bluuebunny/crossref_metadata_2025_split huggingface dataset:
Measurements in an Axisymmetric Turbulent Boundary Layer Along a Circular Cylinder
Authors: Afzal Noor , Singh K P 
Published: July 2016

SummaryIn an axisymmetric turbulent boundary layer along a circular cylinder at constant pressure, measurements have been made of mean velocity profile and turbulence characteristics: longitudinal velocity fluctuations, Reynolds shear stress, transverse correlation and spectrum. It has been found that the qualitative behaviour of an axisymmetric turbulent boundary layer is similar to that of a two-dimensional boundary layer in the wall region, where as in the outer region the effects of transverse curvature are observed.
Aerodynamic Throttling of a Two-Dimensional Flow by a Thick Jet
Authors: Stek J B , Brandt H 
Published: July 2016

SummaryThe velocity and pressure distributions in a flow generated by a thick air jet that throttles a confined airstream have been studied analytically and experimentally. Velocity and pressure measurements were made in a duct with a rectangular cross section of 102 mm height and 19 mm depth, through which air flowed at velocities ranging from 65 to 80 m/s. The airstream was throttled by a thick air jet having velocities ranging from 130 to 150 m/s that entered the mainstream at angles ranging from 60° to 135°. The jet-mainstream contour was found to be elliptical and agreement within six per cent was obtained between the theoretically and experimentally determined maximum height of the contour. Jet spreading was found to be linear. The theory permits determination of the velocity profile in the jet and gives velocities that deviate less than ten per cent from values obtained experimentally.
An Experimental Study of the Static and Dynamic Behaviour of a Tensioned Sheet with a Rectangular Opening
Authors: Datta P K 
Published: July 2016

SummaryThe results of an experimental study of the buckling and vibration behaviour of tensioned sheets with a rectangular opening are presented. The buckling phenomenon involves the existence of a non-uniform pre-buckle stress state in the vicinity of the opening. The local buckling load has been estimated on the basis of the modified Southwell method. The effect of parameters like cut-out size, sheet width, sheet thickness and cut-out corner radius has been investigated. The data from the vibration experiments indicate that the load versus frequency behaviour is dependent on the size of the test specimen and the opening shape. It has been observed that, for certain combinations of plate and opening parameters, the load versus frequency plot has a minimum corresponding to the local buckling of the free edge of the hole. For other plate and opening parameters it shows only a kink corresponding to the local buckling of the free edge of the cut-out. The buckling load for the opening shapes obtained from both the static and dynamic experiments are compared, showing good agreement.
Two-Dimensional Aft Bodies for Minimum Pressure Drag in Supersonic Flow
Authors: Viswanath P R , Narasimha R 
Published: July 2016

SummaryThe base pressure correlation proposed earlier by the authors, to take into account the effects of the boundary layer and of the boat-tail angle, is utilised in the design of two-dimensional aft bodies for minimum drag in supersonic flow. The general advantages of boat-tailing are indicated and charts of optimum profile parameters and minimum drag are provided for use in preliminary design. The effects on aft-body drag of possible reversion of the boundary layer at a sudden expansion are discussed, and the relevance of the optimum shapes found to the lifting case is indicated. The calculated optimum geometry is in good agreement with the experimental results of Fuller and Reid.
An Alternative Analytical Method for Ground-Effect Aerofoils
Authors: Kida T , Miyai Y 
Published: July 2016

SummaryAn alternative analytical method is applied to interference problems of an aerofoil very close to the ground, such as a free surface, a solid wall, and a slipstream. The method of matched asymptotic expansions on the small ground clearance is used in the governing integral equation and this analysis is different from Widnall and Barrows’s analysis. They used the matched asymptotic method in the differential equation. To show that the present method is reasonable, the problem of a ground-effect aerofoil in uniform fluid flow is considered and it is found possible to obtain the same results as those of Widnall and Barrows for the case of small ground clearance. By comparing with some earlier studies, it is found that the asymptotic method used with small ground clearance is valid for a clearance less than about 0.3 of the chord length. Next, the interference of ground-effect aerofoils in the channel wall, in a free jet stream, and in a slipstream are examined, and it is found that the present method can be easily applied to these problems.
The Aerodynamic Efficiency of Windmills
Authors: Lilley G M 
Published: July 2016

SummaryThe paper reproduces the results of an earlier report on the vortex theory of windmills and follows that theory through to establish the aerodynamic design procedure for a horizontal axis windmill. The results are shown to differ considerably from those given in a recent paper by Griffith and the differences are explained. The main conclusion is that, when full allowance is made for the drag of the blades, hub and tip losses, and losses due to interference with the support tower, the power output coefficient or efficiency of a horizontal axis windmill cannot exceed 30 to 35 per cent, as compared to an ideal efficiency of 59 per cent.
On the Calculation of the Incompressible Flow Past an Aerofoil with a Jet Flap
Authors: O’Mahoney R. , Smith F.T. 
Published: July 2016

SummaryThe incompressible planar flow past a wing with a jet issuing from the trailing edge is calculated by two separate methods, both adaptations of conformal mapping routines that are numerically exact in the jet-free case. These are the well-known circle mapping method and the halfplane method. The former is rendered inexact by the jump conditions across the jet and an approximation is necessary. The halfplane method, however, remains exact in principle, and a range of results is presented below. The most accurate of the previous calculations is verified, and comparisons between the halfplane and circle methods are also made. The halfplane scheme seems well suited for such wake-controlled flows and has been extended to transonic conditions in a related study.
Experiments on the Laminar Flow in a Rectangular Streamwise Corner
Authors: El-Gamal H.A. , Barclay W.H. 
Published: July 2016

SummaryThe results of measurements in the flow along a rectangular corner are presented in the form of velocity profiles. The profiles form two sets: one for flow in a slightly favourable streamwise pressure gradient and one for flow when the pressure gradient is ‘practically zero’. The appearance of the profiles is quite different from that of previously reported experimental work and it is suggested here that the primary cause of this is the different type of corner leading edges used in each case. The flow appears to be only marginally stable and even very slightly changed entry conditions caused by alterations in the leading edge geometry may have a marked effect on the profiles further downstream. The new results are consistent with the notion of corner layer similarity (an implication in every attempted theoretical solution) but there remains a significant difference between the experimental results and the more reliable theoretical solutions available.
Two Different Theoretical Approaches to the Base Pressure Problem in Two-Dimensional Supersonic Flow
Authors: Tanner M. 
Published: July 2016

SummaryThe basic physical idea underlying the theories based on the flow model of CHAPMAN and KORST is that the base pressure can be predicted if the pressure at the reattachment point is known. In the new theory of TANNER the fundamental idea is the connection between the drag of the body and the entropy increase in the flow. This paper presents the essence of both theories together with theoretical and experimental results.
The Aerodynamic Performance of a Freely Hinged Door between Two Flows
Authors: Hunt B.L. , Bizon S.A. , Taylor S.A. , Wilson D.A. 
Published: July 2016

SummaryThis paper reports experimental results for the performance of a freely hinged door between two incompressible air flows of different total pressures and different velocities. The apparatus used is a laboratory idealisation of the tertiary door system for an aircraft propulsion nozzle. The governing parameters are identified and the performance is presented in terms of the equilibrium door angle and the relative magnitude of the mass flow admitted. Three doors of different shapes were used and results are also presented for a plain opening. The main aerodynamic parameters are shown to be the velocity ratio and a non-dimensional pressure difference across the door. The shape of the downstream door jamb is found to have a considerable influence on the operation of the door at low angles. Removal of the door results in a lower entry mass flow over most of the operating range. It is shown that the mass flow ratio can be predicted quite well from the measured door angles by means of a simple theory.
An Improved Version of the Cebeci-Smith Eddy-Viscosity Model
Authors: Nituch M.J. , Sjolander S. , Head M.R. 
Published: July 2016

SummaryAlthough the Cebeci-Smith method of calculating turbulent boundary layers is widely used and generally gives acceptably accurate results, highly inaccurate skin-friction values are obtained for relaxing flows and equilibrium layers in strong adverse pressure gradient. In the present paper, these anomalies are removed by suitable modifications to the basic eddy-viscosity model.
A Surface Source and Vorticity Panel Method
Authors: Petrie J.A.H. 
Published: July 2016

SummaryA panel method for solving potential flow problems of arbitrary geometry is presented. It is very easy to apply and should be very quick to run. Unlike most other panel methods this one does not require a specification of the vorticity distribution in advance, but obtains it as part of the solution. The method is applied to three test cases chosen for their difficult and varied nature.
Vortex Shedding from Smooth and Roughened Cylinders in Cross-Flow near a Plane Surface
Authors: Buresti G. , Lanciotti A. 
Published: July 2016

SummaryThe characteristics of the flow field around a circular cylinder in cross-flow placed at various distances from a plane, parallel both to the flow and to the cylinder axis, were analysed using a hot wire anemometer. Experiments were performed in a wind tunnel with Reynolds numbers ranging from 0.85×105to 3×105. The spectra of the hot wire signals were obtained using a Fast Fourier Transform technique programmed on a PDP 11/40 computer. As regards a smooth cylinder, the main features of the vortex shedding mechanism in the subcritical regime remained unaltered for distances from the plane greater than approximately 0.4 diameters; in particular the Strouhal frequency did not show any significant variation relative to the typical value for an isolated cylinder. As for lower values of the distance from the plane, the regular vortex shedding disappeared and the hot wire spectra showed typical turbulent features. The possibility of obtaining supercritical conditions by roughening the cylinder surface was confirmed together with the importance of the Reynolds number based on the typical roughness size, Rk, in the evaluation of the flow regime around the cylinder. In the case of roughened cylinders, and with values of Rkbelow-350, the regular vortex shedding disappeared at a distance from the plane smaller than 0.3 diameters. This fact suggests that, at least in part of the supercritical regime, the influence of the plane can be smaller than in the subcritical regime.
Aerodynamic Interaction Between Two Spheres at Reynolds Numbers Around 104
Authors: Lee K.C. 
Published: July 2016

SummaryThe behaviour of streams of solid particles when ejected into a fluid crossflow suggests that there are considerable forces caused by aerodynamic interaction between closely spaced particles. The overall effect is a dispersion of the solids normal to the fluid flow direction and a bunching up along the axis. This effect is apparent in aerial work where particulate solids are released from aircraft and also in dilute two phase flow especially at the onset of choking or saltation. The experimental work reported here contrives to measure these forces for spheres at the appropriate Reynolds numbers. The results are considered to be sufficiently accurate and comprehensive to give some understanding of the phenomena occurring and to permit an explanation, at least qualitatively, of the behaviour mentioned.
Aerodynamics of Airfoils with Porous Trailing Edges
Authors: Ventres C. Samuel , Barakat Richard 
Published: July 2016

SummaryThe aerodynamics of a thin airfoil of arbitrary camber having a porous trailing edge in steady, subsonic, compressible potential flow is investigated. In the special case of a flat plate airfoil with a porous trailing edge, an exact, closed form solution is obtained using complex variable theory. The pressure loading on the airfoil, the lift and pitching moments are exhibited explicitly along with typical numerical results. The corresponding situation in supersonic flow is also considered.
Incompressible Flow Past a Wing-Body Combination Using General Curvilinear Coordinates
Authors: Murray J.C. 
Published: July 2016

SummaryIt is shown, by the successive application of coordinate transformations involving complex analytic functions, how a general curvilinear coordinate system can be constructed which is suitable for geometries consisting of a finite surface together with two semi-infinite cylinders. A typical example of such a geometry is considered which comprises a wing-body combination in which two semi-infinite unswept wings are attached to a finite body. The potential problem associated with non-lifting incompressible flow past the wing-body combination is formulated in the general curvilinear coordinate system and is solved numerically. The distribution of the pressure coefficient over the wing-body surface is presented.
Pressure Gradient and Leading Edge Effects on the Corner Boundary Layer
Authors: Zamir M. , Young A.D. 
Published: July 2016

SummaryResults are presented of velocity and pressure measurements made in the initially laminar boundary layer in a streamwise corner formed by two flat plates at 90° to each other set at various incidences. The leading edges of the plates were sharp in contrast to earlier tests with an aerofoil type leading edge. It was found impossible to obtain a steady enough flow for useful measurements to be made at zero incidence and pressure gradient, a small incidence associated with a favourable pressure gradient was necessary. This is believed to be because of the development of separation bubbles at the sharp leading edge at very small incidences due to small variations of flow direction to be expected in a wind tunnel. The profiled nose used in earlier tests afforded flow conditions much closer to the ideal theoretical model involving zero pressure gradient, but it is argued that any nose however shaped may introduce disturbances in the form of characteristic secondary flows that may well determine the downstream response of the boundary layer. In any case the corner flow is highly unstable at all but very low Reynolds numbers, and in the absence of a region of favourable pressure gradient a Reynolds number in terms of distance downstream of the leading edge greater than about 105is unlikely to be attained in practice with the flow remaining smooth and laminar.
Linear Stability of a Radial Wall Jet
Authors: Tsuji Y , Morikawa Y 
Published: July 2016

SummaryA linear stability analysis was made for a radial wall jet. A perturbation method against the two-dimensional wall jet was used for the formulation, from which a non-homogeneous Orr-Sommerfeld equation was derived. The computation showed that disturbances are more unstable in the radial wall jet than in the two-dimensional case, which agrees qualitatively with an experimental evidence.
Influence of the Wake Component on Turbulent Skin Friction at Subsonic and Supersonic Speeds
Authors: Mabey D.G. 
Published: July 2016

SummarySome velocity profile and skin friction measurements for turbulent boundary layers at subsonic and supersonic speeds are reviewed to derive the magnitude of the wake component and the effects of its variation with Reynolds number on predictions of skin friction. As Reynolds number increases the wake component increases rapidly, reaches a maximum and then decreases. The measurements considered suggest that this maximum may be higher at supersonic speeds than at subsonic speeds. This wake component variation has a significant influence on predictions of skin friction in the Reynolds number range of interest on wind tunnel models.
Calculation of Subsonic Normal Force and Centre of Pressure Position of Bodies of Revolution Using a Slender Body Theory – Boundary Layer Method
Authors: Thomson K.D. 
Published: July 2016

SummaryThe aim of this paper is to present a method for predicting the aerodynamic characteristics of slender bodies of revolution at small incidence, under flow conditions such that the boundary layer is turbulent. Firstly a panel method based on slender body theory is developed and used to calculate the surface velocity distribution on the body at zero incidence. Secondly this velocity distribution is used in conjunction with an existing boundary layer estimation method to calculate the growth of boundary layer displacement thickness which is added to the body to produce the effective aerodynamic profile. Finally, recourse is again made to slender body theory to calculate the normal force curve slope and centre of pressure position of the effective aerodynamic profile. Comparisons made between predictions and experiment for a number of slender bodies extending from highly boattailed configurations to ogive-cylinders, and covering a large range of boundary layer growth rates, indicate that the method is useful for missile design purposes.
Design of Aerofoils for Prescribed Pressure Distribution in Viscous Incompressible Flows
Authors: Dutt H.N.V. , Sreekanth A.K. 
Published: July 2016

SummaryA design procedure has been developed to generate aerofoil shapes for prescribed pressure distributions in an incompressible viscous attached flow. It is based on the method of singularities, originally proposed by Chen and later modified by Kennedy and Marsden, for inviscid flows. The classical approach of adding the displacement thickness of the boundary layer and wake to the aerofoil contour is used to account for viscous effects. Several numerical examples are worked out and are compared with the inviscid flow results. Significant changes in aerofoil contours due to viscous effects are observed and these are discussed.
The Pressure Distribution on the Surface of an Ellipsoid in Inviscid Flow
Authors: Band Edward G.U. , Payne Peter R. 
Published: July 2016

SummaryThe classic equations for inviscid flow about an ellipsoid are employed to compute the corresponding static pressure distribution which can then be applied to a number of practical problems. The tension in the skin of a dirigible, the gross pressure distribution around a man in an open ejection seat, the aerodynamic lift on an air cushion vehicle, automobile or high speed boat, the “squatting” of a ship, are all examples of practical applications. A remarkable result from the theory is that the lowest pressure, that around the equator normal to the flow, is always constant around the equator, no matter how much disparity there is between the semi-axes b and c.
Re-Circulating Flows Associated with Two-Dimensional Steps
Authors: Moss W.D. , Baker S. 
Published: July 2016

SummaryThis paper describes measurements made in the regions of separated flow associated with three simple sharpedged two-dimensional geometries, a rear-facing step, a front-facing step and a rectangular block. The use of the pulsed-wire anemometer made possible the measurement of the three components of mean velocity and turbulence; earlier techniques, such as the hot-wire anemometer, were not well suited to the accurate determination of these quantities either in regions of continually reversing flows such as the re-circulatory zone or in regions of very high turbulence such as the shear layers bounding these zones. Supplementary measurements of surface pressure and shear stresses are also presented and comparison is made between these shear layers and the plane mixing layer. The work forms the first part of an extended programme for the investigation of bluff body flows but its principal immediate value will probably help in providing data with which to test the validity of mathematical models of turbulence as applied to re-circulating flows.
An Investigation of Turbulent Boundary Layer on a Flat Plate With a Small Step Change in Surface Roughness
Authors: Narayana P.A. Aswatha 
Published: July 2016

SummaryThe response of turbulent boundary layer to sudden change in surface roughness have been studied experimentally. Mean velocity measurements have been made in the boundary layer on a flat plate, downstream of a small step change in surface roughness under 3 different pressure gradients. The surface upstream of the step consisted of ‘k* type ‘large roughness’ wall (or ‘small roughness’ wall) and downstream of the step consisted of smooth surface (or ‘small roughness’ wall). Velocity profiles after the step change have been analysed on the basis of the two layer model. The inner region responds very quickly to the new boundary condition while the outer region takes more time to attain equilibrium or a state of local self-preservation. The skin-friction coefficient initially increased after the step change and gradually reached towards a constant value except for a particular roughness combination under adverse pressure gradient wherein the change in the roughness function is gradual over the transition.
Non-Equilibrium Flow of an Ideal Dissociating Gas Behind an Attached Shock Wave
Authors: Sharma V.D. 
Published: July 2016

SummaryThe curvature of an attached shock wave and the flow variable gradients at the tip of a straight edged wedge caused by non-equilibrium effects are determined for a steady plane flow. The specific source of non-equilibrium effects considered here is the dissociation-recombination reaction in a symmetrical diatomic gas. An oxygen like idea dissociating gas is used as an example in calculating the desired quantities. The qualitative behaviour of the exact results is compared with those obtained by using approximate methods.
Miniature Pressure Probe for Measuring the Surface-Shear-Stress Vector in Turbulent Flow
Authors: Pontikos N. , Bradshaw P. 
Published: July 2016

SummaryIf two small fences are arranged approximately at right angles in plan view, the magnitude and direction of surface shear stress can be deduced from measurements of the pressure difference across each fence. Fence heights as small as 0.05 mm are easily achieved. The device is simpler to use than null-seeking arrangements, and is accurate even in the presence of strong pressure gradients, which are shown to have large effects on other types of surface obstacle in three-dimensional flow.