bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Transformation of Aerodynamic Stability Derivatives by Symbolic Mathematical Computation
Authors: Howard James C 
Published: July 2016

SummaryThe formulation of mathematical models of aeronautical systems for simulation or other purposes, involves the transformation of aerodynamic stability derivatives. It is shown that these derivatives transform like the components of a second order tensor having one index of covariance and one index of contravariance. Moreover, due to the equivalence of covariant and contravariant transformations in orthogonal Cartesian systems of coordinates, the transformations can be treated as doubly covariant or doubly contravariant, if this simplifies the formulation. It is shown that the tensor properties of these derivatives can be used to facilitate their transformation by symbolic mathematical computation, and the use of digital computers equipped with formula manipulation compilers. When the tensor transformations are mechanised in the manner described, man-hours are saved and the errors to which human operators are prone can be avoided.
The Three-Shock Confluence Problem for Normally Impinging, Overexpanded Jets
Authors: Kalghatgi G T , Hunt B L 
Published: July 2016

SummaryIn this paper, a systematic study of the triple shock confluence point is presented for the case of an overexpanded jet which impinges on a perpendicular flat plate at small displacements from the nozzle. The jet is uniform upstream of the free jet shock wave. Non-homentropic effects are taken into account and lead to modifications to the accepted flow patterns at a triple point for the case of strong incident shock waves. Where more than one thermodynamically possible solution to the triple point equations exists, the alternative solutions are re-examined, taking non-homentropic effects into consideration. Some discussion of the possibility of infinite shock curvatures is also included. Qualitative flow patterns of the impinging flow are constructed, based on the triple point solutions and the known boundary conditions. The interesting cases where the tail shock flow is supersonic are given particular attention and two possible flow patterns are distinguished. Finally, some experimental evidence in the form of schlieren pictures is presented. Although not conclusive, this evidence supports the theory.
Inviscid Hypersonic Source Flow, over Slender Power-Law Bodies
Authors: Yasuhara M , Watanabe S 
Published: July 2016

SummaryHypersonic small-disturbance theory is applied to the source flow over power-law slender bodies with conical or wedge type asymptote. The results for a point source flow with λ=2 over power-law cones of revolution show that the dominating equations in the first and second approximations are essentially the same as the ones for the parallel flow over power-law bodies of revolution. In the special case of a cone, results of a source flow and of a parallel flow are compared and it is shown that the surface pressure in a source flow at the nose is the same as the constant cone pressure in a parallel flow, but systematically decreases in the rear part. This is confirmed by comparison with a shock tunnel experiment.
Hole Reinforcement in Isotropic and Orthotropic Plates Using Filament-wound Discs
Authors: McKenzie D O , Webber J P H 
Published: July 2016

SummaryA theoretical and experimental study is made of the stresses and strains around circular holes in plates reinforced with carbon fibre filament-wound discs. An analytical solution is given for infinite isotropic plates subjected to uniform tension, but for orthotropic carbon fibre plates the finite-element displacement method of analysis is used. The filament-wound discs are found to be efficient in reducing the stresses around the holes with the principal stresses being taken, in the main, by the strong fibres. There is reasonable agreement with the experimental results for the uniform tension cases, but results from tests on bolt-loaded holes do not correlate as well with theory.
A New Exact Solution for Compressible Swirling Flow
Authors: Greitzer E M 
Published: July 2016

SummaryAn exact analytic solution is presented for axisymmetric compressible swirling flow in an annular passage. The solution is given in terms of simple expressions for the streamline shapes. The results can be used to describe an irrotational flow as well as a class of rotational flows in annular passages, such as might be encountered in turbomachinery components. The solution could be applied as a test case for numerical computations of flows in turbomachines.
Flow Regimes over Delta Wings at Supersonic and Hypersonic Speeds
Authors: Squire L C 
Published: July 2016

SummaryThis paper concerns the boundaries between flow regimes for sharp-edged delta wings in supersonic flow and the relation of some predictions of thin-shock-layer theory to these boundaries. In particular, it is shown that the theory predicts that the attachment lines on the lower surface of a thin delta wing at supersonic speeds suddenly jump from just inboard of the leading edges to the centre line in certain flight conditions. In general there is close agreement between the conditions for this jump and the flight conditions corresponding to the change-over from attached flow to the leading-edge separation on the upper surface. Since the movement of the attachment lines on the lower surface must change the position of the sonic line and the nature of the expansion around the edge, it is suggested that the two phenomena are directly related. Thus thin-shock-layer theory can be used to establish the boundaries of the various flow regimes for a wide range of Mach number, incidence and wing sweep. The theory can also be used to predict the effects of wing thickness on leading-edge separation, but here the experimental data is very sparse and somewhat contradictory, so the value of the prediction in the case of thickness requires further investigation.
Some Notes on Coleman Instability
Authors: Simpson A 
Published: July 2016

SummaryThe equations of motion of a highly idealised model of a helicopter with a simple lag-hinged rotor are derived by Lagrange’s method. It is shown that the transformed equations governing Coleman instability (ground resonance) have a regular form involving wholly symmetric and skew-symmetric matrices. The work input to the unstable motions derives wholly from the torque applied to the rotor by the engine, but the torque equation is superfluous as far as the eigenvalues are concerned. Approximate stability criteria show that chassis and lag dampingsper seare destabilising relative to the undamped reference condition and can lead to a substantial lowering of the critical rotor speed for instability onset. A necessary condition for instability (dynamic) is that two eigenvalues of thestiffnessmatrix are simultaneously negative.
Supersonic Flow Past a Slender Delta Wing. An Experimental Investigation Covering the Incidence Range –5° ≤ α ≤ 50°
Authors: Richards I C 
Published: July 2016

SummaryA detailed survey of a delta wing of 70° sweep has been performed at M = 2.5. The measurements include upper- and lower-surface pressure distributions, schlieren photographs, vapour-screen photographs and surface oil-flow visualisation. The results have been compared with thin-shock-layer theory and various other predictions.
The Origin and Nature of the Lift Force on the Leeward of Two Bluff Bodies
Authors: Price S J 
Published: July 2016

SummaryThis paper deals with the force coefficients on the leeward of two bluff bodies, in particular with the origin and nature of the lift force. Initially a general description of the characteristics of the force coefficients, plus the effect of parameters such as free-stream turbulence and surface roughness in the form of stranding, is given.A resume of all the known suggestions for the origin of the lift force is listed and a series of experiments, attempting to test these suggestions using simple methods, is described. These methods consist mainly of force measurement, involving force measurement on the leeward conductor using different shapes for the leeward and windward bodies. However, static pressure tapping and flow visualisation are also employed to a small degree.It is shown that none of the suggestions gives a satisfactory explanation for the origin of the lift force. However, several interesting points were noted; for instance the dependence of the lift profiles for the leeward body on its own characteristics in the wake and not particularly on the wake characteristics. Hence it is shown that the use of wake parameters, measured without the presence of the leeward body when attempting to assess the forces thereon, is an over-simplification of the situation as far as lift is concerned while appearing to work quite well for drag.
The Occurrence of Stagnation Bubbles in Supersonic Jet Impingement Flows
Authors: Kalghatgi G T , Hunt B L 
Published: July 2016

SummaryThis paper reports an experimental investigation into the stagnation bubbles found in the shock layers of some supersonic jets impinging on perpendicular flat plates at small nozzle-to-plate distances. The experiments used twelve contoured nozzles within the Mach number range 1.42 to 2.83. Surface pressures were measured on the plate and free-jet pitot pressure distributions were obtained at the level of the centre of the plate shock. Schlieren pictures were taken of both impinging and free jets. It was found that the bubbles result from the interaction of the plate shock with very weak shock waves which are produced in the jet either by small imperfections in the nozzle wall or by slight inaccuracies in the design or production of the nozzle contour. The bubbles can be eliminated by suitable improvements to the nozzle. Other anomalous flows produced by shock interactions are described and explanations offered. It is shown that the bubbles sometimes encountered at close plate spacings with conical nozzles are also due to shock waves. However, for wide-angled nozzles, internal shocks can be an inherent part of the flow from the nozzle and the bubbles which they produce are thus an inherent part of the impingement flow. From physical arguments concerning the main factors involved in producing a bubble, a parameter is constructed whose values are shown to be a good criterion for whether a bubble occurs or not.
Supersonic Cone with Surface Blowing
Authors: Carafoli E , Berbente C 
Published: July 2016

SummaryThe velocity field around a circular cone in supersonic flow is determined by considering fluid injection and suction through the porous wall of the body. By using a new method of linearisation of the equations of motion, analytical formulae are obtained which yield almost exact results, as compared with numerical calculations. In addition, the method proposed suggests new problems related to fluid injection and suction which are important for practical applications.
Post-Buckling Behaviour of Simply-Supported Cross-Ply Rectangular Plates
Authors: Prabhakara M K 
Published: July 2016

SummaryAn analysis is presented for the post-buckling behaviour of simply-supported, laminated cross-ply rectangular plates subjected to biaxial compression. The solution to von Kármán-type large deflection equations of the plate is expressed as a double sine series for the transverse deflection and a double series of clamped-clamped beam functions for the force function. All the boundary conditions, including those involving the normal bending moment at the edges, are satisfied exactly. The series solution is found to converge rapidly. Using only the first few terms in the series, numerical results for square graphite-epoxy unsymmetric laminates under uniaxial compression is presented graphically.
The Confluence of Three Shock Waves in Three-Dimensional Flow
Authors: Hunt B.L. , Lamont P.J. 
Published: July 2016

SummaryThis paper presents a theoretical study of the confluence of three shock waves in three-dimensional flow. A suitable transformation reduces the problem to that of a planar confluence point for which the theory already exists. Expressions relating the two flows are developed and successfully applied to an experimentally observed intersection. It is found that the three-dimensional flow can have an entirely supersonic downstream flow, unlike its two-dimensional counterpart, and that the flows in the two downstream regions need not be parallel.
Effects of Stream Turbulence on Free Shear Flows
Authors: Patel Rajni P. 
Published: July 2016

SummaryRecently attention has been given to the effects of the stream turbulence on the characteristics of the turbulent boundary layers and the turbulent shear flows. For the boundary layers considerable information on the effects of the stream turbulence is available but for the shear flows it is limited. This paper describes an experimental investigation for the effects of stream turbulence on the development of an asymmetric jet and a plane mixing layer. It is shown that the characteristics of these flows are considerably affected by the stream turbulence but for the measurements in the plane mixing layers at large downstream distances the influence of the stream turbulence is negligible provided the intensities are less than 0.6%. For the plane mixing layer the results show that the flow characteristics are not affected significantly by the initial boundary layers, the acoustic disturbances and the boundary conditions imposed by the end plates.
The Attachment of a Ventilated Plane Jet to an Inclined Plane Wall
Authors: Marsters G.F. 
Published: July 2016

SummaryThe behaviour of a plane jet issuing in the neighbourhood of a plane wall has been studied experimentally. Such arrangements may find application in jet augmented flaps for STOL aircraft development. The essential features of this configuration are the gap between the wall and the jet nozzle, permitting entrainment of secondary flow, and the inclination of the plane wall with respect to the nozzle axis.Measurements of velocity profiles, wall static pressure distributions and turbulence intensities reveal the presence of extensive regions of low pressure over the wall, strong pressure gradients resulting in the highly curved flow, a fair degree of self-preservation of the mean velocities, but no particularly unusual features observed in the turbulence quantities. The size of the gap, the wall angle and the wall length all influence the reattachment location, and limits of gap, angle and length for which reattachment occurs are shown. The sub-ambient static pressure regions give rise to significant forces on the wall; these forces are primarily due to the entrainment feature.
Buckling of Simply Supported Orthotropic Skew Plates
Authors: Kennedy J.B. , Prabhakara M.K. 
Published: July 2016

SummaryA double Fourier series solution is presented for the buckling of simply supported orthotropic and isotropic skew plates, subjected to in-plane compressive and shear edge loads. All the boundary conditions, including the vanishing of the normal bending moment along the edges, are satisfied. Numerical results, suitable for design purposes, are presented graphically for a number of independent parameters such as skew angle, ratio of flexural rigidities and aspect ratio. The results show that the buckling strength is substantially effected by the skew angle, and to a lesser extent, by the ratio of the flexural rigidities and aspect ratio. In contrast with positive shear edge loads, which tend to decrease the skew angle, negative shear edge loads appear to reduce the buckling strength of orthotropic and isotropic skew plates.
Some Low Speed Experimental Results on the Effects of Swirl and Velocity Distribution on an Axi-Symmetric Jet
Authors: Young A.D. , Rao K.N. 
Published: July 2016

SummaryThe flows resulting from a number of different methods for producing swirl in an axi-symmetric jet have been investigated. These methods include upstream vanes, tangential injection, a twisted plastic sheet and rotation of part of the jet pipe. Tests were also made with the first two types of swirl device in association with a radial distribution of axial velocity in the jet which had a minimum on the axis produced by a suitably graded wire grid or web inserted in the jet pipe. The measurements covered the mean (axial and swirl) velocity distributions as well as the main turbulence quantities at various stations downstream of the jet exit. It was found that the swirl considerably enhanced the rate of growth of the mixing region as previous workers have shown, but there was a significant reduction of this enhancement when the axial velocity increased from the centre outwards. This is in accordance with current concepts on the stability of curved turbulent shear flows.
Hypersonic Flow Over Conical Wing-Body Combinations
Authors: Hillier R. 
Published: July 2016

SummaryThis paper shows how thin shock layer theory may be applied to wing-body combinations and also to yawed wings of caret and diamond section. The common feature of these cases is the interaction of the crossflow with the body slope discontinuity and the manner in which the resulting disturbances propagate through the shock layer. Practical computation of surface pressures is straightforward and comparison with experiment appears to be fairly good for the limited results available.
The Effect of Chordwise Flexibility on the Lift of a Rapidly Accelerated Airfoil
Authors: Katz J. , Weihs D. 
Published: July 2016

SummaryThe effects of finite chordwise flexibility on the development of lift on a rapidly started airfoil are studied. This is a generalization of the so-called Wagner problem of unsteady aerodynamics. It is found that the lift varies with time in a non-monotonous fashion, including more than one extremum. The lift at large times is found to be lower, the more flexible the foil. Changes in the wake vortex sheet are also discussed.
Effect of Base Cavities on the Aerodynamic Drag of an Axisymmetric Cylinder
Authors: Morel Thomas 
Published: July 2016

SummaryBase cavities (hollow extensions mounted behind the rear end of a bluff body) are known to reduce substantially the aerodynamic drag of two-dimensional bodies. For axisymmetric bodies their effect is not well established, and the objective of this work was to assess their drag-reducing potential. Experiments were performed using three different types of base cavities, one solid walled and two ventilated, each with six different depths ranging from 0.1 to 0.9 body diameters. All three types of cavities reduced the body drag for small cavity depths, with a maximum drag coefficient reduction of 0.027 being obtained with a ventilated cavity 0.2 diameters deep. The reductions are an order of magnitude lower than those reported for two-dimensional bodies, but are achieved with a much shorter cavity depth. Although the ventilated cavities had a beneficial effect for small depths, at large depths (greater than 0.5 diameters) they had an opposite effect – a very large drag increase. The cause of this increase is as yet not understood. Hot-wire investigation revealed that base cavities suppress wake periodicity. For cavities of small depth this correlated with a reduction in drag, but for large cavity depths the trends of the intensity of the periodic motion and of drag were not always the same.
The Fibre Composite Helicopter Blade
Authors: Mansfield E.H. , Sobey A.J. 
Published: July 2016

SummaryIn Part 1 expressions are derived for the coupled torsional, extensional and flexural stiffnesses of a fibre composite tube, such as a helicopter blade, which is subjected to torsion, longitudinal tension, chordwise and flapping bending moments and shear. The theory is an extension of Batho-Bredt engineering analysis and is valid for a cylindrical tube of arbitrary cross-section with an arbitrary circumferential distribution of fibre composite plies. Particular attention is paid to the coupling effects in which an asymmetric fibre lay-up results in a twisting of the tube under bending and/or tension. Consideration is also given to the influence on the stiffness characteristics of an initial twist in the tube.In Part 2 the analysis of Part 1 is developed numerically for tubes representative of GFRP blades. Static and dynamic aspects are considered which pave the way for aeroelastic tailoring studies of such blades.
Shockwave and Boundary Layer Interaction in the Presence of an Expansion Corner
Authors: Chew Y.T. 
Published: July 2016

SummaryAn investigation has been carried out to examine one aspect of supersonic jet-engine inlet flow, namely shock-wave and boundary-layer interaction in the presence of an expansion corner. The experiment was undertaken at Mach numbers of 1.8 and 2.5. The local Reynolds number per metre varied from 2.79 to 3.13 × 107 for M = 1.8 and from 4.20 to 6.4-8 × 107 for M = 2.5. Adiabatic turbulent boundary layers of about 6 mm thick on an expansion-corner plate were disturbed at different streamwise positions by oblique shocks with deflection angles of 4°, 6° and 8°. The pressure distributions, wave patterns and the extent of the separation regions were strongly influenced by the presence of the expansion corner, especially when the shock impingement positions were upstream of the corner. The pressure rise induced by the incident shock began to decrease in level when the shock impingement position was about 3-4 boundary-layer thicknesses upstream of the corner. As the incident shock moved towards the corner, the pressure rise and the extent of the separation region decreased. When the shock impingement position was at the corner, the reflected shock was effectively neutralised by the Prandtl-Meyer expansion; especially when the deflection angle of incident shock matched that of the expansion corner. The three dimensionality of the incident shock and separation region is due to the interactions between the glancing oblique incident shock and the tunnel’s sidewall boundary layers.
Transition in the Infinite Swept Attachment Line Boundary Layer
Authors: Poll D.I.A. 
Published: July 2016

SummaryThe transition behaviour of the boundary layer which is formed along an infinite swept attachment line has been studied experimentally. Circular trip wires and turbulent flat plate boundary layers have been used as sources of disturbance and the range of parameters covered has been such that the results are directly applicable to full scale flight conditions. Simple criteria have been deduced which allow the state of the boundary layer to be determined for given geometric and free stream properties. Sample calculations for typical swept wing configurations suggest that the majority of civil aircraft will have turbulent attachment lines in the cruise and that subsequent relaminarisation in regions of favourable pressure gradient is unlikely.
A Simplified Theory of Oscillating Aerofoils in Transonic Flow: Review and Extension
Authors: Dowell E.H. 
Published: July 2016

SummarySignificant new results are presented to show to what extent a simplified theory for transonic flow may be used. Solutions are obtained by classical techniques and compared with experiment. Results are given for two-dimensional and three-dimensional, steady and unsteady flow. The effects of flow separation and improvements in Bernoulli’s equation and the surface boundary condition are also briefly discussed.