bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Numerical Study of Vortex Shedding From One and Two Circular Cylinders
Authors: Stansby P.K. 
Published: July 2016

SummaryA discrete-vortex representation of the wake of a circular cylinder, in which vortices are convected in a potential-flow calculation and maintain their identities unless they approach one another or a surface closely, predicts many of the unsteady flow features and is computationally more efficient than other schemes. The mean rate of shedding of vorticity is adjusted to be compatible with experiments at a high subcritical Reynolds number of 3 × 104 and the model gives reasonable predictions of separation, drag, lift, Strouhal number and vorticity loss in the formation region. The method is extended to accommodate a second cylinder and many of the surprising features which have been observed experimentally with two cylinders in a side-by-side arrangement are reproduced.
Comparisons Between Inverse Boundary-Layer Calculations and Detailed Measurements in Laminar Separated Flows
Authors: Horton H.P. 
Published: July 2016

SummaryA brief description is given of an accurate numerical method for the inverse calculation of both attached and separated laminar, two-dimensional, incompressible boundary-layers with prescribed displacement thickness. The method employs downstream-marching, using an approximation to the convection terms in the reverse-flow region to stabilise the computation. Results of three calculations made by this method, using measured distributions of displacement thickness as input, are presented and compared with the corresponding measured velocity profiles and distributions of external velocity. Very close agreement between theory and experiment is found in general, giving further evidence of the validity of the boundary-layer approximation in separated flows of limited extent.
An Integral Method for the Oscillating Turbulent Boundary Layer
Authors: Patel M.H. 
Published: July 2016

SummaryThe linearised time dependent momentum integral equation is used in conjunction with assumed velocity profiles and a quasi-static skin friction approximation to predict the turbulent boundary layer response to sinusoidal streamwise velocity fluctuations in the freestream. The mean zero pressure gradient case, corresponding to flat plate flow, is presented in detail and verified by comparison with experimental data and alternative calculations. The asymptotic turbulent boundary layer response to very high frequency perturbations is also derived. It is shown that a travelling wave component in the freestream, with its associated time dependent streamwise pressure gradient, has a dominant effect on the turbulent boundary layer response.
Skin Friction and Heat Transfer at an Infinite Swept Attachment Line
Authors: Poll D.I.A. 
Published: July 2016

SummarySimple, yet reasonably accurate, expressions have been developed for the prediction of skin friction and heat transfer coefficient at an infinite swept attachment line using the concepts of ‘reference temperature’ and ‘Reynolds analogy’. The formulae have then been used to investigate the effect of varying sweep angle with constant undisturbed free stream conditions in the limits of very low and very high Mach number.
The Stiffness of a Two-Cell Anisotropic Tube
Authors: Mansfield E.H. 
Published: July 2016

SummaryAn analysis is made of the general two-cell thin-walled cylindrical tube subjected to longitudinal tension, bending and torsion. The walls of the tube may be of fibre composite with an asymmetric lay-up resulting in a coupling between direct and shear stresses and strains. The two-cell tube differs from the single-cell tube in that the tension axis and the principal axes of bending are not necessarily aligned to the c.g. and the principal moments of inertia of the longitudinal stress bearing material.
An Investigation of the Swirl in an S-Duct
Authors: Guo R.W. , Seddon J. 
Published: July 2016

SummaryMeasurements are presented of the static pressure, total pressure, swirl and three-dimensional turbulence in the flow through an S-curved rectangular duct mounted in a wind tunnel at different incidences, yaw angles and mass flow ratios. The results show that at high incidence there is a large vortex around an area of flow separation after the first bend and a pair of contra-rotating vortices in the flow after the second bend. The distortion of total pressure at the exit of the S-duct is significantly high, and the corresponding three-dimensional turbulence is up to 16.7%. Appreciation of the existence of this type of flow is important in the field of air intake design for jet aircraft.
The Importance of Secondary Shedding in Two-Dimensional Wake Formation at Very High Reynolds Numbers
Authors: Stansby P.K. , Dixon A.G. 
Published: July 2016

SummaryUncertainties in the use of the discrete-vortex method in modelling the time development of the wake of a circular cylinder at very high Reynolds numbers are investigated. It is shown that simply introducing vorticity at generally accepted separation positions at a rate of ½Us2, Us being the velocity at separation, gives wholly unrealistic wake predictions. In the base region pressure fields occur which would promote separation in steady flow and so a first approximation for ‘secondary’ separation is incorporated into the model. This brings pressure distributions and vorticity structures at subcritical and supercritical Reynolds numbers into good agreement with experiment. The convection of the vortices is calculated using the cloud-in-cell technique and comparisons are made with direct summation methods.
The Effect of Nose Blunting on the Wave Drag of Ogive Forebodies
Authors: Partington R. , Baker T.J. 
Published: July 2016

SummaryA theoretical method is used to predict the surface pressure distribution and drag-rise characteristics of blunted ogive forebodies. The results confirm the observation that a moderate degree of nose blunting can reduce wave drag relative to that of a pointed body of the same fineness ratio. An analysis of the theoretical data provides a simple explanation of this phenomenon.
Calculation of the Pressure Distribution on a Right-Angled Wedge
Authors: Barnes F.H. , Grant I. 
Published: July 2016

SummaryA comparison is made between three models of the two-dimensional flow of an inviscid fluid over a bluff body. The models are the Roshko free-streamline model, the Parkinson and Jandali wake-source model and the Bearman and Fackrell vortex-lattice model. The models are used to predict the surface pressure distribution on the front face of a right-angled wedge for the two symmetrical positions of the wedge, and a comparison is made with the experimental results of Slater. A further comparison is then made of Slater’s results for the surface pressure distributions on a wedge of finite thickness with the distributions predicted by the vortex-lattice model, for the wedge at a number of angular positions to the flow.
Unsteady Newton-Busemamn Flow Theory Part III. Frequency Dependence and Indicial Response
Authors: Hui W.H. 
Published: July 2016

SummaryA complete unsteady Newton-Busemann flow theory, including centrifugal force corrections, was recently given by Hui and Tobak and successfully applied to study the dynamical stability of oscillating aerofoils (Part I) and bodies of revolution (Part II). The present paper extends these results, which are restricted to the first order in frequency, to general frequencies that may be applicable to flutter analysis as well. Furthermore, the new results are used to investigate the behaviour of the indicial response functions in unsteady flow at very high Mach numbers. In particular, it is found that for a family of body shapes in the Newtonian flow, including the cone, the wedge, the delta wing and slender aerofoils, the aerodynamic response to a step change in angle of attack or pitching velocity contains an impulse at the initial instant. This is followed by a rapid adjustment to the new steady-flow conditions, the adjustment time being equal to that required for a fluid particle to travel a distance of the body length. The impulse component appearing at the infinite Mach number limit (Newtonian flow) is in effect an apparent mass term, analogous to that which occurs initially in the aerodynamic indicial response at the zero Mach number limit (incompressible flow). In the latter case the initial impulse is followed by an asymptotic adjustment to the new steady-flow conditions, theoretically taking infinite time, in direct contrast to the rapid adjustment in Newtonian flow.
Concerning Dynamic Stall
Authors: Smith F.T. 
Published: July 2016

SummaryThe unsteady breakdown or stall of streamlined flow near the rounded leading edge of an aerofoil, as the small angle of attack is raised above its critical stall value, is studied theoretically for large Reynolds number motion. The unsteady developments take place first over a relatively slow time scale but then the corresponding solution breaks down with a singularity, forcing a switch to a faster and more nonlinear process. The latter involves a very pronounced local bulge appearing in the flow displacement, accompanied by reversed flow at the aerofoil surface, and comparisons with experimental observations of dynamic stall are noted.
Loads and Pressures Due to Underexpanded Jets Impinging on Wedges
Authors: Hunt B.L. 
Published: July 2016

SummaryLoads have been measured on wedges placed symmetrically in supersonic jets of air. The jets were created by a nozzle with a radially divergent exit section having a lip Mach number of 2.2. The underexpansion ratio was varied from 1 to 2.2 and the distance between the nozzle exit section and the wedge apex was varied from 0 to 2 nozzle exit diameters. All wedges had a base width equal to the nozzle exit diameter: their total included apex angles covered the range 30° to 180°. Pressures were measured on the front faces and the bases for three of the wedges, hence enabling individual contributions to the overall force to be evaluated. Overall loads were measured by means of strain-gauged supports for all six wedges. It was found that the overall load coefficient is only weakly dependent on underexpansion ratio and wedge location but depends strongly on wedge angle. The maximum load coefficient recorded corresponded to 73% of the jet momentum. The base pressures contribute up to 59% of the overall load on a 45° wedge but rather less for larger wedge angles.
The Shape-Factor Relationship for Turbulent Boundary Layers
Authors: Telbany M.M.M. El , Niknejad J. , Reynolds A.J. 
Published: July 2016

SummaryConsideration is given to the relationship H1 = f(H) linking the common shape factor H and the mass-flow shape parameter H1 which is used in entrainment models of boundary-layer development. A formula suggested by Green et al is found to be most nearly consistent with the measurements presented. However, a more exact prediction of H1 is obtained by introducing a factor involving the Reynolds number based on the local momentum thickness θ; thus H1 = f(H, Reθ). Predictions obtained by incorporating the appropriately modified entrainment equation into the well-known method of Green et al prove not to give an improved representation of the development of boundary layers studied experimentally by the authors and others. It is concluded that the modified formula for H1 is primarily useful in giving an improved specification of the overall boundary layer thickness δ = θ(H1 + H), and hence of other features of the developing profile.
The Synthesis of an Active Flutter Suppression Law Based on an Energy Criterion
Authors: Klein A.F. 
Published: July 2016

SummaryTheory and results are presented which show that it is questionable to base a flutter suppression law, synthesised in terms of an energy dissipation criterion, entirely on aerodynamic data. It is shown that aileron mass balance and aileron/jack impedance can adversely affect regions of stability which have been predicted using aerodynamic terms alone. Comments are also made which attempt to unify various cost functions which are used when either an energy dissipation or an energy dissipation and storage criterion is used in the formulation of flutter suppression laws.
On an Approximate Method of Calculating Pressures on Non-lifting Head Shapes at Supersonic Speeds
Authors: Zienkiewicz H. K. 
Published: July 2016

SummarySlender-body theory is used to derive the ogive of curvature approximation for very slender, pointed, convex head shapes at supersonic speeds. Results of application of this approximation, together with the λ-method for circular arc ogives, to a variety of non-slender head shapes show very good agreement with the method of characteristics, van Dyke's second-order theory and experiment. Good agreement with the method of characteristics and with experiment is obtained even in cases when the stagnation pressure losses across the nose shock wave are not negligible.
On the Unsteady Motion of a Slender Body through a Compressible Fluid
Authors: Fraenkel L. E. 
Published: July 2016

SummaryWard's slender-body theory is extended to examine the unsteady motion of a slender body through a fluid at rest. The cross-sectional area and shape of the body, its forward velocity and its lateral motion are all arbitrary functions of time, but are subject to the restrictions of small disturbances. The length of the body is fixed. An approximate velocity potential is obtained by the joint use of two integral transforms, and the accuracy of this potential is discussed in some detail. General expressions for the aerodynamic forces acting on the body are derived in terms of a co-ordinate system which moves forward with the body in the mean direction of motion, but is fixed laterally. These expressions are then transformed, for the particular case of an oscillating rigid body moving forward with variable velocity, to expressions in terms of co-ordinates referred to the body axes. (The former co-ordinate system makes possible a fairly compact general treatment, whereas the latter is more convenient if the solution of a particular rigid-body problem is required.) Finally, arguments are advanced to justify the application of the slender-body theory to wings of slender plan form whose trailing edges are perpendicular to the direction of motion, and results are given for an oscillating wing moving forward with variable velocity.
Supersonic Flow Past Slender Bodies With Discontinuous Profile Slope
Authors: Fraenkel L. E. , Portnoy H. 
Published: July 2016

SummaryWard’s slender-body theory is extended to derive first approximations to the external forces on slender bodies of general cross section with discontinuous profile slope. Two classes of body are considered: bodies whose profile (typified by the local radius) is continuous between the nose and base, and certain bodies whose profile is discontinuous, such as bodies with annular or side air intakes and wing-bodies on which the wing has an unswept leading edge. (Where air intakes are concerned, it is assumed that they are sharp-edged and that there is no “ spillage ” of the internal flow).The following conclusions apply to the former class of bodies. The variation of drag with Mach number is found to depend only on the discontinuities in the longitudinal rate of change of the cross-sectional area, and is thus independent of cross-sectional shape. The drag itself is unchanged if the direction of the flow is reversed. The expressions for lift and moment assume the same forms as for smooth pointed bodies, the lift depending only on conditions at the base of the body.The general theory is applied to winged bodies of revolution with an unswept wing leading edge: the results bear a marked resemblance to those obtained by Ward. The results for wings alone are seen to be applicable, with one modification, to subsonic as well as to supersonic speeds.
The Lift of Twisted and Cambered Wings in Supersonic Flow
Authors: Lance G. N. 
Published: July 2016

SummaryA generalised conical flow theory is used to deduce an integral equation relating the velocity potential on a delta wing (with subsonic leading edges) to the given downwash distribution over the wing. The complete solution of this integral equation is derived. This complete solution is composed of two parts, one being symmetric and the other anti-symmetric with respect to the span wise co-ordinate; each part represents a velocity potential. For example, if y is the spanwise co-ordinate and x is measured in the free stream direction, then a downwash of the form w= - α11 Ux|y| is symmetric and will give rise to a symmetric potential, whereas w= - α11 Ux|y| sgn y is anti-symmetric and gives rise to an anti-symmetric potential. The velocity potentials of such flows are given in the form of Tables for all downwashes up to and including homogenous cubics in the spanwise and streamwise co-ordinates. Table III gives similar formulae in the limiting case when the leading edges become transonic; these are compared with results given elsewhere and serve as a check on the results of Tables I and II.
The Effect of Sting Supports on the Base Pressure of a Blunt-Based Body in a Supersonic Stream
Authors: Donaldson I. S. 
Published: July 2016

SummaryExperiments have been made to find the effect of the ratio of sting to base diameter on the base pressure of an axially symmetric body at zero incidence in a supersonic stream. The Mach number of the flow was 1·994 and the model boundary layer was turbulent. The model used was a one inch diameter circular cylinder without boat-tailing. It passed through and was supported upstream of the nozzle throat. This method of support allowed measurements to be made in the important (and hitherto unexplored) case of zero sting diameter.As the sting to base diameter ratio was increased from 0 to 0·85, the base pressure decreased. The minimum value reached was approximately 0·8 of the value it would have at the base of a two-dimensional body with a similar ratio of boundary layer thickness to base height. The base pressure coefficient rose rapidly to zero as the ratio was further increased to unity.Under the conditions of the experiments, with a sting to base diameter ratio of 0·4 the base pressure coefficient differed from that without a sting by approximately ten per cent. With the more modest ratio of 0·2, the difference was approximately three per cent.
Effect of Yielding on the Fatigue Properties of Test Pieces Containing Stress Concentrations
Authors: Gunn K. 
Published: July 2016

SummaryA method of estimating the fatigue properties of notched test pieces when cyclic loads are applied in the presence of mean stresses is described. The method takes into account the local yielding which occurs near the base of the notch when the nominal stresses are sufficiently high. The general form of the predicted R/M diagrams closely resembles those obtained experimentally in previously published work.
Note on the Extension of Evvard’s Method to Wings with Subsonic Leading Edges Moving at Supersonic Speeds
Authors: Hancock G. J. 
Published: July 2016

SummaryEvvard’s technique is applied to the problem of a thin finite wing moving at a supersonic speed when the leading edge is subsonic. It is developed in two methods:—(i) in which the relationship between the pressure loading and the integrals of the downwash over the wing surface is extended as far as possible, and which has to be computed numerically;(ii) in which approximations are made for the upwash velocities in the neighbourhood of the leading edge, resulting in a series of standard integrals for the estimation of the pressure loading.Method (ii) is applied to the pressure loading on a flat plate triangular wing and cropped delta wing, and the application to more general shapes is discussed.
Approximation for the Effect of Twist on the Vibration of a Turbine Blade
Authors: Martin A. I. 
Published: July 2016

SummaryModern turbine blades are generally twisted about their axes, the shape resembling that of a helicoid. This makes the determination of their overtone frequencies much more difficult. The equations governing the flexural vibrations may be obtained from the Clebsch-Kirchhoff theory for rods which are naturally twisted. By using these equations, this paper considers a first-order approximation for the effect of uniform twist.
On the Stability of Accelerated Motion: Some Thoughts on Linear Differential Equations with Variable Coefficients
Authors: Collar A. R. 
Published: July 2016

Summary:In studies of the stability of aeronautical systems, equations of motion are derived which have coefficients dependent on flight speed. Conventional practice treats the speed as constant, when a set of linear differential equations with constant coefficients results. Actually, since the speed varies during flight, it may be regarded as a prescribed function of time; the set of linear differential equations then has variable coefficients.The treatment of the problem of stability then becomes much more complex in this case. A simple example is given to show that a system which is stable at any constant speed can become unstable during deceleration; the ordinary constant-speed criteria are, strictly, therefore inadequate. Some approaches to the discussion of stability during acceleration are suggested; a solution is given of the single second-order equation which enables the amplitude of oscillation of the solution to be studied. Inverse methods of approach are suggested, both for single and sets of equations, in which particular forms of acceleration corresponding to prescribed solutions are derived; and some tentative conclusions are drawn. As would be expected, the effects of acceleration depend on a dimensionless “acceleration number.”
A Random Distribution of Gusts Corresponding to a Measured Frequency of
Vertical Gusts
Authors: Fine M. 
Published: July 2016

Summary
The paper describes a method of estimating the frequency of gust
components in the plane of a propeller from measurements of
vertical gust components, which are those
generally recorded. By this means additional flight recording is avoided and
the danger of under-estimating the frequency of gusts affecting the
propeller is reduced. Random distribution of gusts in space is assumed. It
is found that gust components in the plane of the propeller of 10 ft./sec.
or more occur 2·51 times as frequently as vertical components of 10 ft./sec.
or more. For speeds greater than 10 ft./sec., the ratio is higher.
The Lift on a Thin Aerofoil with a Jet-Augmented Flap
Authors: Spence D. A. 
Published: July 2016

Summary
The method which was developed in an earlier paper for calculating the
lift on a thin jet-flapped aerofoil has been applied to the case in which
the jet enters the main stream tangentially from a deflected flap. The lift
derivative with respect to the (small) angle of deflection β is of the
form
where ,
E being the ratio of flap length to aerofoil
chord, and D0 a function
both of E and of the jet momentum coefficient
CJ. In the special
case CJ = 0,
Do vanishes and the
classical results for attached flow on flapped aerofoils without
super-circulation are obtained. More generally,
Do has been
evaluated over the range
0<CJ<5 for six
ratios E between 0·02 and 0·50, using an
electronic computer. The lift derivatives so found lie between those in the
limiting cases of “deflection” (E = 0) and “incidence” (E=1) which were
calculated in Reference 1. They show that the effectiveness of the jet-flap
scheme might be greatly increased by blowing over flaps of the order of 20
or 30 per cent of the chord, rather than over the small “shrouds” which have
hitherto been proposed.
The High Speed Flow of Gas Around Blunt Bodies
Authors: Serbin Hyman 
Published: July 2016

SummaryA number of results derived by the author in earlier reports on the flow of air around blunt bodies moving at high speed are here collected in a unified analysis. The theory predicts in a satisfactory way the shock shape and detachment distance for two blunt bodies, a flat disc and a sphere. It is shown that the density ratio across a normal shock is a useful parameter, combining the effects of both the free stream Mach number and the ratio of specific heats.