bluuebunny/crossref_metadata_2025_split huggingface dataset:
Aerofoil flow separation suppression using dimples
Authors: Beves C. C. , Barber T. J. 
Published: February 2016

AbstractFlow separation is a source of aerodynamic inefficiency, by using vortex generators flow separation can be controlled. This is of particular benefit to flows around bodies which are susceptible to separated flows, such as bodies in ground effect. Previous studies on the ability of dimples to produce vortices for flow mixing concerned heat transfer applications. Experimental measurements using Laser Doppler Anemometry (LDA) were taken in the wake of the Tyrrell026 aerofoil (Rec = 0·5 × 105) with a dimple array machined in the surface. Results for a dimple array of three rows placed forward of x/c = 0·23 with 1·5D dimple to dimple spacing, showed significant flow recovery in the wake. The velocity deficit of u/Uo,min = −0·1 recovered to u/Uo,min = 0·3 with the dimple array and the size of the wake reduced by 50%; at α = 10°, h/c = 0·313. The positive effect of the dimple array on the wing reduced as the wing was brought closer to the ground.
Vision-based navigation using multi-rate feedback from optic flow and scene reconstruction
Authors: Arvai A. R. , Kehoe J. J. , Lind R. 
Published: February 2016

AbstractVision-based control is being aggressively pursued for autonomous systems. Such control is particularly valuable for path planning to achieve mission objectives like target tracking and obstacle avoidance. This paper presents a multi-rate strategy that utilises a fast-rate optic flow approach and a slow-rate scene reconstruction approach. The vehicle uses scene reconstruction to generate an accurate map for path planning; however, optic flow is used to avoid obstacles while the scene reconstruction is computed. A switch element is used in the feedback path to determine whether information relating to the reconstructed map or the optical flow should be used for navigation. The resulting controller is able to generate flight trajectories and perform obstacle avoidance within a computational cost which is reasonable given performance demands and computational resources on a wide range of aircraft. A simulation demonstrates the performance of an aircraft that uses the multi-rate controller to avoid an obstacle which is only observed after a turn. Essentially, the fast-rate optic flow indicates the presence of the obstacle during the time that slow-rate scene reconstruction is being performed. The resulting flight path is able to follow mission objectives and avoid a collision.
Fidelity enhancement of a rotorcraft simulation model through system identification
Authors: Lu L. , Padfield G. D. , White M. , Perfect P. 
Published: February 2016

AbstractHigh fidelity modelling and simulation are prerequisites for ensuring confidence in decision making during aircraft design and development, including performance and handling qualities, control law developments, aircraft dynamic loads analysis, and the creation of a realistic simulation environment. The techniques of system identification provide a systematic framework for ‘enhancing’ a physics–based simulation model derived from first principles and aircraft design data. In this paper we adopt a frequency domain approach for model enhancement and fidelity improvement of a baseline FLIGHTLAB Bell 412 helicopter model developed at the University of Liverpool. Predictability tests are based on responses to multi–step control inputs. The techniques have been used to generate one, three, and six degree-of-freedom linear models, and their derivatives and predictability are compared to evaluate and augment the fidelity of the FLIGHTLAB model. The enhancement process thus involves augmenting the simulation model based on the identified parameters. The results are reported within the context of the rotorcraft simulation fidelity project, Lifting Standards, involving collaboration with the Flight Research Laboratory (NRC, Ottawa), supported with flight testing on the ASRA research helicopter.
Light gyroplane empennage design considerations
Authors: Houston S. S. 
Published: February 2016

AbstractThe light gyroplane is a class of aircraft popular with amateur constructors and pilots. As a result, there is limited design guidance available since formal technical resources are not available to the community. Rule-of-thumb, intuition and historical experience tend to influence design evolution. Empennage configuration is a prime example of this paradigm, and the objective of this Paper is to explore those factors that influence horizontal stabiliser effectiveness with particular reference to dynamic stability. An individual-blade rotorcraft mathematical model is coupled with a vorticity-based flowfield code, necessary to capture the highly interactional aerodynamics associated with empennage location at the rear of the airframe. A parametric study of horizontal stabiliser location shows that maximum benefit from the energising influence of the propeller slipstream is obtained if the surface is placed near the edge of the propeller wake. Further, traditional design parameters such as tail volume ratio offer an incomplete indicator of empennage effectiveness without consideration of airframe blockage and propeller slipstream. It is concluded that empennage sizing calculations can be straightforward, but require due consideration of the impact of the close-coupled nature of the vehicle on stabilising surface aerodynamic effectiveness.
The tau of flight control
Authors: Padfield G. D. 
Published: February 2016

AbstractWith this survey paper, the author proposes a new ‘tao’ – a new way of understanding – of how pilots do what they do. Research into the control of purposeful action in the natural world suggests that very rapid, efficient and ‘instinctive’ techniques have evolved based on the time to close on a goal, or close a gap, τ(t), and its derivatives. Purposeful actions involve the closure of one or more physical gaps, each with its own time to close, varying with time. Maintaining a constant rate of change of τ(t) with time (< 1) during an approach will ensure a successful arresting when the gap is closed, but an animal’s strategy can be adapted to the circumstances to achieve either a hard stop (aggressive action with ṫ > 0·5), or a soft stop (gentle action with ṫ < 0·5). Synchronous coupling of two motions,x(t) andy(t), such that the times to close are coupled, τx=kτy, results in the motion gapsx(t) andy(t) being related through a power law,x=Cy1/k, and closing smoothly together; examples of such coupling in the form of pursuit tracking in the natural world abound. Research has also shown that gaps can be closed by following ‘intrinsic’ guides, or self-generated mental models of desired motion, that have particular forms; for example, constant deceleration or constant acceleration. The gathering evidence from research into animal behaviour in the natural-world forms a background for the exploration of flight control in the man-made world. The implications for control theory, flight control developments and flight handling qualities, are considered to be profound. τ-theory suggests that natural control has a particular non-linear, albeit very simple, time varying form and that pilots learn control strategy skills by developing mental models, or internalised schemata, in the form of what are described as ‘τ guides’. In this context the author presents his perspective on flight control, briefly reviewing τ-theory and providing examples from research conducted at The University of Liverpool during the period 1999-2011, including the work of several PhD students. Concepts for guidance algorithms suitable for augmented manual or autonomous control are discussed and the implications for handling qualities developments, particularly relating to flight in degraded visual conditions, are presented. Some outstanding questions pointing directions for future research are raised.
Damage tolerant cork based composites for aerospace applications
Authors: Silva J. M. , Nunes C. Z. , Franco N. , Gamboa P. V. 
Published: February 2016

AbstractThis work aims at improving the resilience and damage tolerant properties of CFRP by using cork, which is a natural material with good energy absorption capacity and thermal insulating and vibration damping characteristics. Two types of materials were considered: a sandwich formed by carbon-epoxy facesheets with a cork-epoxy core and a carbon-epoxy laminate with embedded cork granulates. The damage tolerant properties were evaluated by low velocity impact tests according to the type of material. Additionally, this work intends to evaluate the feasibility of using a cork agglomerate combined with CFRP in a sandwich configuration in order to improve the aeroelastic properties of certain types of aerospace components aiming at preventing the occurrence of damage due to flutter. A computational analysis was used to determine the critical flutter speed of a cork based sandwich plate and other conventional materials, such as aluminium alloy and CFRP.Results are clear about the benefits of using cork based composites either by improving the damage tolerant properties under impact loading or by extending the flight envelope without weight penalty by increasing the flutter critical speed.
Dimensional modelling of the fuel outgassing phenomenon: Improving flammability assessment of aircraft fuel tanks
Authors: Harris A. P. , Ratcliffe N. M. 
Published: February 2016

AbstractFuel outgassing (oxygen evolution) within aircraft fuel tanks presents a serious flammability hazard. Time constants representing oxygen transfer rate, from the fuel into a tank’s ullage, are used to model the effect of outgassing on tank flammability. These time constants are specific to a single aircraft type and flight envelope and may not accurately represent fuel outgassing behaviour for other aircraft types with differing fuel tank configurations and flight envelopes. To improve current modelling practice for more accurate flammability analysis dimensional modelling has been used to determine the rate of oxygen evolution from Jet A-1 fuel in an aircraft fuel tank. Measurements of oxygen evolution rate, made on a dimensionally similar model, have been projected to an A320 aircraft. The evolution of oxygen from the fuel was found to increase monotonically with time. Fitting the test data with an inverse-exponential function enabled oxygen release rate and its associated time constant (τ) to be determined. Dimensional modelling of aviation fuel outgassing using model fuel tanks will enable oxygen evolution rate from aviation fuel to be determined for a wide range of aircraft fuel tank configurations and environments without the need for flight testing. In turn the accuracy of flammability assessment of aircraft fuel tanks will be improved and significant cost savings made.
Challenges to overcome for routine usage of automatic optimisation in the propulsion industry
Authors: Shahpar S. 
Published: February 2016

AbstractIn industry, there is an ever-increasing requirement not only to design high performance new products but also to deliver them at lower cost and in shorter time. To meet these demanding engineering challenges, it is not sufficient to treat the different disciplines involved in a product design in isolation; rather they must be considered together as an integrated system that reflects the dependencies and interactions of the different disciplines. The design process must be automated to meet the stringent design time-lines. In spite of promising forays for over a decade, automatic design optimisation (ADO) and multidisciplinary optimisation (MDO) has not been widely adapted by the Turbomachinery design practitioners. This presentation will explore some of the technical and nontechnical barriers such as cultural and organisational issues that must be addressed if ADO/MDO is to be used routinely in industry. Some recent, successful application of automatic optimisation is also reported herein.
Survey of aircraft structural dynamics non-linear problems and some recent solutions
Authors: Pérez J. L. , Benítez L. H. , Oliver M. , Climent H. 
Published: February 2016

AbstractStructural dynamics is a key discipline in aircraft design and certification. The realm of structural dynamics includes problems in which structure flexibility is important, such as dynamic loads (landing, taxi, gust, turbulence...), but it also includes other areas like environmental vibration or impacts technology. This is closely related with its sister discipline Aeroelasticity.Linearity has been the cornerstone assumption in aircraft design engineering solutions. In the past, linearity allowed to solve many structural dynamics problems that otherwise would have been unaffordable. Nowadays, the necessity of highly optimised structures, combined to an increase of computer power, has made this assumption to be reconsidered.This paper presents a wide survey on non-linear topics in structural dynamics and the way they have been solved at EADS-CASA (Airbus military) in the past 25 years. Although the paper has been mainly focused on numerical simulation using the Finite Element Method technique, component tests and full aircraft tests are also presented.
A feasibility assessment of annular winged VTOL flight vehicles
Authors: Saeed B. , Gratton G. , Mares C. 
Published: February 2016

AbstractThis paper presents a feasibility study to integrate a developed lift system (an annular wing wrapped around a centrifugal flow generator) into a Vertical/Short Take-Off and Landing V/STOL aircraft. Different physical scales, from micro aerial vehicle to a Harrier Jump Jet scale, for a variety of propulsion systems are explored. The system has shown to be viable for several classes of aircraft but with better performance offered by a micro-aerial-vehicle (~40g) and a large vehicle (~10,000kg) with a turbofan engine, albeit in both cases with apparently worse performance than is offered by current technologies. The wingform does not appear to be feasible in the light aircraft scale whilst using internal combustion engines.
Span-wise wind fluctuations in open terrain as applicable to small flying craft
Authors: Thompson M. , Watkins S. , White C. , Holmes J. 
Published: February 2016

AbstractMicro air vehicles (MAVs) are typically of low mass and moment of inertia and have flight speeds comparable to birds and the larger insects. Such craft traverse the lower levels of the atmospheric boundary layer (ABL) which is a significantly different environment than that experienced by larger manned aircraft, which spend the majority of their time in relatively clean air and fly at speeds significantly higher than typical wind speeds in the ABL. Here a new series of measurements dedicated to understanding spatial and temporal velocity fields that MAVs experience are presented. Atmospheric wind measurements were taken by sampling four multi-hole dynamic pressure probes spanned perpendicular to the oncoming wind at spans of between 0·014m and up to 0·45m. It was noted that the variation of both longitudinal velocity and flow pitch angle against spacing followed a fractional power law and as such large variations were present even for the smallest inter-probe separations. This effect is thought to explain the increasing piloting difficulties experienced in maintaining good roll control for decreasing scales of craft.
Composite materials, composite structures, composite systems
Authors: van Tooren M. , Kasapoglou C. , Bersee H. 
Published: February 2016

AbstractThe first part of the history of composites in aerospace emphasised materials with high specific strength and stiffness. This was followed by a quest for reliable manufacturing techniques that guaranteed sufficiently high fibre volume fractions in complex structural parts with reasonable cost. Further improvements are still possible leading, ultimately to an extension of the functionality of composite structures to non-mechanical functions. Reduction of material scatter and a more probability-based design approach, improved material properties, higher post buckling factors, improved crashworthiness concepts and improved NDI techniques are some of the evolutionary measures that could improve the performance of current composite structures. Modular design, increased co-curing, hybrid material structures, hybrid fabrication methods, innovative structural concepts and reduced development times are more revolutionary steps that could bring today’s solutions further. Manufacturing engineering is also important for achieving revolutionary change. Function integration such as embedded deicing, morphing,, and boundary-layer suction are among the next steps in weight and cost reduction, but now on the system level.
A further case for variable geometry
Authors: Johl W. A. T. ‘Fritz’ 
Published: February 2016

AbstractToday, all sailplanes in any particular class look and perform more or less the same. This gives credence to the view that the necessary compromises in design and sailplane technology have reached a limit. Sailplane development is on a sort of plateau. Further, apart from perhaps boundary-layer control (BLC), there appears to be nothing in the foreseeable future that promises any significant improvement in performance. It is the purpose of this paper to, once again, encourage interest in Variable Geometry (VG) and address the controversies which prevailed in abundance during the 1970s and which apparently still survive today.
High-accuracy four-dimensional trajectory prediction for civil aircraft
Authors: Schuster W. , Porretta M. , Ochieng W. 
Published: February 2016

AbstractCurrent state-of-the-art trajectory prediction tools typically model aircraft as three-dimensional point-masses, and make a number of simplifying assumptions about the actual and anticipated dynamics states of the aircraft. They are typically based on predefined settings obtained from existing databases such as Eurocontrol’s Bada rather than real-time information, including on the environment, available onboard the aircraft. This significantly limits trajectory prediction performance. This paper proposes a high-accuracy four-dimensional trajectory prediction model for use onboard civil aircraft, as well as by ground-based systems, which addresses these limitations. It is designed for strategic traffic capacity optimisation and conflict-detection and resolution over time-horizons covering the entire duration of a flight. The model incorporates a number of features including a novel flight-control-system and an enhanced flight-script that incorporates new taxonomy and content thereby enabling better definition of aircraft intent. The accuracy of the model is characterised using operational data acquired during a real flight trial. Results show that the performance of the proposed model is significantly better than the current models. Its accuracy is better than the required navigation performance for departure, en route and Non-Precision-Approach phases of flight.
Computational investigation of cavity flow control using a passive device
Authors: Khanal B. , Knowles K. , Saddington A. J. 
Published: February 2016

AbstractIn this paper, flow control effectiveness of a passive device in relation to open cavity flowfield is investigated computationally and compared with experimental work. Specifically the modification in the cavity flowfield due to the presence of a spoiler is studied in details to explain the physics behind the flow control effects. A combination of 2D and 3D flow visualisation tools are used to understand the flow behaviour inside the cavity and the quantitative analysis of the unsteady pressure fluctuations is also performed to assess the unsteady effects. Flow simulations with a turbulence model based on a hybrid RANS/LES (commonly known as Detached-Eddy Simulation (DES)) are used in this study. The time-mean flow visualisation clearly showed the presence of three dimensional effects inside the empty cavity whereas the 3D effects were found to diminish in the presence of a spoiler. In the unsteady flow analysis, near-field acoustic spectra were computed for empty cavity as well as cavity-with-spoiler cases. Study of unsteady pressure spectra for the cavity-with-spoiler case was found to record the complete suppression of the dominant tones in the presence of the spoiler. The analysis has indicated that the main reason behind this suppression is due to the inability of faintly energised vortical structures (faintly energised as a result of the extraction of turbulent kinetic energy by the spoiler) to maintain the unsteady flapping of the separated shear layer.
6U CubeSat commercial applications
Authors: Tsitas S. R. , Kingston J. 
Published: February 2016

AbstractRecent work by Tsitas and Kingston(1) has demonstrated that an 8kg 6U CubeSat can be designed to perform Earth observation missions equivalent to those of 50-150kg microsatellites. Their design is reviewed and its commercial potential is compared to the 156kg RapidEye spacecraft. Three other commercial applications of this design are described. These are: a standard spacecraft for space scientists and astronomers; the spacecraft component of an N nation 5 spectral band disaster monitoring constellation and a night imaging satellite. Nanosatellites should now be considered for commercial missions previously thought to require microsatellites.
Influence of stores on the flow inside UCAV weapon bays
Authors: Lawson S. J. , Barakos G. N. 
Published: February 2016

AbstractDetached-eddy simulations for the 1303 UCAV geometry are undertaken aiming to investigate the flow physics of the interaction of a store with the flow inside a UCAV weapons bay. Advanced multi-block topologies had to be used to properly represent the planform of the UCAV and all the details of the weapon bay, including doors and hinges, while sliding meshes were needed to insert the store into the UCAV configuration. Results with an empty bay were encouraging for such complex configurations. Flow visualisation revealed the added turbulent content due to the door leading edges and hinges. The addition of a store in between the doors had little effect close to the front wall of the bay. However averaged flow-fields showed that the proximity of the shear layer to the apex of the store deflected it downwards into the bay and restricted its growth.
Flow distortion in an S-duct inlet with simulated icing effect and heat transfer
Authors: Jin W. , Taghav R. R. , Farokhi S. 
Published: February 2016

AbstractA diffusing S-duct aircraft intake system is computationally studied for the effects of inlet icing and wall heat transfer on engine face distortion. A Reynolds-Averaged Navier-Stokes (RANS) code with k -ω SST turbulence model is used to simulate the compressible viscous flow in the duct. The glaze ice accretion on the inlet lip is simulated as a fixed protrusion from NASA LEWICE3D code. The shape and size of the ice on the inlet lip are assumed to remain constant even in the case of the heated wall. The case of zero external heat transfer is modeled by the adiabatic wall boundary condition, and constant-wall temperature is used to simulate the heated wall effect. The freestream Mach number of 0·85 and glaze ice condition on the inlet lip produce massive flow separation at the lip and internal shock cell structure in the S-duct. The heated wall creates additional vorticity and thus increases the engine face distortion level. The area-averaged total pressure distortion at the engine face in a freestream Mach number of 0·85 is increased by ~7% in the heated wall case as compared to the adiabatic flow.