bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Influence of Aspect Ratio on Incompressible, Turbulent Flows From Rectangular Slots
Authors: Marsters G.F. , Fotheringham J. 
Published: July 2016

SummaryJets issuing from rectangular slots cut in thin plates exhibit some unusual features, including unequal spreading rates in the spanwise and transverse directions, the appearance of velocity peaks near the “ends” of the jet and changing rates of centreline velocity decay in the downstream direction. This study examines the effects of aspect ratio on such flows. The flow field has been investigated using both total head tubes and hot wire anemometry. The results are presented in the form of three-dimensional plots of total pressure and contour maps of constant velocity, streamwise turbulence intensity and the Reynolds shear stresses. The decay of mean velocity and stream-wise turbulence intensity along the centreline are presented. The rates of spanwise spreading and the location of the velocity peaks at various downstream stations are discussed. If the aspect ratio is small enough, spanwise peaks in the mean velocity distribution are suppressed.
Measurements of Dynamic Stability Derivatives of Hyperballistic and Conic Shapes at M = 6.85
Authors: Qasrawi A.M.S. , East R.A. 
Published: July 2016

SummaryExperimental measurement of the pitching stability derivatives and of AGARD hyperballistic standard models HB1 and HB2, a hemisphere-cylinder double flared configuration designated HBS and three 10° semi angle cones of bluntness ratios 0.0, 0.2 and 0.4 are reported. Data were obtained at a Mach number of 6.85 in a short duration light piston tunnel using the small amplitude free oscillation technique. The tests were conducted at Reynolds numbers from 0.2 × 106 to 0.85 × 106, based on centre-body diameter, for the hyperballistic shapes and from 1.45 × 1016 to 2.17 × 106, based on base diameter, for the conical shapes. The mean angle of attack was varied from 0 to 17.0 degrees and the frequency parameter from 0.0020 to 0.0043 for the hyperballistic shapes and from 0.0018 to 0.0092 for the cones. All models tested were found to be dynamically stable for all positions of the axis of oscillation considered. The significant observed non linear variations of the damping derivative with angle of attack for the 0.2 and 0.4 bluntness cones and the HB2 shape could be partially accounted for qualitatively by boundary layer transition induced effects. The variation of the derivatives with angle of attack for the pointed cone were consistent with a fully turbulent boundary layer, whereas it was probable that for the HB1 and HBS models the boundary layer remained laminar throughout. Variation of the frequency parameter resulted in no significant effect on the measured stability derivatives.
On the Decay of Laminar Jets in Ambient Streams
Authors: Middleton D. 
Published: July 2016

SummaryEarlier analysis, Middleton, of the laminar discharge of a ‘strong’ incompressible jet, due to a line or point source of momentum, into an unbounded co-flowing stream of the same density, is extended to the case of plane and round ‘weak’ jets the velocity in which only slightly exceeds the ambient velocity. In addition to recovering Goldstein’s solutions for ‘wake-like’ flows, use of the momentum integral equation provides approximate relationships for the decay of the centre velocities from the strong to the weak situations. Comparison is made with Wygnanski’s perturbation approach, suitably extended, and it is concluded that for the plane jet case, for which the agreement is better, the curve for the centre-plane velocity is correct to within about 12% throughout its range. The present approach is applicable to any flow for which a similarity solution exists as a first order solution, and is especially suitable when two such solutions exist for large and small values of an appropriate parameter. Its use also throws light on the form to be adopted for a perturbation expansion.
Part I: Chordwise Distribution of Fluctuating Pressure
Authors: Wilkinson R.H. 
Published: July 2016

SummaryThe fluctuating loading on a cylindrical bluff body due to vortex shedding increases if the body is capable of vibration. This is a result of amplification of the fluctuating pressures around a two-dimensional section of the body together with an improvement of the spanwise correlation of the vortex shedding. Measurement of the fluctuating forces on the cylinder during this process gives no guide as to the relative magnitude of these effects. In this paper, root mean square fluctuating pressure distributions and pressure correlations across a chord are presented for a square cylinder with front face normal to the approach flow whilst stationary and during forced vibration. The fluctuating lift coefficient for a two-dimensional section of the cylinder and its maximum amplification during vibration are calculated.
Evaluation of Two-Dimensional Subsonic Oscillatory Airforce Coefficients and Loading Distributions
Authors: Salmond Deborah J. 
Published: July 2016

SummaryA method is described for calculating numerically the aerodynamic stiffness and damping coefficients and loading distributions for a two-dimensional thin aerofoil oscillating harmonically in subsonic flow, from the Possio Integral Equation by approximating the loading by a finite series of basis functions. Sample loading distributions obtained by using the method are presented for a Mach number of 0.9 and a frequency parameter of 0.4.
Two-Dimensional Flow at Right Angles to a Flexible Membrane
Authors: Newman B.G. , Low H.T. 
Published: July 2016

SummaryIncompressible flow perpendicular to a flexible, impervious membrane has been studied for two-dimensional conditions. The membrane was mounted on relatively thin supports spaced c apart. Measurements of drag, base pressure and the frequency of membrane oscillation are presented for various lengths ℓ, and for two densities, of membrane. These parameters are related to one another theoretically and in particular Bearman′s universal correlation for Strouhal number agrees with the experimental results. It is found that for values of< 0.50 the drag is independent of membrane density. The drag decreases at larger values ofand this is related to a periodic reattachment of the separated flow to the back of the membrane. For a given ℓ the drag is greatest whenis very small and the membrane is almost flat.
Streamwise Corners with Curvature Independent of Streamwise Distance
Authors: Barclay W.H. , Ridha A.H. 
Published: July 2016

SummaryA two parameter approximate solution is presented for the flow along a streamwise corner having large, possibly infinite, curvature in its region of transition between the two quarter infinite planes which form its asymptotes. The two parameters are the angle between the asymptotes and a quantity proportional to the ratio of the local two-dimensional boundary layer thickness and the radius of curvature of the corner at the symmetry plane. Relative to the corner of infinite curvature (sharp corner) a finite curvature always tends to modify the solution towards that for a flat plate. This implies that for corner angles less than 180° the corner layer thickness in the symmetry plane is less than that for the sharp corner of the same angle and the shear stress is higher, the converse holding for angles greater than 180°. The flow in planes normal to the free stream direction is rather complex and typically there is a reversal in its direction within the symmetry plane.
The Effect of Disturbed Turbulence Structure on the Preston-Tube Method of Measuring Wall Shear Stress
Authors: Kiske S. , Ram V. Vasanta , Pfarr K. 
Published: July 2016

SummaryThe subject of this paper is the effect of a disturbance to the turbulence structure of the flow on the reading of a Preston tube used to measure wall shear stress. Two kinds of disturbance have been studied experimentally, one caused by reattachment and the other by an abrupt change in wall roughness. The apparent wall shear stress measured by the Preston tube both in channel and boundary layer flows with these kinds of disturbance has been compared with the wall shear stress measured by a sublayer fence. The results give an idea of the magnitude of the error that is likely to arise when the Preston tube is used in a flow with disturbed turbulence structure.
Characteristics of Poiseuille Flow in a Divided Channel
Authors: Zamir M. , Camiletti S.E. 
Published: July 2016

SummaryThe problem considered is that of Poiseuille flow in a two dimensional channel impinging on a flat plate placed symmetrically between the two channel walls so as to bifurcate the channel into two equal branches. The results of a theoretical study of the problem are presented and analysed to portray in full details the characteristics of the flow before and after the bifurcation point. In particular the effects of the flow divider on the flow near the channel walls and the effects of the channel walls on the flow near the flow divider are examined.
Pitch/Yaw Coupling Due to Roll of an Axisymmetric Missile with Autopilot
Authors: Fortescue P.W. 
Published: July 2016

SummaryThe types of pitch/yaw coupling which may result from roll motion of a conventional tail-controlled cartesian missile have been categorised. The consequences of the couplings upon:(a)the response to a step demand for manoeuvre, and(b)the decay of error in a beam-rider system are presented.Potentially the most damaging forms of coupling are due to(a)mis-match of the Invariant Frames of airframe and servos,(b)angular mismatch between parts of the system, and(c)gyroscopic coupling.
Asymmetric Vortex Formation from Cones at Incidence – a Simple Inviscid Model
Authors: Dyer D.E. , Fiddes S.P. , Smith J.H.B. 
Published: July 2016

SummaryAn inviscid model, originally proposed by Bryson to describe the formation of laterally-symmetric vortices above bodies of revolution at large angles of incidence, is extended to describe flows without lateral symmetry. Each vortex is represented by a single line-vortex and conditions of cross-flow stagnation are applied at the postulated separation lines. The transverse component of the force acting on each vortex is balanced by an equal and opposite force acting on the cut connecting it to the adjacent separation line. It is shown that this model allows asymmetrical vortices to form in the flow over slender circular cones even when the separation lines are disposed symmetrically.
Swirl Characteristics of an S-Shaped Air Intake with both Horizontal and Vertical Offsets
Authors: Guo R.W. , Seddon J. 
Published: July 2016

SummaryAs part of a series of investigations of the swirl in S-ducts, the present paper gives the results of tests on a duct with both horizontal and vertical offsets, for comparison with earlier work on ducts with horizontal offset only. Results obtained bear a similarity to those of Reference 2, for which the duct had the same cross-sectional shapes and areas, but the addition of a vertical offset magnifies the resultant swirl considerably. As before, the swirl is found to be sensitive to entry conditions, in that a solid spoiler, blocking off 15% of entry width from the inside wall, reverses the sense of the final swirl. Taken overall, the results throw additional light on the nature of the swirl problem. A particularly interesting and potentially important correlation is obtained between the final swirl (in magnitude and sense of rotation) and a pressure difference between the top and bottom walls of the duct, taken in the end plane of the second bend.
On the Energy Characteristics of the Aerodynamic Matrix and the Relationship to Possible Flutter
Authors: Jones J.G. 
Published: July 2016

SummaryThe problem of energy transfer between an airstream and a wing in sinusoidal motion has been investigated by a series of authors beginning with Frazer who in 1939 considered the power input required to maintain forced oscillations of an aeroplane wing in flight. More recently Nissim introduced an ‘aerodynamic energy concept’ as the basis for the design of active control systems for flutter suppression. In this paper the author reconsiders the energy characteristics of the aerodynamic matrix in terms of the network concepts of resistive and reactive elements, corresponding to energy dissipation and energy storage respectively. A dual formulation of Nissim’s method is described and an extension proposed that takes account of aerodynamic energy storage in addition to aerodynamic energy dissipation.
Added Fluid Mass and the Equations of Motion of a Parachute
Authors: Eaton John A. 
Published: July 2016

SummaryWhile it has long been known that added fluid mass may be important in the dynamics of parachutes, due to inadequate or incorrect derivation and/or implementation of the added mass tensor its full significance in the stability of parachutes has yet to be appreciated. The concept of added mass is outlined and some general conditions for its significance are presented. Its implementation in the parachute equations of motion is reviewed, and the equations used in previous treatments are shown to be erroneous. A general method for finding the equivalent external forces and moments due to added mass is given, and the correct, anisotropic forms of the added mass tensor are derived for the six degree-of-freedom motion in an ideal fluid of rigid body shapes with planar-, twofold- and axisymmetry, These derivations may also be useful in dynamic stability studies of other low relative density bodies such as airships, balloons, submarines and torpedoes. Full nonlinear solutions of the equations of motion for the axisymmetric parachute have been obtained, and results indicate that added mass effects are more significant than previously predicted. In particular, the component of added mass along the axis of symmetry has a strong influence on stability. Better data on unsteady forces and moments on parachutes are needed.
Approximate Displacements of Exact Membrane Actions in a Shell Triangular Element
Authors: Morley L.S.D. 
Published: July 2016

SummaryExact stress functions which satisfy the homogeneous differential equations of equilibrium for membrane actions are available from the static geometric analogue of previously derived exact displacements of inextensional bending. For finite element evaluation it is necessary to know the displacements (and rotations) caused by these membrane actions. A method of calculating approximate displacements is described which uses the principle of minimum potential energy. Results are given for specimen triangular elements with positive, zero and negative Gaussian curvatures. A listing is appended of a Fortran computer program which allows calculation of these approximate displacements, rotations and other physical quantities for other element shapes.
A Model for Studying the Stress-Field around Simple Fractures in Human Patella
Authors: Misra J.C. , Murti V.V.T.N. 
Published: July 2016

SummaryA mathematical model for estimating the stress-field in the vicinity of cracks in human patella has been studied. In conformity with experimental observations with regard to the mechanical properties of osseous tissues, elasticity and anisotropy of the patella have been paid due consideration. The present study being analytical, the problem is first formulated mathematically, and posed as a boundary value problem. Using Mellin transforms technique, the problem is reduced to solving a Fredholm integral equation which is treated numerically by employing Chebyshev quadrature formula. Numerical results are presented. It is suggested that the techniques used may also find application to engineering structures.
The Distribution of Pressure on an Aerofoil, in a Stream with a Spanwise Velocity Gradient
Authors: Mair W. A. 
Published: July 2016

SummaryPressure measurements were made at one section of an aerofoil of constant chord spanning a wind tunnel. A flat plate was mounted in the tunnel upstream of the aerofoil, so that the wake from the plate produced a spanwise velocity gradient at the aerofoil. By traversing the plate across the tunnel the position of the wake could be altered relative to the pressure holes in the aerofoil, so that the complete pressure distribution over the aerofoil in the neighbourhood of the wake could be found. The results showed that, because of the secondary flow produced by the interaction between the aerofoil and the wake, the variation of pressure across the wake for a given chordwise position was very small, except close to the leading edge. Thus the lift coefficient, based on the velocity outside the wake, was nearly constant across the wake. The form drag coefficient, based on the same velocity, was considerably reduced in the wake. Even when the form drag coefficient was based on the local velocity of the stream, a considerable reduction was found in the wake.
Experiments with an Electrical Analogue for the Extension and Flexure of Flat Plates
Authors: Palmer P. J. , Redshaw S. C. 
Published: July 2016

SummaryDetails of the design, construction and use of an electrical resistance network for solving certain of the problems encountered in the flexure and extension of flat plates are given. Some typical experiments have been carried out with the aid of this network and the method of operation of the analogy is described. The results of these experiments are presented and they are compared with the corresponding theoretical values. The comparison is as good as could be expected in view of the limitations imposed by the very coarse mesh which was used; essentially the same results would have been obtained by the exercise of a relaxation computation, using the same size of net. No practical difficulties would be encountered in building a large network having a very fine mesh.
The Drag of Non-Planar Thickness Distributions in Supersonic Flow
Authors: Graham E. W. , Beane B. J. , Licher R. M. 
Published: July 2016

SummaryFor many conventional aircraft, the thickness of the wing and fuselage can be represented approximately by source distributions in the plane of the wing and on the axis of the fuselage. Such aircraft may be considered as having essentially planar thickness distributions. However, missiles with cruciform wings, biplane arrangements, “ ring ” wings and so on, require non-planar source distributions to represent the wing and fuselage thickness. For this reason, the term “ spatial thickness distribution ” is used.To simplify the investigation of spatial thickness distributions, a singularity representing an element of volume is introduced. It is shown that the optimum distribution of such elements in a prescribed space gives rise to a minimum wave drag value consistent with that obtained for a Sears- Haack optimum body of revolution.
The Buckling and Bending of Orthotopic Sandwich Panels With All Edges Simply-Supported
Authors: Robinson J. R. 
Published: July 2016

SummaryA formula is derived for the buckling in compression of an orthotropic sandwich panel, with all edges simply-supported. Two special types of symmetrical sandwiches, that of a sandwich having zero core flexural stiffnesses and of a corrugated core sandwich, are considered, and curves giving the critical buckling end load per inch are presented. An approximate theory is also given for the bending of sandwich panels under the action of an axial compressive load and a uniform lateral pressure. Curves are presented giving the maximum bending moments in a corrugated core sandwich panel.
Dynamic Problems of Interplanetary Flight
Authors: Lawden Derek F. 
Published: July 2016

SummaryThe solution to the general problem of transferring a rocket between two terminals in space with minimum fuel expenditure is explained and the results obtained when application is made to a number of particular problems of space navigation are described. The mathematical techniques which may usefully be employed in the calculation of optimum rocket trajectories are exemplified by a method of solving the problem of obtaining maximum range from a rocket missile over the Earth's surface.
Compressible Subsonic Flow in Two-dimensional Channels
Authors: Woods L. C. 
Published: July 2016

SummaryEquations for the calculation of the subsonic flow of an inviscid fluid through given two-dimensional channels (the “ direct” problem), and for the design (the “ indirect” problem) of such channels are derived. The method is based on conformal mapping, and in the special case of channels with walls made from a number of straight sections, or with wall pressure prescribed as step-functions, yields the same results as the well-known Schwarz-Christoffel mapping theorem technique. However, it is more general than this latter method, since it is capable of dealing with curved walls or continuously varying wall pressures. The compressibility of the fluid is allowed for only approximately, the ideal gas being replaced by a Kàrmàn-Tsien tangent gas.In Part II the theory is applied to various problems of aeronautical interest, perhaps the most important of which is to the setting of “ streamlined ” walls about a symmetrical aerofoil placed in the centre of the channel.
Photoelastic Investigation in Connection with the Fatigue Strength of Bolted Joints
Authors: Jessop H. T. , Snell C. , Holister G. S. 
Published: July 2016

SummaryThe elastic stress distribution around a circular hole in a flat bar under simple tension, when the hole is filled by a push-fit pin, was investigated photoelastically. Over a range of values of the ratio of hole diameter to width of bar, and for pins of differing Young's moduli, the effect of the pin was sensibly the same, namely, to reduce the maximum tension on the hole boundary by about 15 per cent, as compared with that in the unfilled hole.The maximum shear stress on the boundary was unaltered.
Compressible Subsonic Flow in Two-dimensional Channels
Authors: Woods L. C. 
Published: July 2016

SummaryThe theory developed in Part I is applied to a number of problems of aeronautical interest, the most important of which is to the setting of “ streamline “ walls about a symmetrical aerofoil placed in the centre of a channel. It is shown how the position of the streamline wall can be deduced from the (experimentally determined) position of a constant pressure wall. This theory is applicable to symmetrical aerofoils of any given shape, and makes allowance for the presence of the aerofoil's wake. To illustrate the theory, and to test it by an extreme example, the flow is calculated about a circular cylinder, with a diameter about half the tunnel height, for both straight and constant pressure walls. The solid blockage is calculated in each case and compared with the standard first order theory. For this extreme example the standard theory fails badly for straight walls, but is reasonably accurate for constant pressure walls.