bluuebunny/crossref_metadata_2025 huggingface dataset:
Theoretical and experimental investigations on an active control system for vertical fin buffeting alleviation using strain actuation
Authors: F. Nitzsche  , S. Liberatore  , D. G. Zimcik
Published: July 2016

In the present investigation, the results obtained during the ground vibration tests of a closed-loop control system conducted on a full-scale fighter to attenuate vertical fin buffeting response using strain actuation are presented. The experimental results are supported by numerical analyses using a finite element aeroelastic model of the structure. Two groups of actuators consisting of piezoelectric elements distributed over the structure were designed to achieve authority over the first and second modes of the vertical fin. The control laws were synthesised using the linear quadratic Gaussian (LQG) method for a time-invariant two-input, two-output (2x2 MIMO) control system. Three different pairs of sensors including strain gauges and accelerometers at different locations were used to close the feedback loop. The results demonstrated that actual reductions of up to 18% in the root-mean-square (RMS) values of the fin dynamic response measured by the strain transducer at the critical point for fatigue at the root were achieved for the second mode under the most severe buffet condition.
Future challenges for powerplant aerodynamic integration in combat aircraft
Authors: Philpot M. G.
Published: July 2016

The operational requirements of modern combat aircraft demand complex engine intake and exhaust systems, capable of working efficiently over a very wide range of flight conditions and throttle settings. In addition to high aerodynamic efficiency and avoidance of high distortion levels at the engine face, these systems must also meet rigorous radar and infra-red signature targets. This paper discusses the implications from the aerodynamics point of view. Examples of technical approaches which seek to balance the sometimes conflicting requirements of aerodynamics and signatures are outlined. The potential offered by in-flight thrust vectoring to enhance flight performance and/or safety is also reviewed and the aerodynamic implications considered. Overall, propulsion integration for combat aircraft presents several challenges to the aerodynamicist, not least the development and validation of improved theoretical design methods capable of analysing the highly complex flows involved.
Performance enhancement evaluation of an actuated trailing edge flap
Authors: Chan W. , Brocklehurst A.
Published: July 2016

An analytical evaluation of the performance enhancement due to a servo-actuated trailing edge flap was carried out using the coupled rotor-fuselage model (CRFM). The performance enhancement from a trailing edge flap is achieved by introducing effective camber around the azimuth for a nominal aerofoil. An investigation on the best combination of flap parameters, namely the span, position, chord and deflection was carried out in order to identify an optimal configuration within given design constraints. The effects on vibratory control loads over a range of speed for a flap of 10% span, 20% chord, actuated at once per rev has expanded the retreating blade envelope for a Lynx aircraft by some 20kt. The flap hinge load was also examined and it was found not to be excessive. It was also confirmed that an actuated trailing edge flap does not have adverse effect on the pilot's control inputs to trim to a particular flight condition. This paper will discuss the aerodynamic enhancements derived from the application of the trailing edge flap and present conclusions drawn from this study.
Numerical and experimental investigations of air-jet vortex generators in streamwise pressure gradients
Authors: Lewington N. P. , Henry F. S. , Peake D. J. , Singh C.
Published: July 2016

Numerical and experimental results are presented demonstrating the sensitivity of the performance of air-jet vortex generators (AJVGs) operating at jet to freestream velocity ratios of up to 4 to jet pitch and jet skew. The merits of installing co- or counter-rotational systems are shown. Numerical results for AJVG arrays on a flat plate in a zero pressure gradient indicate optimum values for jet spacing and velocity ratios to enhance the downstream skin friction above the uncontrolled value. The installation of a co-rotating array of AJVGs into a modified NACA 23012 unswept wing and the improvements in the lift and drag performance are illustrated. It is demonstrated that by careful implementation of boundary conditions in relatively straightforward ‘numerical’ experiments it is possible to carry out a sensitivity analysis on the vortex generator arrays before they are implemented in successfully enhancing wing performance.
Characterisation of the realistic impact threat from runway debris
Authors: Greenhalgh E. S. , Chichester G. A. F. , Mew A. , Slade M. , Bowen R.
Published: July 2016

This paper describes a study to characterise the impact threat to aircraft from runway debris. This work investigated the likelihood of an event exceeding a critical impact energy; it did not address the probability of an event occurring. Runway debris was collected from six airfields and parameters such as size fraction, mass, density, bluntness and material type were characterised. The distribution of the stone mass against frequency was accurately modelled and based on this, an expression was developed for the probability of an impact exceeding a critical level during a single take-off or landing. By considering the probability of a 50J impact from runway debris as a once in a lifetime event, the implication is that the actual threat is significantly more than the currently perceived threat. This study provides the foundations for more comprehensive studies and will give the designers improved understanding of the threat to aircraft from runway debris.
Numerical and experimental investigations on the reduction of wind tunnel wall interference by means of adaptive slots
Authors: Meyer O. , Nitsche W. , Futterer I.
Published: July 2016

The flow in many wind tunnel experiments is affected by the presence of test section walls. The resulting interference can be minimised by correcting the measured model pressures, or by influencing the model flow directly with the use of ventilated or adaptive test section walls. The objective behind the latter technique is to guide the flow in the test section to achieve low interference (i.e. free flow) condition at the model. The most successful technique of flexible, adaptive walls is still restricted to small research wind tunnels due to its mechanical complexity. However, a very promising alternative is the use of adaptive slots in the test section walls. This concept combines the method of passive slotted walls, as they are already implemented in many large wind tunnels, and flexible walls. Additionally, this technique presents the opportunity of full 3D adaptations because the slots can be situated in all four test section walls.

This paper presents preliminary experimental results and the latest numerical calculations on the effectiveness of adaptive slots. The experiments were conducted under high subsonic flow conditions in the new slotted test section of the transonic wind tunnel at TU Berlin’s Aeronautical Institute (ILR).

The numerical results presented are focussed on the 2D slot adaptation of a 2D-model (CAST7 aerofoil) and the 3D slot adaptation of a body of revolution (3D-ETB). In addition, basic studies were made of the flows associated with a single slot on one wall and a bump on the other.

The numerical and the first experimental investigations have shown the potential of adaptive slots to reduce wall interferences effectively. The adaptation accuracy of the investigated slot configurations deviated not more than 3% from the reference case (2D-wall adaptation).
Potential fuel savings due to hybrid laminar flow control under operational conditions
Authors: Young T. M. , Fielding J. P.
Published: July 2016

Hybrid laminar flow control (HLFC) is an active drag reduction technique that permits extended laminar flow on an aircraft surface and thus offers the potential for significant fuel savings. This is at the expense of an increase in system weight and specific fuel consumption. An overview of HLFC system failure types and consequences is presented as an introduction to this study, which investigated the impact of a potential loss of laminar flow due to flight in cirrus clouds. At typical cruising altitudes, the ice crystals are of a sufficient size and may result in sufficient particle flux to cause a temporary transition of the boundary layer. A computer performance model of a twin engine aircraft in the class of the Boeing 757 has been used to study the impact of alternative fuel planning scenarios on the fuel consumed by a HLFC aircraft, taking into account a model of probable cloud encounter. Based on the models, the study showed that if the fuel planning assumed 25% time-in-cloud (TIC) during the cruise, then in the extreme case of 55% TIC during the cruise, the contingency fuel (taken as 3% of the trip fuel), would be sufficient for the aircraft to complete the mission (including the alternate leg and hold).
Saving costs in design, manufacturing and operation of aero engine parts
Authors: Broede J.
Published: July 2016

Basic requirements for aero engine parts are to carry loads at high temperatures safely over service periods of 30-40 years. This generally calls for the best and latest materials and for highly sophisticated design and manufacturing procedures.

These requirements are frequently in contrast to the desire to keep costs at affordable levels. This aims at the costs at both the customer’s side as well as the manufacturer’s side. The measures to reduce cost in the design and production phase are various:

• redesign to allow for less complex manufacturing processes

• reassessment of quality characteristics without reduction of overall quality (only those characteristics to be maintained which are really critical)

• acceptance of minor damage in new parts which would be acceptable for repaired parts according to technical standards

• assessment of all steps in the production process with respect to their influence on the final product properties

• more stabilised manufacturing processes which use only a portion of accepted tolerance bands to reduce the subsequent test effort

• change of material.

In the service phase, cost reduction can be achieved by optimum exploitation of part’s life potential. The means are improvement of the lifing concepts where portions of the crack propagation life may be utilised in addition to the traditionally cleared crack initiation life. Accurate records of life consumption can be obtained with modern systems for life usage monitoring.
Hypersonic missiles — some problem areas
Authors: East R. A. , Edwards J. A.
Published: July 2016

An overview of some of the problems, which have to be overcome in the design of hypersonic missiles or projectiles, is given. In the main, these are connected with the high levels of heat transfer rate suffered by such vehicles, particularly those induced by aerodynamic control surfaces. Some of the aspects of heat transfer, induced by, and suffered by such controls are presented. Data are presented and discussed, regarding the effects of flow separation due to flaps or flares, the effects of sharp and bluff fins (both swept and unswept). Finally, the aerodynamic interactions and heat transfer rates induced by reaction control jets are presented.
Inflight icing data gathering during routine flight operations — a case study
Authors: Brown A. P.
Published: July 2016

For the purpose of the design and certification of inflight icing protection systems for transport and general aviation aircraft, the eventual re-definition/expansion of the icing environment of FAR 25/JAR 25, Appendix C is under consideration. Such a re-definition will be aided by gathering as much inflight icing event data as reasonably possible, from widely-different geographic locations. The results of a 12-month pilot programme of icing event data gathering are presented. Using non-instrumented turboprop aircraft flying upon mid-altitude routine air transport operations, the programme has gathered observational data from across the British Isles and central France. By observing a number of metrics, notably windscreen lower-corner ice impingement limits, against an opposing corner vortex-flow, supported by wing leading edge impingement limits, the observed icing events have been classified as ‘small’, ‘medium’ or ‘large’ droplet. Using the guidance of droplet trajectory modelling, MVD values for the three droplet size bins have been conjectured to be 15, 40 and 80mm. Hence, the ‘large’ droplet category would be in exceedance of FAR/JAR 25, Appendix C.

Data sets of 117 winter-season and 55 summer-season icing events have been statistically analysed. As defined above, the data sets include 11 winter and five summer large droplet icing encounters. Icing events included ‘sandpaper’ icing from short-duration ‘large’ droplets, and a singular ridge formation icing event in ‘large’ droplet. The frequency of ‘large’ droplet icing events amounted to 1 in 20 flight hours in winter and 1 in 35 flight hours in summer. These figures reflect ‘large’ droplet icing encounter probabilities perhaps substantially greater than previously considered. The ‘large’ droplet events were quite localised, mean scale-size being about 6nm.
Multigrid acceleration of an upwind Euler method for hovering rotor flows
Authors: Allen C. B.
Published: July 2016

The effect of multigrid acceleration implemented within an upwind-biased Euler method for hovering rotor flows is presented. The requirement to capture the vortical wake development over several turns means a long numerical integration time is required for hovering rotors, and the solution (wake) away from the blade is significant. Furthermore, the flow in the region near the blade root is effectively incompressible. Hence, the solution evolution and convergence is different to a fixed wing case where convergence depends primarily on propagating errors away from the surface as quickly as possible, and multigrid acceleration is shown to be less effective for hovering rotor flows. It is found that a simple V-cycle is the most effective, smoothing in the decreasing mesh density direction only, with a relaxed trilinear prolongation operator. Results are presented for multigrid computations with 2, 3, 4, and 5 mesh levels, and a CPU reduction of approximately 80% is demonstrated for five mesh levels.
Kite equilibrium and bridle length
Authors: Alexander K. , Stevenson J.
Published: July 2016

Kite design has recently seen a revival, with sports such as kite buggying and kite surfing becoming significant businesses in some countries. Since the aerodynamics of kites has not been explored in much depth this paper sets out to explain a major behaviour of kites, predicting where they will settle during flight. The analysis is confined to a vertical plane containing the kite string. It examines the basic forces for single-line or two-line kites and shows how the line azimuth angle(s) and equilibrium settling point(s) can be derived from the aerodynamic properties of the kite, from the kite mass and from the bridle lengths. It is noted that while several equilibrium points are predicted not all are stable equilibrium points. Wind tunnel tests with a specially built rigid model are described and these are shown to confirm theoretical predictions.
Numerical studies of infrared signature levels of complete aircraft
Authors: Mahulikar S. P. , Sane S. K. , Gaitonde U. N. , Marathe A. G.
Published: July 2016

This paper begins with an outline of the procedure for predicting the infrared signature emissions from the airframe, engine casing, and the plume, and their attenuation by the intervening atmosphere. These emissions are contrasted against the background, to obtain the infrared signature levels. The infrared detector’s — noise equivalent flux density, is proposed as an operational constraint on the flight envelope. The shift of this newly imposed constraint on the flight envelope for several engine-operating conditions, and for turbojet and turbofan engines is studied. The signature levels from the casing and plume, of a turbofan and equivalent turbojet engine, are compared at different operating points on the flight envelope. Result in the form of a polar plot of infrared signature level variation with aspect is also examined for low flying missions. The results are analysed to direct stealth design and operation.
Some aspects of the flow in S-shaped diffusing ducts
Authors: Yu S. C. M. , Goldsmith E. L.
Published: July 2016

The circular cross-sectional Royal Aerospace Establishment (RAE) 2129 S-shaped intake diffusing duct series, shown in Fig. 1, which has an offset of the inlet and exit centerline of 0·3 and 0·45 of the axial length of the duct, was designed at the RAE (Bedford) and tested at British Aerospace Filton, at low forward speeds (freestream Mach no. range from 0 – 0·2 but a range of duct inlet Mach numbers up to choking speeds) in the last two decades to fulfil the objectives of collecting systematic experimental data on engine face pressure recovery, total pressure flow distortion and wall static pressures for computational fluid dynamics validation. Some of the measurements have been presented, as for example, by Willmer, Brown & Goldsmith. The measurements from one version of Model 2129 (the 0·3 length offset S-duct geometry) have been used to compare with calculated results from a number of CFD programs, as for example, by Anderson, Horton and by the AGARD Working Group 13. The series of comparison also highlight the need for measurements other than the engine face total pressure and wall static pressure which have already been made.
Compact analytic solutions for a decaying, precessing circular orbit
Authors: McInnes C.R.
Published: July 2016

The evolution of low Earth orbit satellites under the action of atmospheric drag and J2 oblateness perturbations has been widely investigated. Simple analyses describing the altitude decay of a circular orbit through energy arguments have also been widely available. This paper extends these simple analyses by providing compact analytic expressions for true anomaly and ascending node angle along with a more accurate expression for altitude decay. The resulting solutions then allow a fast and efficient method of investigating the orbital evolution of decaying, precessing circular orbits. Applications include the rapid evaluation of station-keeping budgets for both single platforms and the orbital evolution of satellite constellations. Passive station-keeping by continuous low thrust acceleration is investigated and shown to be naturally unstable.
An experimental study of dynamic stall on a finite wing
Authors: Coton F. N. , Galbraith R. A. McD.
Published: July 2016

This paper examines the dynamic stalling of a finite wing of aspect ratio 3·0 when subject to constant pitch motions up to and beyond stall. In particular, unsteady surface pressure data were obtained at 192 locations on the wing surface and these were then analysed to provide information on the nature and phasing of dynamic stall events in both the chordwise and spanwise directions. It was also possible to obtain sectional force and moment coefficients by integration of the pressures measured on specific chordal arrays. This provided valuable insight into the load distribution on the wing throughout the range of motion. On this basis, it was established that the wing loading distribution was consistent with conventional understanding of steady wing loading up to the incidence at which the dynamic stall vortex was initiated. Beyond this point, the formation and subsequent convection of the vortex structure was found to be strongly three-dimensional but, nevertheless, exhibited many of the features of two-dimensional dynamic stall.
Induced drag prediction for wing-tail and canard configurations through numerical optimisation
Authors: Lombardi G. , Vicini A.
Published: July 2016

A computational procedure has been developed in order to predict aerodynamic interference between lifting surfaces, and to devise configurations which best meet given aerodynamic requirements. The procedure, which couples an aerodynamic solver with a numerical optimisation routine, is useful in the preliminary design of aircraft. The essential features of the aerodynamic code and of the optimisation routine are described, along with the coupling criteria. Some of the most significant predictions obtained in induced-drag minimisation for wing-tail and canard configurations are described and discussed.
Some reflections on trends in rotorcraft technology and configurations — into the 21st century
Authors: Balmford D.E.H.
Published: July 2016

This series of lectures recalls the achievements of that outstanding pioneer of rotary wing flight Juan de la Cierva. At around the age of 23, he began to develop the concept of improved safety in flying machines, and included in his studies the concept of the helicopter. Having carried out many tests of various possible configurations, he discarded the concept of true helicopter flight as not being achievable with the then current state-of-the-art.

However, he became convinced that his basic objectives of short takeoff and landing, and safe low speed flight could be achieved by replacing the wing of a conventional aircraft with an autorotating rotor.
Project review — do you really know where you are?
Authors: Balthazor L. R.
Published: July 2016

Project reviews are carried out to enable the right decisions to be taken to achieve project objectives. However, these decisions are often taken on incomplete, optimistic, inaccurate, misleading or simply wrong information. Whilst incompleteness is inevitable with the complex and rapidly changing nature of high technology engineering projects, it is important that the project manager has a good appreciation of the extent to which these other factors may affect the progress information upon which judgements are made. This paper explores a few of the traps the author has come across, and suggests possible approaches to avoid some of them.

A systems perspective is recommended, with a focus on risk management, resolving ambiguity, rapid response, trend analysis, earned value principles and taking account of the effects of organisational changes.
The Superorbital Expansion Tube concept, experiment and analysis
Authors: Neely A. J. , Morgan R. G.
Published: July 2016

In response to the need for ground testing facilities for super orbital re-entry research, a small scale facility has been set up at the University of Queensland to demonstrate the Superorbital Expansion Tube concept. This unique device is a free piston driven, triple diaphragm, impulse shock facility which uses the enthalpy multiplication mechanism of the unsteady expansion process and the addition of a secondary shock driver to further heat the driver gas. The pilot facility has been operated to produce quasi-steady test flows in air with shock velocities in excess of 13 km/s and with a usable test flow duration of the order of 15 μs. An experimental condition produced in the facility with total enthalpy of 108 MJ/kg and a total pressure of 335 MPa is reported. A simple analytical flow model which accounts for non-ideal rupture of the light tertiary diaphragm and the resulting entropy increase in the test gas is discussed. It is shown that equilibrium calculations more accurately model the unsteady expansion process than calculations assuming frozen chemistry. This is because the high enthalpy flows produced in the facility can only be achieved if the chemical energy stored in the test flow during shock heating of the test gas is partially returned to the flow during the process of unsteady expansion. Measurements of heat transfer rates to a flat plate demonstrate the usability of the test flow for aerothermodynamic testing and comparison of these rates with empirical calculations confirms the usable accuracy of the flow model.
An experimental study of transition and the development of turbulence in a linearly retarded boundary-layer flow
Authors: van Oudheusden B. W.
Published: July 2016

An experimental investigation was carried out of the incompressible boundary layer flow along a flat plate, in the presence of an adverse pressure gradient that corresponds to a linear retardation of the free stream velocity. The turbulence level in the free-stream was 0·12% and transition occurred with the laminar boundary layer being close to separation. For three values of the Reynolds number (2·56, 3·11 and 4·09 million based on the reference length that is defined as the reciprocal of the nondimensional-velocity gradient) the laminar, transitional and turbulent regions were studied by single (normal) hot-wire surveys at several streamwise positions. This allows the fluctuations of the streamwise velocity component to be followed from the amplification of laminar instability waves, through breakdown in the intermittency region, and the subsequent development towards a more or less developed turbulence structure. The study reveals that within the transition region fluctuation levels are reached throughout a large part of the boundary layer that are significantly higher than those in fully developed turbulent flow, which is partly a direct consequence of the intermittent character of the flow. For the highest Reynolds number additional cross-wire surveys were carried out in the turbulent region to observe the development of the turbulent stresses following transition. The data are interpreted in terms of structural coefficients, eddy viscosity and mixing length. Also, these results indicate that the transition process can be associated with turbulence levels well in excess of those occurring in fully developed turbulence, and reveal the relaxation of the outer region turbulence structure.
An introductory guide to literature in aeroelasticity
Authors: Battoo R. S.
Published: July 2016

This paper is meant primarily for non-specialist readers who may not be familiar with aeroelasticity. The main objective is to direct the reader to some important texts and papers that have been published in the areas which embrace aeroelasticity, from which the reader may gain sufficient knowledge about the subject. Since aeroelasticity is a large field which requires considerable knowledge in several related areas newcomers can often be daunted by the subject. This is further compounded by the great amount of published material available. This paper will assist the reader to locate key publications and help identify major works which have been useful in studying the subject. A comprehensive list of references is included which will help to identify key subject areas, researchers, research establishments and publications for further study.
Energy partitioning in high speed impact of analogue solid rocket motors
Authors: Schonberg W. P.
Published: July 2016

Modelling the response of solid rocket motors to bullet and fragment impacts is a high priority among the military services from standpoints of both safety and mission effectiveness. Considerable effort is being devoted to characterising the bullet and fragment vulnerability of solid rocket motors, and to developing solid rocket motor case technologies for preventing or lessening the violent responses of rocket motors to these impact loadings. Because full-scale tests are costly, fast-running analytical methods are required to characterise the response of solid rocket motors to ballistic impact hazards. In this study, a theoretical first-principles-based model is developed to determine the partitioning of the kinetic energy of an impacting projectile among various solid rocket motor failure modes. Failure modes considered in the analyses include case perforation, case delamination, and fragmentation of the propellant simulant material. Energies involved in material fragmentation are calculated using a fragmentation scheme based on a procedure developed in a previous impact study utilising propellant simulant material. The model is found to be capable of predicting a variety of response characteristics for analogue solid rocket motors under high speed projectile impact that are consistent with observed response characteristics. Suggestions are made for improving the model and extending its applicability to a wider class of impact scenarios.
Cone cavity flow at M = 8·2 with injection of air and helium
Authors: Bellone F. , Stollery J. L.
Published: July 2016

An experimental investigation of cone cavity flow at M = 8·2 with injection of air and helium has been performed in the Cranfield University gun tunnel. The cone used had a 10° semi-angle and incorporated an annular cavity. The boundary layer ahead of the cavity was laminar. The study concentrated on the effects of increasing the mass injected into the cavity.

With no injection the external flow bridged the cavity. A shock wave and a pressure peak occurred at the rear face corner. By injecting gas, this pressure peak was decreased in intensity and a shock wave was formed at the front face corner. As the mass injected was increased, the shocks initially formed at the front and rear face corners were shifted upstream from their initial positions and boundary layer separation occurred ahead of the cavity. For the highest mass flow rate injected, the pressure peak at the rear face corner was very small. The cavity flow was never more than mildly unsteady.
A Technical Note on the appropriate CFD boundary conditions for the prediction of ground effect aerodynamics
Authors: Barber T. J. , Leonardi E. , Archer R. D.
Published: July 2016

The accurate prediction of ground effect aerodynamics is an important aspect of wing-in-ground effect vehicle (WIG) design. Computational fluid dynamics (CFD) solutions are useful alternatives to expensive (especially in the case of ground effect) wind-tunnel testing. However, the incorporation of the rigid surface effects often leads to confusion due to such a model being in a vehicle fixed reference frame (air moving, vehicle fixed) rather than the real-life situation of a ground fixed reference frame (air fixed, vehicle moving).
The role of modelling and simulation in the development of advanced non-destructive evaluation systems
Authors: Generazio E. R. , Harris C. E.
Published: July 2016

Non-destructive evaluation (NDE) technologies are a critical component of a collaborative engineering environment. The role of NDE simulations in component design, manufacturing, certification, integrity and repair are identified and discussed in the context of a futuristic intelligent synthesis environment (ISE) that facilitates collaborative engineering. Each of these critical areas needs to be simulated in a virtual reality environment and is expected to have a large effect on the cost, life, safety, and risk of aerospace products. In a collaborative engineering environment, NDE simulations will provide ‘real-time’ feedback to component designers and systems engineers. This feedback is necessary to achieve optimum overall system-level benefits.
A statistical analysis of the surface pressure distribution on a delta wing
Authors: Jupp M. L. , Coton F. N. , Green R. B.
Published: July 2016

This paper describes and presents results from static wind tunnel tests conducted on a 60° delta wing at a root chord Reynolds number of 2·7 x 106. In these tests, the wing was instrumented with 192 miniature pressure transducers which, in conjunction with a powerful multi-channel data-logging system, allowed the distribution of time-varying surface pressures to be measured at high temporal resolution. Analysis indicates that the distribution of root mean square pressure on the leeward surface of the wing can provide considerable insight into the behaviour of both the primary and secondary vortex structures. In addition, it has been established that the frequency content of pressure signals measured in the vicinity of these vortex structures is sensitive to the vortex state. It is suggested that these data features can be directly attributed to previously observed behavioral characteristics of the vortex breakdown process.
A new induced-drag prediction method using Oswatitsch’s expression
Authors: Veilleux C. , Masson C. , Paraschivoiu I.
Published: July 2016

This paper presents a critical study related to the evaluation and breakdown of total wing drag based on solutions of the Euler equations for subsonic and transonic three-dimensional flows.

This study clearly identifies the false entropy production present in all discretised Euler solutions as the main source of the discrepancies between the drag predictions produced by body-surface pressure integrations and far-field methods. A good understanding of the entropy production mechanisms present in discretised threedimensional Euler solutions has lead to an original procedure for the total drag breakdown and a new method for the evaluation of the induced drag. This new technique is based on body-surface pressure integrations and Oswatitsch’s expression integrated over suitable integration surfaces. In contrast with the various methods for the drag breakdown and the evaluation of the induced drag available in the literature, the proposed technique uses an exact formulation and is simple to implement. Using detailed drag calculations on an elliptic wing (theXt= 1·0 wing) and the ONERA M6 wing, it has been shown that this new technique is not strongly sensitive to grid refinement and to the level of false entropy production in the calculation domain.
Vulnerability prediction method for use in aircraft conceptual design
Authors: Al-Ahmed S. , Fielding J. P.
Published: July 2016

A methodology has been developed to integrate the vulnerability discipline into the conceptual/preliminary design process of combat aircraft. An interactive and programmable solid modelling Computer Aided Design (CAD) system is used to generate a CAD solid model of the aircraft’s critical components. The aircraft’s components’ sizes and shapes are pre-defined by a conceptual/preliminary design synthesis computer model. A systematic Child-Parent assembly process is used to model the aircraft vulnerability, by defining the criticality degree of each component in the aircraft assembly. Solid Modelling CAD techniques have been modified to develop techniques to perform the two main standard vulnerability assessments, namely the shotline and vulnerable area methods.
Pressure over a dual-cavity cascade at supersonic speeds
Authors: Zhang X. , Edwards J. A.
Published: July 2016

Pressure distributions over a dual cavity cascade were studied at supersonic speeds of Mach 1·5 and 2·5. The study was performed through numerical modelling and results compared with model measurements. The Reynolds-averaged Navier-Stokes equations were solved using a finite-volume algorithm in which the inviscid cell interface fluxes were estimated using Roe's approximate Riemann solver with a second-order extension, and turbulence was modelled using a two-equationk-mmodel with compressibility corrections. Two test configurations were selected: (1) a length-to-depth ratioL/D =1 cavity followed by anotherL/D= 1 cavity, and (2) anL/D= 3 cavity followed by anL/D =1 cavity. The prediction was compared with that of a single cavity of the sameL/D.It was found that the pressure field around theL/D =1 cavity was substantially modified by a precedingL/D =3 cavity. Changes in the pressure and pressure drag coefficient were observed. The study clarified some earlier observations of unsteady modes over a dual cavity cascade, and confirmed model measurements of the pressure fluctuation under a number of flow and geometry conditions.
Wavelet analysis of pilot workload in helicopter low-level flying tasks
Authors: Jones J. G. , Padfield G. D. , Charlton M. T.
Published: July 2016

As part of a programme of research to improve mission effectiveness by studying pilot workload and task performance in mission-oriented flight tasks, a methodology has been developed in which wavelet analysis is used to extract information from records of vehicle response and of pilot control activity. By decomposing the records into discrete wavelets, components of vehicle agility and pilot workload are derived in the form of wavelet-based ‘quickness’ parameters for vehicle agility and so-called ‘attack’ parameters for pilot workload. It is shown how individual wavelet components in the records of pilot control activity, referred to as ‘worklets', can be associated with the sub-tasks of ‘guidance’ and ‘stabilisation'. It is demonstrated how these concepts can be applied to quantify changes in pilot control activity associated with increasing task difficulty or changes in aircraft handling qualities. Two examples are presented, one from a flight trial in which the task difficulty was increased by changes in a prescribed ground track and the other from a simulation trial in which an increased time delay was introduced into the response of the flight control system.
Experimental investigation into transonic flows over tandem cavities
Authors: Taborda N. , Bray D. , Knowles K.
Published: July 2016

An experimental study was conducted to analyse the pressure distribution along the floor of a cavity, with and without the presence of an upstream tandem cavity, at a constant freestream Mach number of about 0-911. Measurements were made for single cavities and the results compared with those obtained in the presence of an upstream tandem cavity. This comparison was made over a wide range of geometries, covering open to closed classes of cavities with both identical and different dimensions for the two cavities. The effect of the spacing between the two cavities was also studied. The downstream cavity is shown to be significantly affected by the presence of an upstream cavity, with both the overall net static pressure and its gradient being affected, dependent upon the class of cavity geometry and spacing under consideration.
Flow regimes associated with yawed rectangular cavities
Authors: Czech M. , Savory E. , Toy N. , Mavrides T.
Published: July 2016

The present work is concerned with the aerodynamics of the turbulent boundary-layer flow over yawed rectangular cavities with the focus on the steady and unsteady pressures generated by the interaction. Cavities with a planform aspect ratio of 4-85 and streamwise length to depth ratios from 1 to 3 were studied experimentally in a low-speed wind tunnel.

The results indicated three main types of cavity flows. The shear layer bridges the cavity for small angles between mean flow direction and minor cavity axis. The flow field remains almost two-dimensional with little change in drag coefficient. Strong instabilities, associated with a rise in drag coefficient, are found when the cavity is yawed to greater angles. An aerodynamic feedback mechanism depending on interactions between the separated shear layer and the cavity fluid is suggested as the mechanism responsible for the generated oscillations. The influence of the cavity depth is, hereby, found to be fundamental as it determines the degree to which interactions between the separated shear layer and the cavity base occur. As a result both the magnitude and the frequency of the instabilities are a function of the cavity depth. When rotating to higher angles a greater portion of the shear layer reattaches to the cavity base which leads to a loss of flow organisation and a significant increase in drag.
Energy requirements for the flight of micro air vehicles
Authors: Woods M. I. , Henderson J. F. , Lock G. D.
Published: July 2016

This paper describes power requirements for micro air vehicles, flying in the Reynolds number regime of -lO*. Three flight modes have been researched: fixed wing, rotary wing and flapping wing. For each mode, the literature in the public domain has been reviewed to obtain appropriate lift and drag coefficient data at these low Reynolds numbers. Energy and power requirements for the three flight modes have been calculated and an optimisation procedure has been utilised to evaluate the most efficient flight mode and configuration for a variety of specified missions. The effect of wind-speed on the optimal solution has been examined. It has been discovered that when there is no hover requirement, fixed wing flight is always most energy efficient for the micro air vehicle. However, if there is a hover requirement, the suitability of flapping or rotary wing flight is dependent on the mission profile and ambient windspeed.
Development and application of farfield drag extraction techniques for complex viscous flows
Authors: Hunt D. L
Published: July 2016

A new method for deriving the components of drag from the CFD solution of an aircraft flowfield, by analysis of its wake, is presented. This method is applied to viscous flow calculations. It is also applied to configurations containing powerplants. The drag values predicted by this method are compared with the values obtained using more traditional methods, and good agreement is demonstrated.
Assessment of turbulence model performance for transonic flow over an axisymmetric bump
Authors: Hasan R. G. M. , McGuirk J. J.
Published: July 2016

A computational study has been performed to evaluate the predictive capabilities of some existing eddy-viscosity (both linear, LEVM, and non-linear, NLEVM) and Reynolds stress transport turbulence models (RSTM) by reference to a transonic shock-induced separated flow over a 10% axisymmetric bump. The calculations have been carried out during the course of a collaborative research programme including both UK universities and industry. The findings of the project demonstrate that improved results can be obtained for such flows by using more advanced turbulence models. For linear eddy-viscosity models, only the SST approach gave good predictions of shock location, recirculation size and pressure recovery, although this was accompanied by deficiencies in the prediction of post-shock velocity profile shape. Non-linear eddy-viscosity models, particularly at the cubic level, provided a more consistent level of agreement with experiments over the range of shock location, wall pressure and velocity profile parameters. Some improvement was also seen in the prediction of turbulence quantities, although only a move to an RSTM closure model reproduced the measured peak stress levels accurately. It was notable that the use of low-Re variants of the models (instead of wall functions) produced no significant improvement in predictions. There are, however, some shortcomings in all models, particularly in the development of flow after reattachment, which was always predicted to be too slow.
Lord Kings Norton — his contribution to the gas turbine aero engine
Authors: Evans Mike
Published: July 2016

The twentieth century has seen man’s mastery of the air, and fundamental to that achievement has been the provision of power to sustain the process of flight. For the first forty years the piston engine reigned supreme, yet for even longer now the power to fly has been provided by the gas turbine. In the conception and development of this prime mover Britain can justly claim to have led the world.

Two servants of the Crown quite independently had the vision and that amalgam of creative and analytical powers to see what might lie beyond the piston engine — one a scientific civil servant working at the Royal Aircraft Establishment (RAE) and the other, remarkably, a young RAF officer already distinguishing himself as a pilot. But the birth of the jet engine proved to be a painful process. While early aircraft designers had embraced the piston engine, neither Government nor the aircraft or aero engine industry showed interest initially in the gas turbine. The change in attitude began when war approached in 1939 and thereafter accelerated in the effort to move from bench demonstrator status to a full-production engine capable of contributing to the outcome of the war. It was in this difficult and complex process of transition that Dr Harold Roxbee Cox — Lord Kings Norton — was to play such a vital role. To appreciate his achievements it is appropriate to remind ourselves of the progress — or lack of it — on the gas turbine prior to his becoming involved.
Lord Kings Norton and the Air Registration Board, Part 2
Authors: Chaplin John
Published: July 2016

The Air Registration Board came into being as a result of the work of the Gorell Committee. It was incorporated in February 1937 and started work on April 1 of that year. The chairman of the board was Sir Maurice Denny, and there was a very small staff— reflecting the limited duties given to it initially. By early 1938 these had grown somewhat — so, for example, the board was authorised to recommend changes to regulations and requirements and it also started to investigate the design of prototype aircraft (cautiously, the Air Ministry limited it to investigations of aircraft weighing less than 10,000lb.).
Absolute Factuality, Common Sense, and Theological Reference in the Thought of Franz Rosenzweig
Authors: Fisher Cass
Published: July 2016

Since its publication, Franz Rosenzweig's magnum opus,The Star of Redemption, has remained a challenge to its readers and a source of wildly conflicting interpretations. It should be a matter of great consternation to Rosenzweig's readers that, shortly after his publication of theStar, he came to identify the work with common sense. This article traces the emergence of common sense within Rosenzweig's thought and undertakes a critical analysis of his use of the term. In contrast to other efforts to address this topic, I argue that Rosenzweig's belated appeal to common sense is a useful heuristic tool for understanding his account of God, the divine-human relationship, and the power and limits of theological language in theStar.
Jonathan Edwards's Reformed Doctrine of Theosis
Authors: Strobel Kyle
Published: July 2016

Amid a scholarly rediscovery of Protestant forms of theosis, questions of whether Jonathan Edwards developed a theotic account of redemption have received increased attention. Ironically, however, interest in Edwards's doctrine of theosis has emphasized the philosophical rather than the theological bases in ways that seem to set him outside the boundaries of Reformed orthodoxy. Yet if we shift our attention away from the neo-Platonic explanations of Edwardsian theosis and place it instead where Edwards himself focused—on the communicable nature of the triune God within the economy—we see that his notions of theosis rest on firmly Protestant foundations and result in recognizably Reformed conclusions. But to say that attention to Edwards's trinitarian and incarnational theology reveals an orthodox form of theosis is not to say that his theotic soteriology lacked distinctive and even innovative elements. Unlike other theologians whose accounts of theosis bifurcated God's communicable nature from the creatures’ relational participation among the divine persons, Edwards's theology made room for and insisted on both.
The Tension between an Eschatological and a Utopic Understanding of Tradition: Tillich, Florovsky, and Congar
Authors: Noble Ivana
Published: July 2016

The theme of this article takes us to the field of ecumenical theology understood as a dialogue between theologians from particular Christian traditions. These theologians relate through their common roots in Scripture and early Christian heritage, but they interpret these roots in their own particular way. In our case the focus will be on the German Lutheran theologian Paul Tillich (1886–1965), the Russian Orthodox theologian George Florovsky (1893–1979), and the French Catholic theologian Yves Congar (1904–1995), who all, at one time, shared the same premises, though not necessarily the same opinions.