The flow generated by a synthetic jet actuator with a circular orifice is investigated experimentally and computationally. The experimental data and computational predictions are in fair to good agreement with each other and with the theory for a steady turbulent jet. It is found, however, that the synthetic jet establishes itself much more rapidly than the steady jet, primarily because of turbulent dissipation. The oscillatory nature of synthetic jet flow also gives rise to a much greater entrainment of ambient fluid compared with the case of a steady jet. Finally, self-similarity seems to be established when the oscillations introduced by the actuator are reduced to negligible levels.

By means of a broad survey of the developments in aeroelastic science during the past ten years and of comparable developments in associated fields, in so far as they involve elastic deformation, the present paper attempts to show how the individual subjects concerned are developing strong interconnections. At one time the subjects were for the most part regarded as discrete entities; now they are developing into component parts of an integrated whole —the dynamics of a deformable aeroplane.

It is suggested that in the future it may be necessary to discontinue the present methods of treatment of the component subjects as separate, and to adopt a standard method of attack on the problem treated as a unified whole, especially when adequate computational aids become available. A modified approach, involving an arrangement of the subjects in a frequency spectrum, is also discussed. Some speculations on the elastic provisions which may be necessary in the future are included.

Blade-element models are the most common models for the analysis of propeller aerodynamics, performance calculations and propeller design. In spite of their simplicity these models are very efficient and accurate. Blade-element models use the local induced velocities as an input thus they should be combined with another model in order to calculate these induced velocities. Various models are used for the calculation of the induced velocity, where the most popular ones include: momentum, simplified-momentum, lifting-line (prescribed and free wake), and vortex (McCormick and Theodorsen) models. The paper describes the various models, compares their results and discusses the advantages and disadvantages of each one. The results indicate that the Bladeelement/simplified-momentum model offers very good accuracy together with high efficiency. For propeller performance calculations during steady axial flight, where most of the cross-sections do not experience stall, detailed and complicated models for calculating the induced velocities do not show advantages over the simple bladeelement/simplified-momentum model,

The full equations of motion for the flow of a viscous fluid have proved too complicated for any general solution to be obtained. It is to be doubted if, in. the near future, the problem of fluid motion will be solved in a general manner, although solutions for a few special cases may be found. In view of this it is of some value to investigate experimentally certain cases which are likely to prove of mathematical interest at a later date; this paper deals with such a problem. By means of the results obtained experimentally the mathematical analysis may be guided along the right lines and a satisfactory analytical solutioa of the problem be obtained.

The instrument used in exploring the fluid motion has a special interest of its own as it may prove of use in further aerodynamical investigations where the flow is of three–dimensional character. The development of this instrument, and its performance when tested, are described in Part I.

The experiments for the measurement of the forces on the spinning sphere are described in Part II.

Flight tests on the Handley Page suction wing showed that turbulence at the wing root can propagate along the leading edge and cause the whole flow to be turbulent. The flow on the attachment line of a swept wing was studied in a low speed wind tunnel with particular reference to this problem of turbulent contamination.

The critical Reynolds number, RθL, of the attachment-line boundary layer for the spanwise spread of turbulence was found to be about 100 for sweep angles in the range 40°–60°. A device was developed to act as a barrier to the turbulent root flow so that a clean laminar flow could exist outboard. This device was shown to be effective up to an Rθ of at least 170, so that experiments were possible on a laminar boundary layer at Reynolds numbers above the lower critical value. A spark was used to introduce spots of turbulence into the attachment-line boundary layer and the propagation speeds of the leading and trailing edges were measured. The spots expanded, the leading edge moving faster than the trailing edge, at high Reynolds numbers, and contracted at low values.

The behaviour of Tollmien-Schlichting waves was also investigated by exciting the flow with sound emanating from a small hole on the attachment line. Measurements of the perturbation phase and amplitude were made downstream of the source and, although accurate values of wave length and propagation speed could be found, difficulties were experienced in evaluating the amplification ratio. Nevertheless, all small disturbances decayed at a sufficient distance from the source hole up to the highest available Reynolds number of 170.

Two new techniques for estimating aircraft stability and control derivatives (parameters) from flight data using feed forward neural networks are proposed. Both techniques use motion variables and control inputs as the input file, while aerodynamic coefficients are presented as the output file for training a neural network. For the purpose of parameter estimation, the trained neural network is presented with a suitably modified input file, and the corresponding predicted output file of aerodynamic coefficients is obtained. Suitable interpretation and manipulation of such input-output files yields the estimated values of the parameters. The methods are validated first on the simulated flight data and then on real flight data obtained by digitising analogue data from a published report. Results are presented to show how the accuracy of the estimates is affected by the topology of the network, the number of iterations and the intensity of the measurement noise in simulated flight data. One of the significant features of the proposed methods is that they do not require guessing of a reasonable set of starting values of the parameters as a popular parameter estimator like the maximum likelihood method does.

Measurements are presented of total pressure, static pressure, surface shear stress and yaw angle in the flow through several S-shaped ducts, each with a thin turbulent boundary layer at entry. The results show that the region of low total pressure in the exit plane, found by previous workers, is due to expulsion of boundary-layer fluid by a pair of contra-totating vortices in the boundary layer. The generation of these vortices is explained: similarly-produced vortices, with similar effects, occur in some types of wind-tunnel contraction and possibly in other three-dimensional flows.

The solution to the problem of the loading generated on a two-dimensional thin aerofoil by an incompressible flow whose normal velocity component is of the general form exp [i(λx+/μy — ωt)] is calculated. The method used extends the two-dimensional integral equation solution for the induced vorticity by means of a Chebyshev expansion of part of the kernel function. Thin aerofoil approximations are made throughout, but no collocation procedure, as such, is required.

The author presented in his recent main lecture to the Society, “The Computer Shapes the Theory”, a number of novel developments in the matrix displacement method. Since the publication of the lecture and discussion will inevitably be delayed and cannot but illustrate the application of the new ideas on a series of examples, he has been repeatedly urged to summarise some of the more important theoretical contributions in the form of Technical Notes. The first deals with the elasto-plastic analysis, in the presence of strain hardening, of arbitrary three-dimensional configurations. The reader is assumed to be familiar with the corresponding elastic analysis given in refs. 2 and 3, where the medium is represented by a suitable assembly of tetrahedra under constant stress and strain. The corresponding two-dimensional case is investigated on the basis of triangles. Arbitrary anisotropic behaviour and large displacements were also included in refs. 2 and 3.

A method for the calculation of steady or unsteady compressible flows is presented. The procedure, based on a cartesian cut cell approach and multi-dimensional high resolution upwind finite volume scheme, can cope with static or moving body problems having arbitrarily complex geometries. The method is described in two parts. In Part A, we discuss the cartesian cut cell approach and upwind finite volume scheme for static body problems. The method is validated on test problems involving both steady and unsteady compressible flows and then applied to some practical problems. The extension of the method to moving body problems is presented in Part B (pp 57-65).

This paper is the second part of a two-part paper that presents a wide-ranging review of train aerodynamics. Part 1 presented a detailed description of the flow field around the train and identified a number of flow regions. The effect of cross winds and flow confinement was also discussed. Based on this basic understanding, this paper then addresses a number of issues that are of concern in the design and operation of modern trains. These include aerodynamic resistance and energy consumption, aerodynamic loads on trackside structures, the safety of passengers and trackside workers in train slipstreams, the flight of ballast beneath trains, the overturning of trains in high winds and the issues associated with trains passing through tunnels. Brief conclusions are drawn regarding the need to establish a consistent risk based framework for aerodynamic effects.

Propellers are the predominant propulsion source for small unmanned aerial vehicles. At low advance ratios, large sections of the propeller blade can be stalled, and the Reynolds number faced by each blade can be low. This leads to difficulties in modelling propeller performance, as the aerodynamic models coupled with blade element methods usually only provide aerodynamic data for an assumed aerofoil section, for a small angle-of-attack range and for a single Reynolds number, while rotational effects are often ignored. This is specifically important at low advance ratios, and a consistent evaluation of the applicability of various methods to improve aerodynamic modelling is not available. To provide a systematic appraisal, three-dimensional (3D) scanning is used to obtain the aerofoil sections that make up a propeller blade. An aerodynamic database is formed using each extracted aerofoil section, across a wide range of angles of attack and Reynolds numbers. These databases are then modified to include the effects of rotation. When compared with experimental results, significant improvement in modelling accuracy is shown at low advance ratios relative to a generic blade element-momentum model, particularly for smaller propellers. Notably, when considering small propeller performance, efficiency modelling is improved from within 30% relative to experimental data to within 5% with the use of the extended blade element momentum theory method. The results show that combining Viterna and Corrigan flat plate theory with the Corrigan and Schillings stall delay model consistently yields the closest match with experimental data.

Results of an experimental investigation of the distribution of skin friction along the wall of a plane turbulent wall jet are presented. The measurements show that it is possible to describe the variation of skin friction coefficient by a formula similar to the Blasius formula which is based on experimental results of turbulent pipe flow. This is simply achieved by considering the inner layer of fluid between the wall and the position where the velocity is a maximum as a boundary layer with an outer uniform free stream of velocity equal to the local maximum velocity.

Other measurements of velocity distribution indicate that within the experimental range and accuracy, the velocity profiles in the jet are similar and that the rate of change of velocity and width of the jet can be expressed by simple power laws. These results are then partially compared with theory.

Experiments have shown that the drag of a body of revolution with a blunt base can be substantially reduced by mounting behind the body a disc of rather smaller diameter than the body. With a single disc the base drag was reduced by about 35 per cent and with two discs a reduction of 55 per cent was obtained. When the cavity between the body and the best single disc was filled in to form a solid boat-tailed afterbody there was an even greater reduction of drag.

A single disc mounted nearer to the body than the position giving low drag gave a large increase of drag with severely unsteady flow. The nature of the flow in both the low-drag and high-drag régimes is discussed.

Experiments are described on the interaction of the shock wave generated by a wedge in a supersonic wind tunnel with the turbulent boundary layer on the side wall. It is shown that the onset of separation appears to be largely affected by the action of streamwise vorticity in the interaction region. A simple approximate theory based on this concept shows reasonable agreement with the experimental results. Comparisons have been made with two-dimensional interactions of normal shocks and boundary layers, but they did not produce any conclusive results.

The effects of aviation on the environment are becoming increasingly important. The world's airlines already have thousands of aircraft serving the passenger and freight markets and the market demand is still increasing. Unless steps are taken to address the problems created by aircraft noise and emissions, the future progress of the air transport industry will be inhibited.

The seriousness of the topic and the factual nature of the Technology Sub Group report are the reasons why this special issue of The Aeronautical Journal is being devoted to “Greener by Design”. Although the report has been carefully read by a number of people outside the Sub Group, it has not been refereed in the normal way (though a number of minor numerical changes have been made to the tables and text of the original report, partly to correct errors and partly for internal consistency). The reports from the other two Sub Groups, covering operations and market-based options, together with the Summary for Policymakers of the Technology Sub Group, will be issued shortly in a single volume but will not necessarily be published in The Aeronautical Journal.

Laminar separation bubbles formed on NACA 0012 aerofoil near the onset of a stall were investigated to clarify the behaviour of the laminar separation bubble. Measurements were done at a chord Reynolds number of 1·3 × 105. Mean velocity measurements indicate that the long bubble of about 35% chord length is formed at α = 11·5° after the short bubble burst occurred. However, the instantaneous flow visualisation picture indicates that the flow is strongly oscillating at this angle of attack. The phase averaging technique has been applied to analyse this oscillating behaviour. The results indicate that the flow is oscillating between a small separation-reattachment bubble formed near the leading-edge at about a 10% chord length and a large separated region extending over the aerofoil surface. It is suggested that this small separation-reattachment bubble has a similar flow structure to that of the short bubble formed at a lower angle of attack.

In this work a combined analysis of the out-of-plane mechanical and the electromagnetic properties of auxetic re-entrant honeycombs is performed. Experimental and numerical simulations are carried out to evaluate the correlation between the anisotropicity of the transverse mechanical properties (shear and compressive modulus) and the permittivity tensor of auxetic honeycombs. The results are evaluated to assess the feasibility of this kind of cellular solid for electromagnetic absorption and window applications with high structural integrity performance.

A theory of creep buckling is presented in which the instantaneous elastic and plastic deformations following the application of a load, as well as the steady creep deformations, are considered in an approximate manner. Equations are given from which the critical time, that is, the time elapsing between load application and the collapse of the column, can be computed.

Recent developments in delta wing aerodynamics are reviewed. For slender delta wings, recent investigations shed more light on the unsteady aspects of shear-layer structure, vortex core, breakdown and its instabilities. For nonslender delta wings, substantial differences in the structure of vortical flow and breakdown may exist. Vortex interactions are generic to both slender and nonslender wings. Various unsteady flow phenomena may cause buffeting of wings and fins, however, vortex breakdown, vortex shedding, and shear layer reattachment are the most dominant sources. Dynamic response of vortex breakdown over delta wings in unsteady flows can be characterised by large time lags and hysteresis, whose physical mechanisms need further studies. Unusual flow–structure interactions for nonslender wings in the form of self-excited roll oscillations have been observed. Recent experiments showed that substantial lift enhancement is possible on a flexible delta wing.