Two alternative presentations are given of Patel’s Preston tube calibration. In the first, Δp/τw is tabulated as a function of Δpd2/ρν2; in the second, cf is plotted as a function of Δp/½ρU2 and Ud/ν, so that values of cf, can be read off directly.

Effusion cooling consists in forcing a gas under pressure through a porous material thereby absorbing heat from the material and forming a heat insulating layer on the exposed surface. The internal heat transfer between the porous material and coolant is considered and the heat transfer coefficient obtained from experiment. An approximate analysis for the heat insulating effect based on a heat balance method is derived in detail and applied to experiments with porous plugs set into the side of a duct carrying hot gases, and to porcras cylinders swept by hot gases. It has been found that this analysis applies reasonably accurately to the results of these experiments and of most of the published data. The manufacture of porous materials is discussed briefly and a representative list of commercially available materials is included. The application of effusion and sweat cooling to the blading and combustion chamber linings for gas turbines, rocket motors and the outside skin of flying vehicles is considered.

One of today’s most propitious immersive technologies is virtual reality (VR). This term is colloquially associated with headsets that transport users to a bespoke, built-for-purpose immersive 3D virtual environment. It has given rise to the field of immersive analytics—a new field of research that aims to use immersive technologies for enhancing and empowering data analytics. However, in developing such a new set of tools, one has to ask whether the move from standard hardware setup to a fully immersive 3D environment is justified—both in terms of efficiency and development costs. To this end, in this paper, we present AeroVR—an immersive aerospace design environment with the objective of aiding the component aerodynamic design process by interactively visualizing performance and geometry. We decompose the design of such an environment into function structures, identify the primary and secondary tasks, present an implementation of the system, and verify the interface in terms of usability and expressiveness. We deploy AeroVR on a prototypical design study of a compressor blade for an engine.

A discrete-vortex representation of the wake of a circular cylinder, in which vortices are convected in a potential-flow calculation and maintain their identities unless they approach one another or a surface closely, predicts many of the unsteady flow features and is computationally more efficient than other schemes. The mean rate of shedding of vorticity is adjusted to be compatible with experiments at a high subcritical Reynolds number of 3 × 104 and the model gives reasonable predictions of separation, drag, lift, Strouhal number and vorticity loss in the formation region. The method is extended to accommodate a second cylinder and many of the surprising features which have been observed experimentally with two cylinders in a side-by-side arrangement are reproduced.

Using Rayleigh's principle, the natural frequencies of thin isotropic rhombic plates, with three possible combinations of boundary conditions obtained by combining clamped-clamped and clamped-supported edge conditions, are determined in Part I of this paper. To introduce constant limits of integration, non-orthogonal co-ordinate systems are used and the wave shape for the vibrating plate is approximated by using normal functions representing mode shapes of corresponding bars. To estimate the accuracy of these eigenvalues, Kato's theorem is used and the lower bounds for the natural frequencies are determined in Part II of the paper. It is also shown that normal beam functions are not generally suitable for the determination of eigenfrequencies of skew plates with large skew angles.

Microwaves are a form of electromagnetic radiation commonly used for telecommunications, navigation and food processing. More recently microwave technologies have found applications in fibre-reinforced polymer composites, which are increasingly used in aircraft structures. Microwave energy can be applied with low power (up to milliwatts) for non-destructive testing and high power (up to kilowatts) for heating/curing purposes. The state-of-the-art applications at high power include curing, three-dimensional (3D) printing, joining and recycling, whereas low-power microwave techniques can provide quality checks, strain sensing and damage inspection. Low-power microwave testing has the advantage of being non-contact, there is no need for surface transducers or couplants, it is operator friendly and relatively inexpensive; high-power microwave energy can offer volumetric heating, reduced processing time and energy saving with no ionising hazards. In this paper the recent research progress is reviewed, identifying achievements and challenges. First, the critical electromagnetic properties of composites that are closely related to the heating and sensing performance are discussed. Then, representative case studies are presented. Finally, the trends are outlined, including intelligent/automated inspection and solid-state heating.

The Technology Sub-Group of Air Travel – Greener by Design was instituted at the first full meeting of the GBD community in March 2000. Its first period of intense activity was from the summer of 2000 to the spring of 2001, culminating in the publication of its report The Technology Challenge in July 2001 at the first Air Travel – Greener by Design Conference at the Royal Aeronautical Society.

In the period that followed, the contents of the report were further disseminated by presentations at conferences and publication of the report in The Aeronautical Journal but there was no substantial activity by the Sub-Group as such. In July 2003, a workshop on ‘The Effect of Aviation on the Atmosphere’, was held at St Catherine’s College, Cambridge. This was planned jointly by members of the Sub-Group and of the Centre for Atmospheric Science in the Department of Chemistry at Cambridge and was jointly funded by GBD and the EC project SCENIC. The organisation of events on the day and the collating and editing of the workshop report was done by Dr Helen Rogers of the Centre for Atmospheric Science. The workshop was attended by a broad cross section from the manufacturing and operating industries, government and academia and its report is a valuable summary of current understanding in 2003.

Optimisation of complex systems frequently requires evaluating a computationally expensive high-fidelity function to estimate a system metric of interest. Although design sensitivities may be available through either direct or adjoint methods, the use of formal optimisation methods may remain too costly. Incorporating low-fidelity performance estimates can substantially reduce the cost of the high-fidelity optimisation. In this paper we present a provably convergent multifidelity optimisation method that uses Cokriging Bayesian model calibration and first-order consistent trust regions. The technique is compared with a single-fidelity sequential quadratic programming method and a conventional first-order trust-region method on both a two-dimensional structural optimisation and an aerofoil design problem. In both problems adjoint formulations are used to provide inexpensive sensitivity information.

The problem of the buckling of flat oblique plates (i.e. in the shape of parallelograms) with all edges clamped under a uniform system of stress is considered. An energy method of calculating the critical stresses is developed and applied to the particular case of a clamped oblique plate under uniform compression parallel to two of the sides. Numerical values for the buckling stress coefficient are obtained for plates having acute angles of 60° and 45°, and side ratios varying between 3/5 and 5/3.

The influence of spanwise correlation of fluctuating pressures due to vortex shedding on the total oscillatory loading of a long bluff cylinder in cross-flow is considered. Experimentally determined pressure correlation lengths on a stationary and vibrating cylinder of square cross section are then combined with previously obtained chordwise pressure distributions to demonstrate the amplification of the oscillatory lift on a long bluff cylinder during cross-flow vibrations.

This paper presents performance analysis and design of ducted propellers for lighter-than-air vehicles. High-fidelity computational fluid dynamics simulations were first performed on a detailed model of the propulsor, and the results were in very good agreement with available experimental data. Additional simulations were performed using a simplified geometry, to quantify the effect of the duct and of the blade twist on the propeller performance. It was shown that the duct is particularly effective at low flight speed and that the blades with relatively high twist have better performance over the flight envelope. Design of the optimal twist distribution and of the duct shape was also attempted by coupling the flow solver with a quasi-Newton optimisation method. Flow gradients were computed by solving the discrete adjoint of the Reynolds-averaged Navier-Stokes equations using a fixed-point iteration scheme or a nested Krylov method with deflated restarting. The results show that the ducted propeller propulsive efficiency can be increased by 2%.

Many situations arise in which aerospace structures are subjected to high frequency excitation, in the sense that the wavelength of the induced dynamic response is much shorter than the overall dimensions of the structure. The application of the conventional finite element method to this type of problem faces two difficulties: (i) the short wavelength of the structural deformation requires the use of many elements, which renders the method computationally expensive or even impracticable, and (ii) the response of the structure at high frequencies can be very sensitive to structural detail, and thus response predictions for an ‘ideal’ structure may differ significantly from the performance of the actual system. For a number of years research effort has been directed towards the development of alternative analysis methods for high frequency vibrations, and recent developments in this area are reviewed in the present paper. The methods considered are: (i) hierarchical versions of the finite element method, (ii) the dynamic stiffness method, (iii)periodic structure theory, (iv)statistical energy analysis and (v) wave intensity analysis.

The existing data relating to stresses round pins in holes are reviewed and co-ordinated.

The first part of the paper deals with pins of which the diameter is less than half the plate width and which are no better than a push fit in the hole; the second section deals with larger pins; and the third section deals with interference fit of the smaller pins. The theoretical background is sketched in two appendices, and the results of three series of photoelastic measurements of the effects of clearance of the pin in the hole are described.

Supersonic civil aircraft present a unique noise certification challenge. High specific thrust required for supersonic cruise results in high engine exhaust velocity and high levels of jet noise during take-off. Aerodynamics of thin, low-aspect-ratio wings equipped with relatively simple flap systems deepen the challenge. Advanced noise reduction procedures have been proposed for supersonic aircraft. These procedures promise to reduce certification noise levels, but they may require departures from normal reference procedures defined in noise regulations. The subject of this article is a take-off performance and noise assessment of a notional supersonic business jet. Analytical models of an airframe and a supersonic engine derived from a contemporary subsonic turbofan core are developed. These models are used to predict take-off trajectories and certification noise levels. Results indicate advanced take-off procedures are helpful in reducing noise along lateral sidelines.

The object of this paper is to set down an overall picture of the practical aspects of compressor blade vibration. In doing so it is inevitable that a certain content is effectively a repeat of other people's contributions to the subject. The authors make no apology for this and offer the paper as a "state of the art" as practised at Bristol Siddeley Engines Ltd. In bringing together the many relevant issues of this problem, it is hoped that a useful presentation is obtained.

There is little hesitation in indicating the most obvious and important practical aspect of blade vibration as that of the inherent danger of blade failure and it is known that the axial flow compressor is susceptible to complete failure caused by the fatigue of one blade.

The multi-stage axial flow compressor is a highly complex aerodynamic machine with, its early and late stages required to operate over wide ranges of incidence and Mach number conditions. To some extent, of course, use of variable geometry can reduce this to less taxing proportions. The aerodynamic environment of front stages has broad boundaries somewhat wider than those relating to rear stages, while middle blade rows generally operate under sensibly constant conditions. This diminishing “severity” of operation, front, rear to middle stage blading is not unrelated to the incidence of blade vibration problems which shows a similar pattern.

I would like to add yet another note to those already published on the notions of viscous and hysteretic damping in a simple oscillator. In particular, I would like to hammer a nail into the coffin of the so-called “complex stiffness.“

One of the features which hysteretic damping may be defined to possess is the property that the energy loss per cycle (in sinusoidal motion) is independent of the frequency of oscillation, ω. This property is derived from some experimental evidence. It is shown in Reference 1 that this behaviour is reproduced by the particular integral of the equation

This paper evaluates a time marching simulation method for flutter which is based on a solution of the Euler equations and a linear modal structural model. Jameson’s pseudo time method is used for the time stepping, allowing sequencing errors to be avoided without incurring additional computational cost. Transfinite interpolation of displacements is used for grid regeneration and a constant volume transformation for inter-grid interpolation. The flow pseudo steady state is calculated using an unfactored implicit method which features a Krylov subspace solution of an approximately linearised system. The spatial discretisation is made using Osher’s approximate Riemann solver with MUSCL interpolation. The method is evaluated against available results for the AGARD 445.6 wing. This wing, which is made of laminated mahogany, was tested at NASA Langley in the 1960s and has been the standard test case for simulation methods ever since. The structural model in the current work was built in NASTRAN using homogeneous plate elements. The comparisons show good agreement for the prediction of flutter boundaries. The solution method allows larger time steps to be taken than other methods.

Steady state aerofoil ground effect is studied both numerically and analytically. Discrete vortex and linear vortex panel methods are applied to a parabolic arc and symmetric Joukowski aerofoil, respectively. A single vortex model for the flow over the parabolic arc aerofoil is developed. The single vortex model and other analytical solutions, valid either near or far from the ground, are compared with the numerical results. The numerical results are used to delineate the influences of angle of attack, camber and thickness. For small values of camber and angle of attack, normalised lift is enhanced near the ground and reduced far from it. For a fixed distance above the ground, normalised lift decreases with increasing angle of attack and camber. Thickness reduces lift at all heights above the ground.

An experiment was made on a turbulent boundary layer with adverse and favourable pressure gradients alternating twice along the stream. The most important findings of the present study are as follows. In the region of the adverse pressure gradient downstream of the strong acceleration, an internal boundary layer develops within the boundary layer. In this internal layer large advection of turbulent energy occurs and the flow is locally non-equilibrium even near the wall. As a result the usual logarithmic law and turbulence similarity in the viscous sublayer break down.

This paper presents a methodology for studying the feasibility of stratosphere airship for high altitude long endurance missions and arriving at the baseline specifications of conventional configuration of stratosphere airship, given the performance and operational requirements. Based on this methodology, the AODAP platform (Airship Optimisation Design and Analysis Platform) was developed. Some innovative concepts used in AODAP that are different from previous methods and codes are presented. The shape optimisation of airship was introduced into the design process, and several optimum objectives can be selected including minimum drag, minimum weight and composite objective based on MDO (Multidisciplinary Design Optimisation). The methodology was validated for other design concepts previously developed for similar missions and also was compared to a low altitude vehicle. The baseline specifications of stratosphere airships designed for various shapes using this methodology are presented. The results of sensitivity analyses for a specified airship are discussed, and the sensitivity of airship length with some critical parameters including area density of envelope fabric, area density of solar cell, efficiency of solar cell and efficiency of fuel cell for the specified shape is also provided.