bluuebunny/crossref_metadata_2025 huggingface dataset:
What price supersonic speed? A design anatomy of supersonic transportation Part 1
Authors: Chudoba B. , Coleman G. , Oza A. , Czysz P. A.
Published: February 2016

The first generation of supersonic commercial transportation has seen three serious attempts to arrive at an economically and environmentally viable aircraft. The US B2707-200/300 design was cancelled early before a prototype could emerge; the Russian Tu-144 design succeeded to become the first supersonic transport but spanned only a few years of restricted airline service; the Anglo-French Concorde endured more than 27 glamorous airline service years until the last of its species was retired on 30 August 2003. This first generation was followed by a second generation of supersonic commercial transport projects in the time period between 1986 until about 1999, designs which did not proceed towards the production hardware stage. This study critically examines the anatomy of two generations of supersonic commercial transport design failures and successes in order to arrive at lessons learned free of ‘wishful thinking’. The design conditions leading to the identification of the product ‘solution space’ for an economically and environmentally acceptable supersonic commercial transport are discussed. Having assembled an understanding of the product metrics valid for supersonic commercial transports, the paper then provides an outlook for the first generation of supersonic corporate and cargo jet projects. This first generation of supersonic business jet (SSBJ) and supersonic cargo jet (SSCJ) projects spans a period of nearly two decades of development, starting from 1988 until today. The present study identifies that the product development metrics of this class of aircraft is radically different compared to the metrics valid for supersonic commercial transports. The challenges in VIP transportation and dedicated freight transportation at supersonic speeds are portrayed leading to two principal trains of thought targeting the development of the first supersonic business jet and/or supersonic cargo jet hardware: the development based on a new airframe, and alternatively the development based on an existing airframe.
Dynamic performance investigations of a turbojet engine using a cross-application visual oriented platform
Authors: Kyprianidis K. G. , Kalfas A. I.
Published: February 2016

This paper presents the development of visual oriented tools for the dynamic performance simulation of a turbojet engine using a cross-application approach. In particular, the study focuses on the feasibility of developing simulation models using different programming environments and linking them together using a popular spreadsheet program. As a result of this effort, a low fidelity cycle program has been created, capable of being integrated with other performance models. The amount of laboratory sessions required for student training during an educational procedure, for example for a course in gas turbine performance simulation, is greatly reduced due to the familiarity of most students with the spreadsheet software. The model results have been validated using commercially available gas turbine simulation software and experimental data from open literature. The most important finding of this study is the capability of the program to link to aircraft performance models and predict the transient working line of the engine for various initial conditions in order to dynamically simulate flight phases including take-off and landing.
Aerodynamic load characterisation of a low speed aerofoil using particle image velocimetry
Authors: van Oudheusden B. W. , Casimiri E. W. F. , Scarano F.
Published: February 2016

Particle image velocimetry (PIV) measurements of the flow around a wing section are employed as a basis for non-intrusive aerodynamic mean loads characterisation, providing sectional lift, drag and pitching moment. The technique relies upon the application of control-volume approaches in combination with the deduction of the pressure from the PIV experimental data through application of the momentum equation. The treatment can also be applied when the flow is unsteady; in that case time-mean loads are obtained from velocity statistics, through the use of Reynolds-averaged formulation of the governing equations. The procedure was applied in the experimental investigation of a NACA 642A015 aerofoil, in which the PIV approach is validated against standard pressure-based methods (surface pressure distribution and wake rake). The chord Reynolds number considered in the investigation ranges between 1 – 7 × 105. In addition, the consistency and potential performance of the method was assessed by means of synthetic velocity field data obtained from a numerical flow simulation.
Whirl flutter analysis of prop-rotors using unsteady aerodynamics reduced-order models
Authors: Gennaretti M. , Greco L.
Published: February 2016

The prediction of this aeroelastic phenomenon is an urgent need of the designer and requires devoted numerical tools. This work examines the influence of the accuracy of the aerodynamic modelling on whirl flutter analysis, with particular attention to those models that can conveniently be applied to preliminary design and control purposes. Considering a simple pylon/prop-rotor structure, the aeroelastic instability boundaries are identified by 2D quasi-steady and 2D unsteady aerodynamics theories, along with a 3D unsteady, potential flow BEM solver. A methodology for deriving reduced-order models from unsteady aerodynamic solutions is used. The numerical investigation highlights that the accuracy of the aerodynamic solver included in the analysis may be of crucial importance. The use of 2D aerodynamic models does not always guarantee conservative stability predictions, and this is particularly true for three-bladed rotors where a fully 3D unsteady solver coupled with a wake alignment algorithm seems to be necessary.
Linear theory of optimum hot air balloon performance – application to Titan
Authors: Lorenz R. D.
Published: February 2016

We develop a simple theory for hot air balloon performance with fixed thermal power and linear heat transfer to the environment, applicable to low-temperature situations such as Titan’s atmosphere. The theory results in a closed-form solution and it is shown that an optimum balloon diameter exists – the maximum payload is achieved when the envelope mass and payload mass are equal. It is also shown simply that the floating mass for a given power has a stronger sensitivity to heat transfer coefficient than to the envelope specific mass. A hot air balloon on Titan with a ~2kW heat source could loft a theoretical maximum payload of ~195kg or ~100kg with appropriate margins.
Transitional separation bubbles and unsteady aspects of aerofoil stall
Authors: Sandham N. D.
Published: February 2016

A time-accurate solution method for the coupled potential flow and integral boundary-layer equations is used to study aerofoils near stall, where laboratory experiments have shown high-amplitude low-frequency oscillations. The laminar-turbulent transition model incorporates an absolute instability formulation, which allows the transition process in separation bubbles to be sustained in the absence of upstream disturbances, in agreement with recent direct numerical simulations. The method is demonstrated to capture large scale flow oscillations with Strouhal numbers and amplitudes comparable to experiments. The success of this particular physical model suggests that bubble bursting is primarily due to a potential-flow/boundary-layer interaction effect, in which relatively simple models of boundary layer transition and turbulence suffice to describe the key phenomena.
A circulation control actuator for flapless flight control
Authors: Cook M. V. , Buonanno A. , Erbslöh S. D.
Published: February 2016

Trailing edge blowing over a Coanda surface has been utilised as a circulation control mechanism for increasing the lift of an aircraft wing. Typically, high energy air is blown from a narrow spanwise slot over the rounded trailing edge of a wing and the air supply is modulated to effect a degree of lift control on the wing. This configuration produces an aerodynamic force in a uni-directional sense only. An alternative novel flow control actuator is described which utilises a simple variable geometry Coanda surface with upper and lower spanwise blowing slots to achieve fully proportional bi-directional control in the manner of a conventional flap. A prototype device has been wind-tunnel tested and is shown to have substantially linear response characteristics and to be as efficient as an equivalent flap surface. The performance of a flow control actuator suitable for small UAV applications is described.
Cold flow analysis of trapped vortex combustor using two equation turbulence models
Authors: Selvaganesh P. , Vengadesan S.
Published: February 2016

A new combustor concept referred as the trapped vortex combustor (TVC) employs a vortex that is trapped inside a cavity to stabilise the flame. The cavity is formed between two axisymmetric disks mounted in tandem. TVC offers many advantages when compared to conventional swirl stabilisers. In the present work, numerical investigation of cold flow (non-reacting) through trapped vortex combustor is performed. The numerical simulation involves passive flow through TVC to obtain an optimum cavity size to trap stable vortices inside the cavity and to observe the important characteristics of TVC. One of the main objectives is to evaluate various two equation turbulence models for the aerodynamic predictions of TVC. Commercial CFD software Fluent is used for the present study. In addition to many models available, Non-linear k-ω and modified k-ω models are incorporated through user defined functions. Results obtained include streamlines, residence time and entrainments for all models. The reattachment length obtained by non-linear k-ω model closely matches with that obtained by DNS in the case of forebody-spindle alone. Non-linear k-ω model alone captures the corner vortices while all the other models failed to capture. From the entrainment characteristics study, it is inferred that the primary air needs to be injected for accommodating the decrease in oxidizer inside the cavity to obtain better performance from the TVC.
An investigation into supersonic shallow swept cavity flows
Authors: Reim B. , Panetta C. , Samanes E. , Gai S. , Milthorpe J. , Kleine H.
Published: February 2016

An experimental investigation was conducted to determine the flow characteristics of shallow swept cavities at a free-stream Mach number of 2. The investigation described herein focused on obtaining information on both time-averaged and time-dependent flow features. The data consisted of steady and unsteady pressure measurements as well as some surface oil and schlieren flow visualisation. The effective length-to-depth ratiosl/dof cavities investigated ranged between 5·65 and 8 for shallow ‘open’ cavities and between 11·31 and 16 for ‘closed’ cavities. The cavity sweep angles were 0°, 15° and 45°. The results of the swept cavities, when compared to the datum cases of the straight (0°) cavities, showed some distinct differences. With regard to time-averaged flow characteristics, in an open swept cavity (5·65 <l/d< 8), the flow displayed quasi-open flow behaviour, distorted by the spanwise cross flow within the cavity. In the case of the closed swept cavity (11·31 <l/d< 16), flow features resembling the ‘closed’ to ‘transitional closed’ cavity flow types were seen to exist simultaneously across the span. Unsteady pressure data indicated that for an open cavity at 15° sweep angle, the discrete frequencies observed were similar to those of a straight open cavity. In contrast to this, at 45° sweep angle, the frequencies were broadband with no discrete frequency across the cavity length. For the closed cavity, the frequencies were all broadband irrespective of the sweep angle. The investigation also showed that the influence of the sweep angle on the pressure drag of the cavity strongly depends on the type of cavity flow: a sweep angle increase from 0° to 45° approximately doubled the pressure drag for an open cavity, while it led to a drag reduction of about 37% for the closed cavity.
Convergence: Commodity flight simulation and the future
Authors: Takeda K. , Newman S. J. , Kenny J. , Zyskowski M.
Published: February 2016

The development of commodity flight simulation, in the form of PC game technology, continues to advance at a rapid pace. Indeed, the software industry is now being driven primarily by the requirements of gaming, digital media, and other entertainment applications. This has largely been due to the commoditisation of computer hardware, which is apparent when considering recent trends in central processing unit and graphics processor development.

The flight simulation industry has benefited from this trend of hardware commoditisation, and will continue to do so for the foreseeable future. It is, however, yet to fully realise the potential for leveraging commodity-off-the-shelf (COTS) software. In this paper the opportunities presenting themselves for the next 25 years of flight simulation are discussed, as the aviation and games software industry’s requirements converge. A SWOT (strengths-weaknesses-opportunities-threats) analysis of the commodity flight simulation software industry is presented, including flight modelling, scenery generation, multiplayer technology, artificial intelligence, mission planning, and event handling. Issues such as data portability, economics, licensing, intellectual-property, interoperability, developer extensibility, robustness, qualification, and maintainability are addressed.

Microsoft Flight Simulator is used as a case study of how commodity flight simulation has been extended to include extensive programmatic access to its core engine. Examples are given on how the base platform of this application can be extended by third-party developers and the power this extensibility model provides to the industry.

This paper is presented to highlight particular technology trends in the commodity flight simulation industry, the fidelity that commodity flight simulations can provide, and to provide a high-level overview of the strengths and weaknesses thereof.
2D and 3D low frequency aerodynamics
Authors: Zyl L. H. van
Published: February 2016

Unsteady aerodynamic loads on aircraft configurations are used for aeroelastic or flight dynamic analyses. The sources for deriving these loads include strip theory aerodynamics and three-dimensional panel methods. In some applications the behaviour of the unsteady air loads as the frequency approaches zero is important, and it is well known that the behaviour of strip theory aerodynamics employing the exact circulation function differs qualitatively from that of the three-dimensional panel methods such as the subsonic doublet lattice method (DLM). Theoretical results from an earlier study of the low frequency behaviour of the DLM are used here to show the relationship between the DLM and strip theory and the relationship is verified by a numerical example.
Conceptual design of UAV using Kriging based multi-objective genetic algorithm
Authors: Rajagopal S. , Ganguli R.
Published: February 2016

This paper highlights unmanned aerial vehicle (UAV) conceptual design using the multi-objective genetic algorithm (MOGA). The design problem is formulated as a multidisciplinary design optimisation (MDO) problem by coupling aerodynamic and structural analysis. The UAV considered in this paper is a low speed, long endurance aircraft. The optimisation problem uses endurance maximization and wing weight minimisation as dual objective functions. In this multi-objective optimisation, aspect ratio, wing loading, taper ratio, thickness-to-chord ratio, loiter velocity and loiter altitude are considered as design variables with stall speed, maximum speed and rate of climb as constraints. The MDO system integrates the aircraft design code, RDS and an empirical relation for objective function evaluation. In this study, the optimisation problem is solved in two approaches. In the first approach, the RDS code is directly integrated in the optimisation loop. In the second approach, Kriging model is employed. The second approach is fast and efficient as the meta-model reduces the time of computation. A relatively new multi-objective evolutionary algorithm named NSGA-II (non-dominated sorting genetic algorithm) is used to capture the full Pareto front for the dual objective problem. As a result of optimisation using multi-objective genetic algorithm, several non-dominated solutions indicating number of useful Pareto optimal designs is identified.
Statistical evaluation of flutter boundaries from flight flutter test data
Authors: Abbasi A. A. , Cooper J. E.
Published: February 2016

A methodology is described that determines the statistical confidence bounds on the results from flight flutter tests: modal parameter estimates, flutter margin values and flutter speed estimates, without the need for Monte-Carlo simulation. The approach is based on least squares statistics and eigenvalue perturbation theory applied to the various stages of the analysis process, starting with frequency and damping estimation through to the flutter margin calculations. The technique is demonstrated upon a number of data sets from aeroelastic simulations of flight flutter tests.
Highlights of the Lockheed Martin F-35 STOVL jet effects programme
Authors: Hoggarth R. , Mange Richard
Published: February 2016

This paper presents the highlights of the F-35 STOVL Jet Effects (SJE) test effort during the complete four years of the System Development and Demonstration phase. A new 12%-scale F-35 SJE model was tested in the German-Dutch wind-tunnels Large Low Speed Facility in order to gather STOVL jet-induced Forces and Moments. Ten separate test entries were conducted, covering all STOVL flight regimes from pure hover in ground effect through transition to wing borne flight. This paper will present an overview of this program, including a detailed description of the wind-tunnel model, testing techniques, test conditions, and accomplishments.
A CFD assessment of classifications for hypersonic inlet start/unstart phenomena
Authors: Chang J. , Yu D. , Bao W. , Xie Z. , Fan Y.
Published: February 2016

Inlet start/unstart detection is one of the most important issues of hypersonic inlets and is also the foundation of protection controls of scramjets. In ground and flight tests, it is inevitably to introduce the sensor noises to the measurement system. How to overcome or weaken the influence of the sensor noises and the outer disturbances is an important issue to the control system of the engine. To solve this problem, the 2D inner steady flow of hypersonic inlets was numerically simulated in different freestream conditions and backpressures, and two different inlet unstart phenomena were analysed. The membership function for hypersonic inlet start/unstart can be obtained by using probabilistic output support vector machine, and the algorithm of multiple classifiers fusion is introduced. The variations of the classification accuracy with the intensity of the sensor noises and the number of the classifier were discussed respectively. In conclusion, it is useful to introduce the algorithm of support vector machine and multiple classifiers fusion to overcome or weaken the influence of the sensor noises on the classification accuracy of hypersonic inlet start/unstart. The number of the practical fusion classifiers needs a tradeoff between the fusion classification accuracy and the complexity of the classification system.
Design and implementation of linear-quadratic-Gaussian stability augmentation autopilot for unmanned air vehicle
Authors: Lee C.-S. , Hsiao F.-B. , Jan S.-S.
Published: February 2016

The linear-quadratic-Gaussian (LQG) control synthesis has the advantage of dealing with the uncertain linear systems disturbed by additive white Gaussian noise while having incomplete system state information available for control-loop feedback. This paper hence explores the feasibility of designing and implementing a stability augmentation autopilot for fixed-wing unmanned air vehicles using the LQG approach. The autopilot is composed of two independently designed LQG controllers which control the longitudinal and lateral motions of the aircraft respectively. The corresponding linear models are obtained through a system identification routine which makes use of the combination of two well-established identification methods, namely the subspace method and prediction error method. The two identification methods complement each other well and this paper shows that the proposed system identification scheme is capable of attaining satisfactory state-space models. A complete autopilot design procedure is devised and it is shown that the design process is simple and effective. Resulting longitudinal and lateral controllers are successfully verified in computer simulations and actual flight tests. The flight test results are presented in the paper and they are found to be consistent with the simulation results.
Flutter/LCO suppression for high-aspect ratio wings
Authors: Tang D. , Dowell E. H.
Published: February 2016

An experimental high-aspect ratio wing aeroelastic model with a device to provide a controllable slender body tip mass distribution has been constructed and the model response due to flutter and limit cycle oscillations has been measured in a wind tunnel test. A theoretical model has also been developed and calculations made to correlate with the experimental data. Structural equations of motion based on nonlinear beam theory are combined with the ONERA aerodynamic stall model (an empirical extension of Theodorsen aerodynamic theory that accounts for flow separation). A dynamic perturbation analysis about a nonlinear static equilibrium is used to determine the small perturbation flutter boundary which is compared to the experimentally determined flutter velocity and flutter frequency. Time simulation is used to compute the limit cycle oscillations response when the flutter/LCO control system is ON or OFF. Theory and experiment are in good agreement for predicting the flutter/LCO suppression that can be achieved with the control device.
Unmanned aviation traffic forecast
Authors: Newcome L. R.
Published: February 2016

“Prediction is very difficult, especially if it’s about the future.”

Niels Bohr

The pace at which new technologies are assimilated into society is driven by trends in the regulatory, budgetary, and societal environments in addition to the pace of technology development itself. This study merges trends in these areas to develop an integrated forecast of the levels to which unmanned aviation can be expected to emerge in the military, air cargo, business, general aviation, and airline aviation segments over the coming 40 years. One out of every 80 aircraft on an instrument flight rules (IFR) flight plan over the US are anticipated in this forecast to be unmanned by 2025 and two out of nine (18 of every 80) by 2050. Portions of this study were originally researched in 2005 in support of the Federal Aviation Administration’s (FAA’s) Joint Planning and Development Office (JPDO) for planning the Next Generation (NextGen) air traffic system and later presented at the 23rd Bristol UAV Systems Conference.
Model reduction strategies for nonlinear beams subjected to large rotary actuations
Authors: Stanford B. , Beran P. , Kurdi M.
Published: February 2016

The solution to nonlinear structural dynamics problems with time marching schemes can be very expensive, particularly if the desired time-periodic response takes many cycles to form. Two cost reduction methods, which need not be considered separately, are formulated in this work. The first projects the nonlinear system of equations onto a reduced basis defined by a set of modes computed with proper orthogonal decomposition. The second utilises a monolithic time spectral element method, whereby the system of ordinary differential equations is converted into a single algebraic system of equations. The spectral element method can be formulated such that only the time-periodic response is computed. These techniques are implemented for a planar elastic beam, actuated at its base to emulate a flapping motion. Nonlinear elastic terms are computed with a corotational finite element method, while inertial terms are computed with a standard multibody dynamics formulation. For a variety of actuation frequencies and kinematic motions, results are given in terms of POD modes, reduced order model accuracy, and computational cost, for both the time marching and the monolithic time schemes.
An integrated approach to local ultrasonic monitoring of fastener hole fatigue cracks
Authors: Cobb A. C. , Michaels J. E. , Michaels T. E.
Published: February 2016

Ultrasonic nondestructive evaluation methods are routinely used to detect and size fatigue cracks near fastener holes in aircraft structures as a part of scheduled maintenance. In contrast, statistical crack propagation models provide an estimate of the expected fatigue life assuming a known crack size and future fatigue loadings. Here an integrated approach for in situ diagnosis and prognosis of fastener hole fatigue cracks is proposed and implemented that incorporates both ultrasonic monitoring and crack growth laws. The sensing method is an ultrasonic angle beam technique, and cracks are automatically detected from the ultrasonic response. An extended Kalman filter is applied to combine ultrasonically estimated crack sizes with a crack growth law, effectively using the time history of the ultrasonic results rather than only the most recent measurement. A natural extension of this method is fatigue life prognosis. Results from fatigue tests on 7075-T651 aluminium coupons show improved crack size estimates as compared to those obtained from ultrasonic measurements alone, and also demonstrate the capability of predicting the remaining life. This approach for fatigue crack detection, sizing and prognosis is an example of a general strategy for in situ monitoring of structural damage whereby improved results are achieved from the integration of noisy measurements with imperfect crack growth models.
Goodness dispersion curves for ultrasonic guided wave based SHM: a sample problem in corrosion monitoring
Authors: Gao H. , Rose J. L.
Published: February 2016

Ultrasonic guided wave techniques have great potential for structural health monitoring applications. Appropriate mode and frequency selection is the basis for achieving optimised damage monitoring performance. In this paper, several important guided wave mode attributes are introduced in addition to the commonly used phase velocity and group velocity dispersion curves while using the general corrosion problem as an example. We first derive a simple and generic wave excitability function based on the theory of normal mode expansion and the reciprocity theorem. A sensitivity dispersion curve is formulated based on the group velocity dispersion curve. Both excitability and sensitivity dispersion curves are verified with finite element simulations. Finally, a goodness dispersion curve concept is introduced to evaluate the tradeoffs between multiple mode selection objectives based on the wave velocity, excitability and sensitivity.
Non-linear system identification of the dynamics of aeroelastic instability suppression based on targeted energy transfers
Authors: Lee Y. S. , Vakakis A. F. , McFarland D. M. , Bergman L. A.
Published: February 2016

We revisit our earlier study of targeted energy transfer (TET) mechanisms for aeroelastic instability suppression by employing time-domain nonlinear system identification based on the equivalence between analytical and empirical slow flows. Performing multiscale partitions of the dynamics directly on measured (or simulated) time series without any presumptions regarding the type and strength of the system nonlinearity, we derive nonlinear interaction models (NIMs) as sets of intrinsic modal oscillators (IMOs). The eigenfre-quencies of IMOs are characterised by the ‘fast’ dynamics of the problem and their forcing terms represent slowly-varying nonlinear modal interactions across the different time scales of the dynamics. We demonstrate that NIMs not only provide information on modal energy exchanges under nonlinear resonant interactions, but also directly dictate robustness behaviour of TET mechanisms for suppressing aeroelastic instabilities. Finally, we discuss the usefulness of NIMs in constructing frequency-energy plots that reveal global features of the dynamics to distinguish between different TET mechanisms and to study robustness of aeroelastic instability suppression.
Drag reduction on a spiked body at hypersonic speed
Authors: d’Humières G. , Stollery J. L.
Published: February 2016

Fitting a spike on a blunt body provides a drag reduction at supersonic and hypersonic speeds. In this study, the laminar flow over a spiked, conical body terminated by a spherical cap, inspired by the Apollo re-entry capsule design, was investigated using a hypersonic wind tunnel. Schlieren pictures revealed the absence of flow unsteadiness for the range of spike lengths tested, and force measurements showed a maximum reduction of 77% of the unspiked body drag.

A simple theoretical model based on the pressure drag generated by a solid cone showed good agreement with the experimental data. The measured shock stand-off distance agreed well with predictions.
Starting characteristics of a rectangular supersonic air-intake with cowl deflection
Authors: Das S. , Prasad J. K.
Published: February 2016

Experimental and computational investigations have been made to obtain the details of the flow field of a supersonic air-intake with different cowl deflection angles and back pressures at the exit. The flow field obtained with an inviscid computation on the basic configuration, designed for Mach 2·2, shows starting behaviour whereas computation with k-ω turbulence model and experiments indicate unstart characteristics. Both experiments and computations indicate that provision of a small angle at the cowl tip leads to start of the same intake and also improves it’s performance. Results obtained with cowl deflection shows a better performance in comparison to performance achieved with a basic intake and with a bleed of 2·8%. Sustainable back pressure could be obtained through the computations made at different back pressures for different cowl deflection angles. Overall results suggest that provision of small cowl deflection angle itself leads to improvement in performance achieved in comparison to a bleed of 2·8%, even with back pressure at the exit.
Aerodynamic study of corrugated skins for morphing wing applications
Authors: Thill C. , Downsborough J. D. , Lai S. J. , Bond I. P. , Jones D. P.
Published: February 2016

Corrugated structures offer a potential solution for morphing wing skin applications due to their anisotropic behaviour that allows chordwise camber and length changes. Aerofoils with corrugated skins in the aft 1/3 of the chordwise section have been studied experimentally and computationally using various corrugation shapes and forms (sinusoidal, trapezoidal and triangular) at different Reynolds numbers. The study showed that the aerodynamic performance is highly dependent on corrugation amplitude, wavelength, gradient (combination of amplitude and wavelength) and Reynolds number. Evidence is given highlighting that penalties for having a non-smooth surface in the aft 1/3 of the chordwise section of an aerofoil can be eliminated for the lift curve slope and minimised for the zero lift drag coefficient.
Experimental study of unsteadiness in supersonic shock-wave/turbulent boundary-layer interactions with separation
Authors: Estruch D. , MacManus D. G. , Richardson D. P. , Lawson N. J. , Garry K. P. , Stollery J. L.
Published: February 2016

Shock-wave/turbulent boundary-layer interactions (SWTBLIs) with separation are known to be inherently unsteady but their physical mechanisms are still not totally understood. An experimental investigation has been performed in a supersonic wind tunnel at a freestream flow Mach number of 2·42. The interaction between a shock wave created by a shock generator (α = 3°, α = 9°, α = 13° and α = 15° deflection angles) and a turbulent boundary layer with thickness δ = 5mm has been studied. High-speed Schlieren visualisations have been obtained and used to measure shock wave unsteadiness by means of digital image processing. In the interactions with separation, the reflected shock’s unsteadiness has been in the order of 102Hz. High-speed wall pressure measurements have also been obtained with fast-response micro-transducers along the interactions. Most of the energy of the incoming turbulent boundary layer is broadband and at high frequencies (>104Hz). An addition of low-frequency (<104Hz) fluctuation energy is found at separation. Along the interaction region, the shock impingement results in an amplification of fluctuation energy due to the increase in pressure. Under the main recirculation region core there is only an increase in high frequency energy (>104Hz). Amplification of lower frequency fluctuation energy (>103Hz) is also observed close to the separation and reattachment regions.
NACRE novel aircraft concepts
Authors: Frota J.
Published: February 2016

Commercial transport aircraft developed today are defined to balance all requirements foreseen for the short or medium term. Best engineering knowledge as much as minimum business risks consistently lead to the so-called ‘classic’ aircraft configuration. This balanced approach is efficient but can also inhibit innovative practices.

Ensuring a sustainable growth in the aviation sector may require radical changes in the way we design and operate aircraft. Started in April 2005, NACRE is a four-year European research and technology integrated project, partly funded by the European Community under the Sixth Framework Programme, which aims at integrating and validating technologies that will enable the potential of new aircraft concepts to be assessed.

In order to explore the most relevant capabilities and meet the widest range of challenges, the NACRE R&T project has identified a set of concepts tailored to address specific subsets of design drivers:

• The Pro-Green aircraft concepts putting a major emphasis on the reduction of environmental impact of air travel;

• The Passenger-driven Aircraft concepts aiming at optimised payload and appreciable quality of future aircraft for the end users;

• The Simple Flying Bus, which puts the biggest emphasis on low manufacturing costs and minimum cost of ownership.

Irrespective of what final future product configurations might ever look like, the NACRE aircraft concepts act as basic vectors, encompassing all the expected capability developments. The general project objectives are thus to use these concepts in order to:

• Explore alternative routes for the major aircraft components (fuselage, wing, engine integration) better suited to their specific targets and which would have been rejected in a balanced approach;

• Provide better answers to the full range of requirements by developing and, in some cases, validating the associated envelope of innovative component designs and associated technologies.

NACRE is by essence a focused multidisciplinary approach. It does not concentrate on one specific aircraft concept, but it is aimed at developing solutions at a generic aircraft component level, which will enable the results to be applicable for a range of new aircraft concepts. For each of the major aircraft components, the multidisciplinary investigations will require an exploration of the different associated aspects of aerodynamics, materials, structure, engines and systems with the goal of setting the standards in future aircraft design, thus ensuring improved quality and affordability, whilst meeting the strengthening environmental constraints (emissions and noise), with a vision towards improving significantly the global efficiency of the air transport system.
Effects of boundary-layer bleeding on unstart oscillatory flow of hypersonic inlets
Authors: Fan Y. , Chang J. , Bao W. , Yu D.
Published: February 2016

The unsteady flowfield of a series of mixed-compression hypersonic inlets with different bleeding rates were numerically simulated. Firstly unstart oscillatory flow of hypersonic inlets caused by downstream massflow choking was discussed. Then the effects of boundary layer bleeding on the averaged performance parameter of hypersonic inlets, and on the dominant amplitude and frequency of unstart oscillatory flow of hypersonic inlets were presented. The reasons why the boundary-layer bleeding can suppress unstart oscillatory flow of hypersonic inlets were analysed. In conclusion, the averaged performance parameter of hypersonic inlets during a big buzz is improved greatly, and the dominant frequency of unstart oscillatory flow of hypersonic inlets is reduced in contrast with no bleeding, and all these are benefit to the design and operation of hypersonic inlets.
An overview of experiments on the dynamic sensitivity of MAVs to turbulence
Authors: Watkins A. , Thompson M. , Shortis M. , Segal R. , Abdulrahim M. , Sheridan J.
Published: February 2016

Aspects of the turbulent wind environment Micro Air Vehicles (MAVs) experience when flying outdoors were replicated in a large wind tunnel. An overview of the facility, instrumentation and initial flight tests is given. Piloting inputs and aircraft accelerations were recorded on fixed and rotary wing MAVs and for some tests, measurements of the approach flow (u,v,wsampled at 1,250Hz at four laterally disposed upstream locations) were made. The piloting aim was to hold straight and level flight in the 12m wide × 4m high × ~50m long test section, while flying in a range of turbulent conditions. The Cooper-Harper rating system showed that a rotary craft was less sensitive to the effects of turbulence compared to the fixed wing craft and that while the fixed wing aircraft was relatively easy to fly in smooth air, it became extremely difficult to fly under high turbulence conditions. The rotary craft, while more difficult to fly per. se., did not become significantly harder to fly in relatively high turbulence levels. However the rotary craft had a higher mass and MOI than the fixed wing craft and further work is planned to understand the effects of these differences.
Analysis of turbine performance degradation effects due to geometry variations between actual components and design Intent
Authors: Zachos P. K. , Pilidis P. , Kalfas A. I.
Published: February 2016

This paper presents a computational analysis regarding the effect of the camber line deformation due to structural errors, on the aerodynamic behavior of a high-pressure steam turbine.

In several cases, inaccuracies in the blade geometry can lead to undesirable flow phenomena strongly affecting its overall performance when put in service. The effect of the camber line deformation on the performance of an experimental axial steam turbine is investigated hereafter. A high fidelity inspection of the actual geometry of both a stator and a rotor blades randomly chosen among the similar blades of the same row has been carried out, using a 3D co-ordinate measurement machine. The cross sections of the blades obtained by the measurement were compared with those produced by the design process to evaluate the change in blade inlet/exit angles. The actual (measured) model has been used as input into a streamline curvature solver to evaluate its overall performance assuming a uniform distribution of the geometrical error across the blades of the same blade row, the loss generation mechanisms within the flow field have been further investigated and analysed using a high fidelity 3D Navier-Stokes solver.

A measurable change of efficiency as well as in the total power delivered by the turbine was found. This suggests that the accumulated error caused during the manufacturing procedure plays a significant role in the overall performance of the machine by making it less efficient by almost 1% due to the intensification of the hub and casing secondary flows, as well as to the thicker boundary layers on the blade surfaces revealed by the numerical prediction of the flow.
Aerodynamics – A discipline swept away?
Authors: Rossow C.-C.
Published: February 2016

This contribution is based on the Lanchester Lecture of the Royal Aeronautical Society held in Manchester, UK, in October 2009. The lecture reflected on further possible perspectives for aeronautical research, in particular with respect to aerodynamics. The air transport system of today has matured to very high performance and safety standards. However, due to the ongoing global developments of economy and ecology, new challenges have to be faced. Thus, the relevance of all engineering aeronautical disciplines contributing to the final aircraft configuration is now closely scrutinised, and especially aerodynamics is challenged whether any investment in further research is still justified. In this contribution, it is argued that, when carefully exploited, aerodynamics still offers a substantial technological perspective, well beyond the concepts for the next generation of aircraft as currently being pursued. As an example, the aerodynamics of a forward swept-wing are discussed and it is outlined that, when combining the transonic characteristics of a forward swept-wing with the advantages of natural laminar-flow, considerable improvements in efficiency may be gained. However, this potential may only be leveraged through a strategic, long-term orientation of fundamental and applied research.
Modern developments in hypersonic wind tunnels
Authors: Stalker R. J.
Published: February 2016

The development of new methods of producing hypersonic wind-tunnel flows at increasing velocities during the last few decades is reviewed with attention to airbreathing propulsion, hypervelocity aerodynamics and superorbital aerodynamics. The role of chemical reactions in these flows leads to use of a binary scaling simulation parameter, which can be related to the Reynolds number, and which demands that smaller wind tunnels require higher reservoir pressure levels for simulation of flight phenomena. The use of combustion heated vitiated wind tunnels for propulsive research is discussed, as well as the use of reflected shock tunnels for the same purpose. A flight experiment validating shock-tunnel results is described, and relevant developments in shock tunnel instrumentation are outlined. The use of shock tunnels for hypervelocity testing is reviewed, noting the role of driver gas contamination in determining test time, and presenting examples of air dissociation effects on model flows. Extending the hypervelocity testing range into the superorbital regime with useful test times is seen to be possible by use of expansion tube/tunnels with a free piston driver.
The MIL-STD-1553B data bus: What does the future hold?
Authors: Bracknell D. R.
Published: February 2016

Numerous military platforms (land, sea and air) feature serial data bus technology based on the US MIL-STD-1553B data bus standard for integration of their digital systems. Many of these platforms have 15-20 years of operational life remaining, but the installed 1553B data buses (data networks) having only a 1Mbit/sec transfer rate are unable to meet many of the future data networking requirements. Research into new, higher performance data networks has concentrated on modern alternatives with throughput increases of two to three orders of magnitude (100Mbit/sec to 1Gbit/sec). These are generally based on modern commercial-off-the-shelf (COTS) standards, good examples being Ethernet and Fibre Channel. Some are already being employed in military platforms having been ruggedised for the harsh physical and electro-magnetic environment. However these COTS systems while being a natural choice for new platforms may not be cost effective for upgrading older platforms. This paper plots the history of MIL-STD-1553, possibly the most successful military platform standard of all time, and discusses some of the options for increasing its performance and economically extending its life into the future.
Strategic destruction of the Western commercial aircraft sector: Implications of systems integration and international risk-sharing business models
Authors: Pritchard D. , MacPherson A.
Published: February 2016

This paper offers a critical perspective on the changing organisational structure of the Western commercial aircraft industry. The role of systems integration based on risk-sharing partnerships for new aircraft programmes is explored. We find that build-to-print subcontracting relationships are being replaced by internationally devolved design and engineering tasks for airframe development, signaling a profound change in the geography of commercial aircraft production. While sensible from a financial standpoint, the international outsourcing of design-intensive production entails substantial amounts of technology transfer–including the delivery of proprietary knowledge to risk-sharing partners. For several of the advanced market economies, including Canada, France, Germany, the UK, and the US, the long-range strategic downside is that foreign risk-sharing partners could eventually become competitors. Systems integration on a risk-sharing basis also implies home-country joblosses among skilled workers with expertise in design, engineering, and R&D.
Three-dimensional indicial response of finite aspect ratio yawed wings
Authors: Manglano-Villamarin C. E. , Shaw S. T.
Published: February 2016

The influence of finite aspect ratio and yaw on the computed indicial response of a pitching wing has been studied using numerical solutions of the unsteady Euler equations. The indicial response was obtained directly from computations of the unsteady flow around two- and three-dimensional wings subjected to a step change in incidence at Mach numbers between 0·2 and 0·7. The data reveal several important characteristics in the behaviour of the unsteady response of three-dimensional wings. The initial response is shown to be independent of both aspect ratio and yaw confirming the results of linearized theory. During the subsequent development of the unsteady response significant differences are observed between the two- and three-dimensional behaviours as a consequence of changes to both wing aspect ratio and yaw angle. The formation and spanwise propagation of acoustic waves due to finite aspect ratio is shown to have a significant influence on the development of the unsteady forces, while for yawed wings the results indicate that the manner in which the windward and leeward tip vortices form is important. Based upon these observations it is suggested that the current practice within the rotorcraft community in which two-dimensional indicial response functions are employed may be unreliable for the advancing blade.
Scramjets
Authors: Smart M.
Published: February 2016

The supersonic combustion ramjet, or scramjet, is the engine cycle most suitable for sustained hypersonic flight in the atmosphere. This article describes some of the challenges facing scramjet designers, and the methods currently used for the calculation of scramjet performance. It then reviews the HyShot 2 and Hyper-X flight programs as examples of how sub-scale flights are now being used as important steps towards the development of operational systems. Finally, it describes some recent advances in three-dimensional scramjets with application to hypersonic cruise and multi-stage access-to-space vehicles.