, if the parameter is small, but for values of the parameter greater than a certain minimum the stress concentration factor is decreased. The results also make it quite clear that there is no possibility of obtaining reasonably accurate results by linearisation of the equations.
The Three-Shock Confluence on a Simple Wedge Intake
Authors: Henderson L. F. 
Published: July 2016

SummaryResults obtained from previous studies of the three-shock confluence are applied to a simple wedge intake with the objective of obtaining a qualitative description of the flow for given initial conditions (M0, δ0). A simple mapping procedure is used, so that when M0, δ0 varies slowly and continuously the resulting effect on the shock geometry can be discussed in a systematic fashion. A number of special curves are computed to help classify various regions of initial conditions.
Shear Buckling of Clamped Infinitely Long Plates—Influence of Torsional Rigidity of Transverse Stiffeners
Authors: Rockey K. C. , Cook I. T. 
Published: July 2016

SummaryThe paper provides relationships between the buckling resistance of clamped transversely stiffened plates and the flexural rigidity of the stiffeners for various values of the ratio of torsional rigidity to flexural rigidity. Results are presented for four different stiffener spacings.
Design of Two-Dimensional Free Streamline Suction Slots for Parallel Channels
Authors: Lau W. T. F. 
Published: July 2016

SummaryA general solution is obtained by using potential flow theory for the design of two-dimensional suction slots for parallel channels. These slots are formed by free streamlines and are so arranged that the channel walls are free from adverse pressure gradient. Where suction slots are intended for the control of boundary layers, the present solution can only be used as a basis for experiment. It is interesting to note that the results also suggest a new method for the design of diffusers by suction.
The Use of Excess Engine Exit Area Over Intake Area to Reduce Zero-Lift Drag at High Supersonic Speeds
Authors: Squire L. C. 
Published: July 2016

SummaryAt flight speeds above about M=2 the cross-sectional area of the fully-expanded jet nozzle tends to be larger than the intake streamtube. The principle of integrating this increase in area of the propulsion unit with the usable volume in order to reduce the after-body drag of the combination is discussed and calculations are made to establish the order of the effect. It is deduced that successful integration of this type can produce worthwhile increases in lift/drag ratio.
The Increase of Ablation Effectiveness by Surface-Active Compounds
Authors: Steverding B. 
Published: July 2016

SummaryThe heat of ablation of glassy materials can be improved by surface-active agents. The degree of improvement is more pronounced at high flight velocities and depends strongly on the coefficient of diffusion in the liquid layer. The analysis is carried out near the stagnation point of blunt bodies for steady state ablation.
The Growth of a Vortex in Turbulent Flow
Authors: Squire H. B. 
Published: July 2016

SummaryThe growth of a line vortex with time and the spread of a trailing vortex behind a wing due to turbulence are considered. It is shown that the eddy viscosity for this type of motion may be taken to be proportional to the circulation round the vortex and the solution is then similar to the solution for the growth of a vortex in laminar flow. The method is applied to calculate the distance behind a wing for which the trailing vortices will touch one another.
A Large Scale Fatigue Test of Aluminium Specimens
Authors: Bloomer N. T. , Roylance T. F. 
Published: July 2016

SummaryThere have been, in the past, many fatigue tests carried out on a variety of materials and components. These all indicate a wide scattering in the lives (measured by the number of stress cycles to failure) endured by nominally identical components subjected to nominally identical forces before failure occurs. To interpet this scattering several equations have been suggested as representing the statistical distribution functions that fit the lives obtained for individual types of component. Of these functions the log normal distribution function has been perhaps the most widely used. For the central regions of the probability distribution, i.e. about the mean, the log normal distribution and several others represent experimental results very closely indeed, but engineers and designers of all kinds dare not design on the mean fatigue life. They are concerned with specifications that either exclude the possibility of failure or admit only a very small probability of failure. It is thus with the accuracy with which the “lower tail” of the probability distribution curve fits the experimental results that they are concerned.To assess the fit at this lower end for one type of component, a large number (about 1,000) of aluminium specimens have been tested and the corresponding lives plotted. The results are very interesting. They show clearly that the log normal distribution for this type of component and material is pessimistic for a probability of failure of less than 0·3. This result is felt by the authors to be of very great importance. It has further been shown that the use of the “one-sided censored distribution function”, used previously by one of the authors, gives a curve that will fit the lower results better than the complete log normal distribution would do.It is with the testing procedure adopted, the specimens used, the distribution functions considered and the conclusions obtained therefrom that this paper is concerned.
The Effect of a Rear-Mounted Disc on the Drag of a Blunt-Based Body of Revolution
Authors: Mair W. A. 
Published: July 2016

SummaryExperiments have shown that the drag of a body of revolution with a blunt base can be substantially reduced by mounting behind the body a disc of rather smaller diameter than the body. With a single disc the base drag was reduced by about 35 per cent and with two discs a reduction of 55 per cent was obtained. When the cavity between the body and the best single disc was filled in to form a solid boat-tailed afterbody there was an even greater reduction of drag.A single disc mounted nearer to the body than the position giving low drag gave a large increase of drag with severely unsteady flow. The nature of the flow in both the low-drag and high-drag régimes is discussed.
On the Piston Motion of a Free-Piston Shock Tube
Authors: Peng Tzy C. , Elbert Theo. F. 
Published: July 2016

SummaryThe motion of a solid piston between the driver and test gases in a closed shock tube is studied. In particular, the piston stopping distance, i.e. the total length required to bring the piston to a stop, is calculated for various experimental conditions. Before the stop, the moving piston compresses the test gas, at first with its induced shock and then further with its own kinetic energy through the successive shock reflections. Thus, the moving piston can produce a reservoir of compressed gas with higher enthalpy than a shock of similar strength without the piston. Normal shock-wave theory for an ideal gas is used until the first reflected shock meets the piston. The subsequent shock reflections are approximated by a continuous compression in thermodynamic equilibrium. The calculated values for the piston stopping distance are found to compare favourably with the available experimental data, indicating that the approximations used are reasonable. Peak pressure and temperature of the compressed test gas are computed, and the effect of bleeding the gas reservoir through a nozzle is also included.
Effects of a Source-Type Hypersonic Free Stream on the Flow Field about an Axisymmetric Cone
Authors: Savage Stuart B. 
Published: July 2016

SummaryMost hypervelocity tunnels presently make use of conical or wedge type nozzles which produce source-type flow non-uniformities in the test section. The present paper considers the effects of such free-stream non-uniformities on the flow fields about slender axisymmetric cones. The inviscid flow is considered within the framework of the Newtonian expansion procedure of Cole and simple expressions are obtained for the flow field properties in the shock layer. This inviscid analysis predicts that a free-stream gradient of a magnitude typical of present hypervelocity test facilities can cause sizeable reductions in surface pressure and increased shock-layer thickness at the aft end of long slender conical models. The cone pressure, accounting for the viscous-inviscid interaction, is obtained by applying the inviscid analysis in tangent-cone fashion to the effective body (i.e. physical cone plus boundary-layer displacement thickness). Cheng’s simple equation is used to approximate the hypersonic boundary-layer development. Large increases in the boundary-layer thickness at the aft end of the model are predicted as a consequence of the source flow effects. The analyses agree well with experimental measurements of surface pressure and boundary-layer thickness made on a 5° half-angle cone tested in the Republic 24 inch Longshot I hypervelocity shock tunnel.
Forced Autorotat ion in the Rolling Motion of an Aeroplane
Authors: Walsh G. R. 
Published: July 2016

SummaryThe possible steady rates of roll of an aeroplane are determined in the case when inertia cross-coupling is present. This phenomenon not only changes the simple linear relationship between aileron angle and rate of roll, but may lead to more than one possible rate of roll for a given aileron angle. Simplified equations of motion are given for the cases in which the rolling takes place (a) from level flight, (b) during a pull-out manoeuvre. In both cases, these equations, which are non-linear, are solved numerically for typical examples. The static stability of the possible steady motions is considered in detail, and the dynamic stability is determined in the numerical examples.
Oscillating Slender Wings with Leading-Edge Separation
Authors: Randall D. G. 
Published: July 2016

SummaryA theoretical study is made of the aerodynamics of wings executing simple harmonic oscillations. The wings considered are slender and infinite-simally thin; they may have curved leading edges and be cambered, but their cross sections must be straight lines. The value of the reduced frequency is assumed to be such that the flow is governed by the two-dimensional Laplace equation.Leading-edge separation is simulated by a line vortex joined to the leading edge by a cut. The strength and position of the vortex and the values of the generalised forces can be determined by the theory. Results have been calculated for flat delta wings and a flat gothic wing; they are in reasonable agreement with experiment.
The Nature of the Free-Stream Conditions Approaching an Oscillating Body in a Low Speed Wind Tunnel
Authors: Roberts B. W. 
Published: July 2016

SummaryWhen correcting the measured unsteady aerodynamic forces experienced by an oscillating body for wind-tunnel interference, it is customary to assume that the free-stream conditions ahead of the model are invariant with time. For small, streamlined models oscillating with small amplitudes this assumption is substantially correct. However, for large variations in the drag force on the oscillating body this assumption is imprecise, particularly at low frequency parameters. In the present paper the flow at stations a long way removed from the body section is examined on the basis of the unsteady form of the Bernoulli equation. The predicted free-stream fluctuations are found to be in agreement with experiment.
Roll Control Techniques on Magnetic Suspension Systems
Authors: Goodyer M. J. 
Published: July 2016

SummaryThe various methods which axe available for controlling the rolling motions of a model suspended in an electro-magnet system are discussed. Data on the moment capability and damping achieved with some of the possible control techniques are presented, together with details of the roll control system adopted for the six-component magnetic balance which has been developed at Southampton University for an 8 in × 6 in supersonic wind tunnel.
Plate-Reinforced Holes
Authors: Davies G. A. O. 
Published: July 2016

SummaryThe problem considered is the theoretical analysis and design of reinforcement around holes in plane sheets subjected to prescribed stresses at infinity. The reinforcement is taken to be an extensive thin plate attached to the sheet rather than the usual “compact bead” placed around the inside of the hole. The optimum design of the hole and the reinforcement is treated in two ways, firstly as an attempt to produce a “neutral hole” and secondly, to achieve the smallest stress concentration with the minimum amount of reinforcement. It is found in two cases that the plate-reinforcement can be as efficient as the bead but that, for both types, the validity of the theory is doubtful just when they are most efficient.
Similar and Asymptotic Solutions of the Incompressible Laminar Boundary Layer Equations with Suction
Authors: Zamir M. , Young A. D. 
Published: July 2016

SummarySimilar solutions of the boundary layer equations for incompressible flow with external velocity u1 ∞ xm and suction velocity υw ∞ x(m-1)/2 are obtained for negative values of m, in the range −0-1 to −0-9, and a wide range of suction quantities.The results are used, in combination with, existing solutions for positive m, to provide a guide to the ranges of m and suction parameter [(υw/u1√x] for which a general form of the classical asymptotic solution can be regarded as a good approximation to the exact solution.It is shown that the values of both m and suction parameter are generally important in this comparison, but for values of the latter greater than about 8 the approximation is a very good one for all values of m considered. For m≃−0·14 the approximation is good (i.e. the error is less than about 1 per cent) down to values of the suction parameter as low as 1·0.
The Calculation of Three-Dimensional Turbulent Boundary Layers: Part II: Attachment-Line Flow on an Infinite Swept Wing
Authors: Cumpsty N. A. , Head M. R. 
Published: July 2016

SummaryAn earlier paper described a method of calculating the turbulent boundary layer flow over the rear of an infinite swept wing. It made use of an entrainment equation and momentum integral equations in streamwise and cross-flow directions, together with several auxiliary assumptions. Here the method is adapted to the calculation of the turbulent boundary layer flow along the attachment line of an infinite swept wing. In this case the cross-flow momentum integral equation reduces to the identity 0 = 0 and must be replaced by its differentiated form. Two alternative approaches are also adopted and give very similar results, in good agreement with the limited experimental data available. It is found that results can be expressed as functions of a single parameter C*, which is evidently the criterion of similarity for attachment-line flows.
Transitional and Turbulent Boundary Layers on a Cold Flat Plate in Hypersonic Flow
Authors: Richards Bryan E. 
Published: July 2016

SummaryAn experimental investigation of natural transition and turbulent boundary layers on a cold flat plate in hypersonic flow was carried out in the Imperial College Gun Tunnel. Studies were also made of the effects of both two- and three-dimensional roughness elements including vortex generators.Results indicate that the Reynolds number based on the end of transition consists of two separate parts. These are the Reynolds numbers based respectively on the position of the apparent origin of the transition region behaviour, Ri, and on the length of the transition region measured from this origin. Ri is shown to be independent of unit Reynolds number for a sharp leading-edge model, and by correlations of other published data to vary little with Mach number. This origin is perhaps the most relevant point when comparisons are made between experiment and classical stability theory. The variation of the heat transfer rate during the transition region is compared with findings at low speed and shown to be similar to that expected from the turbulent spot concept of Emmons. The measured variation of the length of the transition region (x) from this origin gives an explanation for the unit Reynolds number effect on transition, and the rapid increase of transition Reynolds number with Mach number in hypersonic flow. The effect of bluntness on these factors is discussed.The virtual origin of the turbulent boundary layer is shown to lie close to the measured beginning of transition. At these high Mach number and low wall temperature conditions experimental values of heat transfer and values of skin friction coefficient derived from the estimated momentum thickness growth in the turbulent region are found to be appreciably higher than predictions by present theories.Roughness trips were found to bring the whole transition region forward. Only small differences in the measured boundary layer thickness, shape and heat transfer rates in the turbulent region (referenced to the estimated virtual origin in each case) were found after natural and forced transition. The transition point locations on a flat plate with either spherical roughness elements or vortex generators were found to agree with values predicted by the method of Potter and Whitfield as modified by Luxton to account for the effects of heat transfer.