bluuebunny/crossref_metadata_2025_split huggingface dataset:
Vibration Characteristics of Straight Blades of Asymmetrical Aerofoil Cross-Section
Authors: Carnegie W. , Dawson B. 
Published: July 2016

SummaryTheoretical and experimental natural frequencies and modal shapes up to the fifth mode of vibration are given for a straight blade of asymmetrical aerofoil cross-section. The theoretical procedure consists essentially of transforming the differential equations of motion into a set of simultaneous first-order equations and solving them by a step-by-step finite difference procedure. The natural frequency values are compared with results obtained by an analytical solution and with standard solutions for certain special cases. Good agreement is shown to exist between the theoretical results for the various methods presented. The equations of motion are dependent upon the coordinates of the axis of the centre of flexure of the beam relative to the centroidal axis. The effect of variations of the centre of flexure coordinates upon the frequencies and modal shapes is shown for a limited range of coordinate values. Comparison is made between the theoretical natural frequencies and modal shapes and corresponding results obtained by experiment.
Transfer Matrices for Beams Loaded Axially and Laid on an Elastic Foundation
Authors: Djodjo B. A. 
Published: July 2016

SummaryUsing a modified model of the axially-loaded Timoshenko beam, nine field transfer matrices for the homogeneous case and three field matrices for the non-homogeneous case have been derived, covering thus all the “cases of state” of continuous beams loaded axially and laid on an elastic foundation. The loads and restraints (translatory and rotatory) may be both concentrated and distributed. The matrices make possible a simultaneous treatment of free vibrations, forced vibrations, statics and buckling.
Minimum Induced Drag of Non-Planar Ground Effect Wings with Small Tip Clearance
Authors: Kida T , Miyai Y 
Published: July 2016

SummaryThis paper treats theoretically the problem of the minimum induced drag of non-planar ground effect wings with both tips very close to the ground, within the limitations of the linearised lifting-line theory. The gap clearance between the wing tip and the ground is assumed to be very small and, using this small parameter, an approximate theory, which yields the minimum induced drag of a non-planar ground effect wing, is formulated by the method of matched asymptotic expansions. As a check on the accuracy of the method, this theory is compared with the exact theory for a semicircular wing. This shows that the present method is accurate within the small gap clearance. Moreover, the present method is applied to other wing configurations, such as semi-elliptic wings and wings with endplates, circular arc wings in a tube and circular arc wings. These computations show the theory to be very effective and it can be easily extended to various spanwise cambers.
A Stagnation Pressure Probe for Supersonic and Subsonic Flows
Authors: Goodyer M J 
Published: July 2016

SummaryThe usefulness of a probe which can sense the absolute value of the stagnation pressure in supersonic flow has long been recognised. In the past such a probe has not been available and therefore it has been necessary to infer this fundamentally important flow property from measurements of other properties. This paper describes a probe which has been developed specifically to measure accurately the stagnation pressure of a supersonic gas stream. Measurements of the performance of the probe to date show that it is capable of measuring absolute stagnation pressure with an accuracy of 0.1 per cent in the Mach number range 1.5 to 2.1. No measurements have yet been made in the transonic range, but at low subsonic speeds the probe has demonstrated its ability to measure dynamic pressure within an accuracy of 0.1 per cent at a Mach number of approximately 0.13. The permissible range of misalignment in pitch and yaw before the pressure recovery begins to deteriorate are functions of free-stream Mach number and are usefully wide.
Measurement of the Mean Pressure Distribution About a Double-wedge Strut in Turbulent Shear Flow
Authors: Turner J T , Turner M H , Williams K J 
Published: July 2016

SummarySurface pressure distributions have been measured on a cylinder with a double-wedge cross section in a two-dimensional channel flow. The flow is sheared in the direction of the cylinder axis, using a grid of parallel wires with variable spacing, in order to simulate the type of geometry and velocity variation which occur for annulus support struts in turbomachines. The strut had a 38° included angle at the leading and trailing edges and an aspect ratio of 1.33 based on the maximum thickness. This was fixed between the parallel walls of a rectangular wind tunnel with end leakage eliminated. Surface pressure distributions were measured over a Reynolds number range of 0.5 × 105 to 1.5 × 105 for three different shear flow conditions. Despite the presence of sharp edges at the mid-chord position, delayed boundary-layer separation beyond the plane of maximum thickness has been found for sufficiently high spanwise shear in the upstream flow. Surprisingly, therefore, some similarity with previous results for struts of circular cross section appears to exist. The influence of the shear flow conditions on the pressure drag force has been determined by numerical integration of the data. Only a slight dependence on the upstream flow conditions is found, although the effect of secondary velocity components may still be observed if the spanwise variations in the local drag force are examined.
Critical Buckling of Some Stiffened Panels in Compression, Shear and Bending
Authors: Plank R J , Williams F W 
Published: July 2016

SummaryPrevious papers by the authors and others have developed exact methods for computing the critical buckling loads of prismatic assemblies of rigidly interconnected thin flat rectangular plates. The plates may be isotropic or anisotropic and can carry uniform in-plane shear stresses and transverse stresses in addition to a longitudinal stress which varies linearly over the cross section but is longitudinally invariant. Published results obtained using these methods have only covered a few of the types of structure and loading which are of interest. This paper presents results which complement those already published. For instance, interaction curves are given for common types of panel in combined in-plane shear and longitudinal compression and bending. About half of these curves are nearly parabolic while some others differ greatly from the parabola, which errs on the safe side for all the results presented. Other results cover critical loads other than the lowest, panels with bulb flat stiffeners, as used for bridge decks, and the effects of assumptions usually made when idealising real panels before computation.
A Two-Dimensional Aerofoil with a Control Surface Oscillating at Low Frequency in High Subsonic Flow
Authors: Nixon D 
Published: July 2016

SummaryThe aerodynamic derivatives for a two-dimensional aerofoil with an oscillating control surface in a high subcritical flow are calculated using the method of Nixon. The aerofoil is assumed to be symmetric and at zero incidence with a zero mean control surface deflection angle. With the exception of the control surface stiffness derivative the magnitudes of the aerodynamic derivatives are greater than the corresponding linear values by between 15–35 per cent; the greatest difference occurs for low values of the frequency parameter. The magnitude of the control surface stiffness derivative is less than the corresponding linear value by the order 10–15 per cent.
The Prediction of Turbulent Boundary Layer Parameters in Conical Diffuser Flows
Authors: Wirasinghe N E A , Neve R S 
Published: July 2016

SummaryThe methods suggested by Ross and by Fraser for dealing with turbulent boundary layers in adverse pressure gradients using semi-empirical data are extended to the prediction of boundary layer growth in conical diffusers, the new method making no recourse to measured static pressures, as previously required. Predictions agree closely with published experimental data by Fraser and give some justification for the use of the Ross model for the turbulent boundary layer in a diffuser provided that the diffuser is not too long and that the inlet boundary layer is thin.
The Boundary Layer on a Plane of Symmetry
Authors: Head M R , Prahlad T S 
Published: July 2016

SummaryFor the turbulent boundary layer it is shown that, if an initial velocity profile is given, along with the local pressure gradient and shear-stress distribution through the layer, then the shape of the velocity profile a short distance downstream is unaffected by flow convergence or divergence, provided this is constant through the layer. For flow approaching an obstacle, increased divergence close to the surface is shown to account for the marked changes in profile shape that have been observed.
Simple Formulae for Supersonic Flow past a Cone
Authors: Hui W H 
Published: July 2016

SummaryThe problem of the supersonic flow with attached shock wave past a circular cone at zero angles of attack is treated, using the thin-shock-layer expansion. The solution is calculated to the fourth approximation. A simple formula is then derived for the surface pressure coefficient by the application of the parameter-straining technique and it is shown to be very accurate for the whole Mach number range for which the shock remains attached to the cone vertex.
Orbital and Attitude Stability of Space Shuttles in Parking Orbits
Authors: Arho R 
Published: July 2016

SummaryA unified treatment is given of the orbital and attitude stability of space shuttles in parking orbits (in vacuo) in the earth’s gravitational field. A shuttle in a circular orbit with a principal axis aligned with the horizontal in the orbital plane is found to be in stationary geostatic equilibrium. The demand for stability leads to a condition which must be satisfied by the principal moments of inertia. The stability which is achieved is not asymptotic without control. The stationary state is a stable centre about which a bounded perturbation oscillation without damping may exist.
The Application of a Lifting-Surface Method to Large, Steady or Oscillating Models in Subsonic, Closed, Open or Slotted Wind Tunnels
Authors: Streather R A 
Published: July 2016

SummaryA subsonic, lifting-surface method is extended to apply to low-frequency oscillations of wind-tunnel models, taking into account both longitudinal and lateral variations of tunnel lift interference. Rectangular sectioned tunnels with closed, slotted or open roof and floor and closed sidewalls are considered. A comparison is made between the aerodynamic derivatives obtained by this method and those calculated with the assumption that the model span is small compared to the tunnel width. Three models of aspect ratio 2.67 and different sweepback are considered in rigid pitching oscillations in tunnels of width/height ratio 2.5. The greatest differences between the results from the two methods occur for the tunnel with closed roof and floor and for the unswept planform. The least differences occur for the slotted tunnel and for the planform of greatest sweepback. The results indicate that, for models of conventional size [up to span/(tunnel width) ratio of 0.4], the “small-span” assumption is satisfactory in tunnels with slotted roof and floor and closed side walls, but not in fully closed tunnels.
An Extension of One-Dimensional Theory to Inviscid Swirling Flow through Choked Nozzles
Authors: Carpenter P W , Johannesen N H 
Published: July 2016

SummaryA method is presented for determining the swirling compressible flow through a nozzle, given conditions at a reference section. The principal assumption is that changes in the nozzle cross-sectional area are sufficiently gradual for the radial velocity component to be neglected at each section, i e, the usual assumption of one-dimensional compressible flow theory. This method is used to determine choked-flow conditions in the case where there is solid-body rotation at the throat for a range of swirl intensities with the ratio of the specific heats taking various values. Mass-flux coefficients and impulse functions are determined. Sonic surfaces, velocity profiles and other characteristics of interest are also presented. An approximate analysis valid for low swirl intensities is developed and analytical formulae are derived for most quantities of interest. The main conclusion of practical importance is that the introduction of swirl to compressible nozzle flows need not lead to a significant reduction in specific thrust. Further exploration of the possible effects of swirl on noise during the relatively short take-off and landing periods cannot therefore be ruled out on the grounds that swirl would lead to excessive thrust losses.
Analysis of High-Lift Wing Systems
Authors: Goradia Suresh H , Colwell Gene T 
Published: July 2016

SummaryA method which can be used for the design of blown or unblown wing sections is described in this paper. A brief description of a variety of theoretical methods for computation of different fluid flow phenomena encountered on high-lift wing systems is presented. The most significant type of viscous flow - a confluent boundary layer flow, which is present on the upper surface of the flap, the vane and the main component of a high-lift system – is described and its importance to the performance of high-lift systems is illustrated. Results of computation of pressure distribution, boundary-layer characteristic, and lift coefficient for two-dimensional high-lift systems are compared with experimental data in order to establish the validity and limitations of the method.
Eddy Viscosity and Mixing Length from Measured Boundary Layer Developments
Authors: Galbraith R A McD , Head M R 
Published: July 2016

SummaryTo obtain profiles of shear stress and eddy viscosity, the boundary-layer equations in finite-difference form have been applied to published turbulent-boundary-layer developments measured in nominally two-dimensional conditions. In applying this procedure, measured velocity profiles have been represented by members of Thompson’s profile family. Except close to separation, these representations are very satisfactory, and derived shear-stress profiles are generally in good agreement with direct measurements. Various eddy-viscosity and mixing-length models are compared with the results of the analysis and are found in general to differ widely among themselves and from the present results. The widely used assumption,l= ky in the wall region, appears to be invalid.
The Flow Over a “High” Aspect Ratio Gothic Wing at Supersonic Speeds
Authors: Narayan K Yegna 
Published: July 2016

SummaryResults are presented of an experimental investigation on a non-conical wing which supports an attached shock wave over a region of the leading edge near the vertex and a detached shock elsewhere. The shock detachment point is determined from planform schlieren photographs of the flow field and discrepancies are shown to exist between this and the one calculated by applying the oblique shock equations normal to the leading edge. On a physical basis, it is argued that shock detachment has to obey the two-dimensional law normal to the leading edges. From this, and from other measurements on conical wings, it is thought that the planform schlieren technique may not be particularly satisfactory for detecting shock detachment. Surface pressure distributions are presented and are explained in terms of the flow over related delta wings which are identified as a vertex delta wing and a local delta wing. The forces acting on the wing are calculated and are shown to be very close to the two-dimensional wedge values over a wide range of incidence. In particular, it is shown that this wing, compared to one which supports a fully detached shock wave, generates a higher lift/(pressure drag) ratio at a given lift coefficient.
Numerical Computations of the Flow in Curved Ducts
Authors: Pratap V S , Spalding D B 
Published: July 2016

SummaryThe paper describes the application of a recently developed numerical scheme to the computation of the flow in a curved duct. The flow situation is partially-parabolic in nature as there are significant elliptic effects, which are transmitted through the pressure field. The turbulence model used comprises two differential equations, one for the kinetic energy of turbulence and the other for its dissipation rate. It has been observed that the predictions using the new procedure agree very satisfactorily with the experimental data. Comparisons are also made with the predictions of a fully-parabolic calculation procedure.
Blockage Effects on Two-dimensional Bluff Body Flow
Authors: Fackrell J E 
Published: July 2016

SummaryThe time mean flow past a two-dimensional bluff body in a wind-tunnel is modelled by an adaptation of the numerical free-streamline method of Bearman and Fackrell. Provided the base pressure and separation positions are specified in advance, the method allows the calculation of the flow field outside the wake and in particular of the pressures on the wetted surface of the body. Good agreement of the predicted pressures with experimental results is obtained for a flat plate, wedge and circular cylinder at various blockage ratios. In addition to predicting the confined flow, it is shown that a free-air base pressure can be simply deduced from the confined base pressure. With an assumption that the separation positions are unaffected by blockage, this allows the free-air flow field to be calculated. By using an analogy to Roshko’s Strouhal number, which has been found to be invariant under constraint, a free-air Strouhal number can also be deduced.
A Correlation between Pressure and Heat Transfer Distributions at Supersonic and Hypersonic Speeds
Authors: Stollery J L , Coleman G T 
Published: July 2016

SummaryThe “reference enthalpy” and local flat plate concepts are used to derive some simple expressions for the turbulent heat transfer rate distribution over an arbitrary body at supersonic and hypersonic speeds. The connection between pressure and heat transfer rate is established and tested against a number of experimental data.
A Reference-Plane Method for the Solution of Three-Dimensional Supersonic Flows
Authors: Camarero R 
Published: July 2016

SummaryA numerical method for the solution of three-dimensional supersonic flows and the associated computer programme have been devised. The present algorithm is based on a reference-plane characteristic network. The physical region between the shock wave and the body surface is replaced by a computational mesh facilitating the incorporation of different boundary conditions and arbitrary body shapes. For reasons of stability and computing time a Hartree-type grid was used where the characteristic segments are projected upstream. The base points do not coincide with nodal points and interpolation by means of Tchebycheff polynomials is required to obtain the flow properties. Numerical differentiation is carried out by means of spline functions. The programme has been used and verified under a wide variety of flows past circular and elliptic cones, tangent ogives and a delta wing body. After a series of numerical experiments it was found that accurate solutions could be found using a 7 × 7 grid, and that the essence of the solution is preserved using a very coarse mesh of 4 × 4. Furthermore, the good agreement obtained with experimental results indicates that it could be applied successfully to problems of practical interest.
A General One-Dimensional Theory of Compressible Inviscid Swirling Flows in Nozzles
Authors: Carpenter P W 
Published: July 2016

SummaryAn approximate analytical method is presented for determining the swirling compressible flow through a nozzle. The method is developed from the techniques introduced by Carpenter and Johannesen. It is perfectly general in that the swirl distribution need not be specified a priori but the radial gradients of the stagnation enthalpy and entropy are assumed to be small. The principal assumption is that changes in the nozzle cross-sectional area are sufficiently gradual and smooth for the radial velocity component to be neglected at each section, i e the usual assumption of one-dimensional compressible flow theory. Analytical expressions are derived for various flow characteristics, e g mass-flux coefficient, impulse function and back-pressure ratio required for choking. The analytical results are compared to numerical results for two main classes of swirling flows. On the whole the analytical results are found to be good approximations for moderate swirl levels. The approximate numerical method is found to be reasonably successful at predicting flow reversal at the nozzle wall. The main result is that a swirl parameter is found such that, with the sole exception of the free-vortex case, the mass-flux-coefficient data for all swirling flows investigated collapse onto a single curve.
An Optical Instrument for Measuring Fluctuating Velocities in Highly Turbulent Flows
Authors: Gaster M. , Maybrey J.F.M. 
Published: July 2016

SummaryFlow measurement by optical devices of various types, particularly those involving laser light sources, have received considerable attention over the last few years. Different schemes employing a wide range of optical layouts have evolved and the resulting signals have been processed in a number of ingenious ways. We report new experimental work on an optical instrument that can be considered as the forerunner of the laser anemometer in the belief that in certain circumstances this particular optical layout offers some real advantages over the majority of laser anemometers. One important advantage of this system is the ease with which both the shape and size of the sampling zone can be independently controlled. Another is the ability to position the sampling region very close to a boundary without having to contend with the surface reflection difficulties that often prevent such measurements being made with laser optics. The instrument measures the velocities of small particles suspended in the fluid in much the same way as the laser anemometer. In unsteady flows this results in a series of velocity estimates generated at random time instants. These intermittent samples of the velocity are used to form power spectral density estimates by methods recently developed for the analysis of randomly sampled records (Gaster and Roberts, 1975 & 1976). This method of analysis could well be applied to the processing of the signals generated by laser anemometers operating in the burst counter mode.
Changes in Conical Diffuser Performance by Swirl Addition
Authors: Neve R.S. , Wirasinghe N.E.A. 
Published: July 2016

SummaryIt has been found that the addition of a whirl velocity component to an otherwise axial flow in a conical diffuser can lead to improvements in static pressure recovery and in efficiency, according to a restricted definition. Diffusers of total conical angle 10, 20 and 30 deg. were tested in detail; improvements were evident only in the last two, which would otherwise have suffered from flow separation problems caused by their relatively large divergence angles. The agency for improvement seems to be a beneficial redistribution of axial velocities.