bluuebunny/crossref_metadata_2025_split huggingface dataset:
Application of synthetic jet actuators for the modification of the characteristics of separated shear layers on slender wings
Authors: Watson M. , Jaworski A. J. , Wood N. J. 
Published: February 2016

AbstractThis paper presents an experimental investigation related to controlling the unsteady characteristics of the separated shear layers occurring over highly swept wings, and in particular focuses on application of synthetic jet actuators for modification of unsteady dynamic loading on the wing surface due to the phenomenon referred to as vortex breakdown (vortex burst).In the post burst flow region the surface pressure measurements reveal the presence of certain characteristic spectral peaks that are thought to represent the presence of a spiralling filament of vorticity inside the expanded vortex that is known to be present in the burst flow over swept wings.This paper details an investigation into how the use of an array of 18 discrete synthetic jet actuators, distributed along the leading edge of a delta wing with a 60° sweep angle, can be used to alter the spectral content of this unsteadiness and reduce the level of unsteady pressure found in the post-burst region toward the wing trailing edge by up to 40%.Measurements of the surface pressure spectral distributions over the wing are presented together with PIV measurements of the vortex cross-section, conducted in the successive planes parallel to the wing trailing edge. Additional surface flow visualisation indicates that the effect of the actuators on the leading edge boundary layer is to induce local separation delays close to each actuator orifice, which introduce ‘ripples’ into the shear layer as it separates. The results obtained are used to formulate an interpretative hypothesis attempting to explain the mechanisms responsible for modification of the spectral content and the level of excitation measured on the wing surface.
Modelling the interaction of helicopter main rotor and tail rotor wakes
Authors: Fletcher T. M. , Brown R. E. 
Published: February 2016

AbstractThe mutual interaction between the main rotor and tail rotor wakes is central to some of the most problematic dynamic phenomena experienced by helicopters. Yet achieving the ability to model the growth and propagation of helicopter rotor wakes with sufficient realism to capture the details of this interaction has been a significant challenge to rotorcraft aerodynamicists for many decades. A novel computational fluid dynamics code tailored specifically for rotorcraft applications, the vorticity transport model, has been used to simulate the interaction of the rotors of a helicopter with a single main rotor and tail rotor in both hover and low-speed quartering flight, and with the tail rotor rotating both top-forward and top-aft. The simulations indicate a significant level of unsteadiness in the performance of both main and tail rotors, especially in quartering flight, and a sensitivity to the direction of rotation of the tail rotor. Although the model thus captures behaviour that is similar to that observed in practice, the challenge still remains to integrate the information from high fidelity simulations such as these into routine calculations of the flight dynamics of helicopters.
Remarks on the nonlinear dynamics of a typical aerofoil section in dynamic stall
Authors: Galvanetto U. , Peirò J. , Chantharasenawong C. 
Published: February 2016

AbstractWe use standard tools of the theory of dynamical systems such as phase plots, bifurcation diagrams and basins of attraction to analyse and understand the dynamic behaviour of a typical aerofoil section under dynamic stall conditions. The structural model is linear and the aerodynamic loading is represented by the Leishman-Beddoes semi-empirical dynamic stall model. The loads given by this model are nonlinear and non-smooth, therefore we have integrated the equation of motion using a Runge-Kutta-Fehlberg (RKF45) algorithm equipped with event detection. We perform simulations of the motion for a range of Mach numbers and show that the model is very sensitive to small variations. This is evidenced by the presence in the bifurcation diagram of co-existing attractors or, in other words, by the existence of more than one steady-state motion for a given Mach number. The mechanisms for the appearance and disappearance of the co-existing attractors are elucidated by analysing the evolution of their basins of attraction as the Mach number changes.
Spacecraft control with constrained fast reorientation and accurate pointing
Authors: Mengali G. , Quarta A. A. 
Published: February 2016

AbstractIn this paper we study large angle rotational manoeuvres of spacecraft. The problem of attitude control is formulated and solved through potential functions, thus simplifying frequent reorientation manoeuvres. A combination of gas jet and FEEP thrusters is employed in order to obtain short settling times while meeting stringent pointing requirements. In this way, spacecraft reorientation is achieved in two integrated steps by means of a discrete/continuous control law. Autonomous avoidance of undesired space orientations is obtained and constraints due to the solar array pointing requirements are satisfied. A case study is discussed where the methodology is applied to a large space telescope.
Experimental investigation on wall pressure distribution in flaps’ separating regions
Authors: Zhang P. F. , Wang J. J. , Li Y. C. 
Published: February 2016

AbstractThe effects on the wall pressure of the plate caused by the introduction of a gap near the ground and the flaps were investigated experimentally. The mean pressure on the plate surface was found to decrease with the size changing of the gap near the ground when the gap size (g) is larger than the flap height (h), but the one in the recirculation region increase with the size of the gap when the gap size is about 0 ≤ g ≤ 2h. Three kinds of flow structure appear with increasing the gap sizes, and the transit point is at g/h = 0·2, 0·8 respectively. For the zigzag flap (d/h = 0·19, d is the height of the zigzag), the variation of wall pressure with g/h is similar to the flat flap in general. The zigzag affects the mean wall pressure in the region of 0 ≤ x/h ≤ 20 (the recirculation zone) and can decrease the fluctuating pressure in the region of x/h > 20 downstream.
A wind-tunnel based study of helicopter tail rotor blade vortex interaction
Authors: Coton F. N. , Galbraith R. A. McD. , Wang T. , Newman S. J. 
Published: February 2016

AbstractThe interaction of a helicopter tail rotor blade with the tip vortex system from the main rotor is a significant source of noise and, in some flight states, can produce marked reductions in control effectiveness. This paper describes a series of wind-tunnel tests to simulate tail rotor blade vortex interaction with a view to providing data for the development and validation of numerical simulations of the phenomenon. In the experiments, which were carried out in the Argyll wind-tunnel of Glasgow University, a single-bladed rotor located in the tunnel’s contraction was used to generate the tip vortex which travelled downstream into the working section where it interacted with a model tail rotor. The tail rotor was instrumented with miniature pressure transducers that measured the aerodynamic response during the interaction. The results suggest that the rotor blade vortex interaction is similar in form to that measured at much higher spatial resolution on a fixed, non-rotating blade. The combination of the two datasets, therefore, provides a valuable resource for the development and validation of predictive schemes.
Multigrid multiblock hovering rotor solutions
Authors: Allen C. B. 
Published: February 2016

AbstractThe effect of multigrid acceleration implemented within an upwind-biased Euler method for hovering rotor flows is presented. Previous work has considered multigrid convergence for structured single block rotor solutions. However, for forward flight simulation a multiblock approach is essential and, hence, the flow-solver has been extended to include multigrid acceleration within a multiblock solver. 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. 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 here to be less effective for hovering rotor flows. Previous single block simulations demonstrated that a simple multigrid V-cycle was the most effective, smoothing in the decreasing mesh density direction only, with a relaxed trilinear prolongation operator. This is also shown to be the case for multiblock simulations. Results are presented for multigrid computations with 2, 3, and 4, mesh levels, and a CPU reduction of approximately 80% is demonstrated for 4 mesh levels.
Limited life engines for UAVs
Authors: Clark I. K. 
Published: February 2016

AbstractThe ever expanding range of applications for unmanned air vehicles covers a wide variety of powerplant requirements. While many vehicles are high value assets and demand similar powerplant attributes to a conventional manned aircraft, there is an emerging requirement for powerplants which are designed to a limited life philosophy. This covers a range of applications: at the simplest level there are vehicles where the mission definition dictates that attrition rates will be high, for example low level reconnaissance, targeting or battle damage assessment, and the entire vehicle may only be expected to make a short number of missions. On the other hand there are applications where it may be more cost effective to remove the need for engine maintenance and to treat the powerplant as a disposable limited life unit.In general, the industry trend is towards the reduction of life cycle costs, and a significant emphasis is placed upon continuing to increase aero-engine component lives though novel design and improved manufacturing techniques. A limited life application calls for a different approach, as it may be that the powerplant has a life requirement of anywhere between 50 and 250 hours. This allows scope to explore areas of design and manufacture which would not be suitable for a ‘conventional’ engine and can lead to large reductions in engine cost.This paper seeks to identify the primary cost drivers for a small UAV powerplant in the 10kN thrust class, and to establish the relationships between cost, life and performance at both a whole engine and an individual component level. It also explores the feasibility of using new or unconventional designs and manufacturing methods, and presents a selection of examples.
Joint fixity effect on structural design of a box wing aircraft
Authors: Jemitola P. O. , Fielding J. , Stocking P. 
Published: February 2016

AbstractA computational study was performed to compare the stress distributions in finite element torsion box models of a box wing structure that result from employing four different wing/end fin joint fixities. All considered wings were trimmed in pitch. The joint fixities refer to the type of attachment that connects the tip of the fore and aft wings to the end fin. Using loads from a vortex lattice tool, the analysis determined the best wing-joint fixity of a statically loaded idealised box wing configuration by comparing the stress distributions resulting from the different wing joints in addition to other essential aerodynamic requirements. Analysis of the wing joint fixity indicates that the rigid joint is the most suitable.
Conceptual design and sizing of airframe panels according to safe-life acoustic fatigue criteria
Authors: Ajaj R. M. , Allegri G. , Isikveren A. T. 
Published: February 2016

AbstractThis paper presents a methodology that permits accounting for acoustic fatigue effects when sizing safe-life structural skin-stringer panels at the conceptual design stage of aircraft product development. The approach is based upon estimation of the maximum noise radiated from an entry-into-service year 2020 turbofan. Sonic fatigue endurance is assessed for different skin-stringer panels having different values of skin thickness, rib pitch and stringer pitch. Three different materials were considered in this study: aluminium 2024-T3 alloys (Al 2024-T3); carbon fibre-reinforced plastics (CFRP); and, glass reinforced fibre metal laminate (Hybrid Glare-3). The study resulted in CFRP having the most favourable sonic fatigue performance. In order to link economic considerations into technical decision making, the sonic endurance methods were coupled with an industry grade costing analysis tool (SEER-HTM) to examine the impact of safe-life design on the panel cost and weight. The presented methodology has been shown to be sufficiently generic in nature and robust. This will not only assist in identifying acoustic fatigue as a potential critical design scenario, but will also increase throughput during conceptual design sizing and optimisation.
A comprehensive rotary-wing data base for code validation: the HART II international workshop
Authors: van der wall B. G. 
Published: February 2016

Abstract
The HART II test of 2001 provided a significant and comprehensive database of rotor loads, blade motion, blade pressure distribution, acoustic signature and flow field data. A sub-set of these were released for public access worldwide and an International HART II Workshop was established in 2005. This Workshop, open to the international rotorcraft community, has been held since then at both the AHS Annual Forum as well as the European Rotorcraft Forum. Following the requests of participants, the HART II International Workshop database has been undergoing continuous development. This paper describes the current content and status of the data and the documentation material provided within the workshop database.
A framework for optimising aspects of rotor blades
Authors: Johnson C. S. , Barakos G. N. 
Published: February 2016

AbstractThis work presents a computational framework for the optimisation of various aspects of rotor blades. The proposed method employs CFD combined with artificial neural networks, employed as metamodels, and optimisation methods based on genetic algorithms. To demonstrate this approach, two examples have been used, one is the optimal selection of 4- and 5-digit NACA aerofoils for rotor sections and the other is the optimisation of linear blade twist for rotors in hover. For each case, an objective function was created and the meta-model was subsequently used to evaluate this objective function during the optimisation process. The obtained results agree with real world design examples and theoretical predictions. For the selected cases, the artificial neural network was found to perform adequately though the results required a substantial amount of data for training. The genetic algorithm was found to be very effective in identifying a set of near-optimal parameters. The main CPU cost was associated with the population of the database necessary for the meta-models and this task required CFD computations based on the Reynolds-averaged Navier-Stokes equations. The framework is general enough to allow for several design or optimisation tasks to be carried out and it is based on open-source code made available by the authors.
Robust scheduled control of longitudinal flight with handling quality satisfaction
Authors: Saussié D. , Bérard C. , Akhrif O. , Saydy L. 
Published: February 2016

AbstractClassic flight control systems are still widely used in the industry because of acquired experience and good understanding of their structure. Nevertheless, with more stringent constraints, it becomes difficult to easily fulfil all the criteria with these classic control laws. On the other hand, modern methods can handle many constraints but fail to produce low order controllers. The following methodology proposed in this paper addresses both classic and modern flight control issues, to offer a solution that leverages the strengths of both approaches. First, an H∞ synthesis is performed in order to get controllers which satisfy handling qualities and are robust with respect to mass and centre of gravity variations. These controllers are then reduced and structured by using robust modal control techniques. In conclusion, a self-scheduling technique is described that will schedule these controllers over the entire flight envelope.
Modelling of static aerodynamics of helicopter underslung loads
Authors: Greenwell D. I. 
Published: February 2016

AbstractThe complex aerodynamics of rectangular underslung helicopter loads can lead to severe stability problems, but are difficult to represent in flight dynamics models. Current models for box aerodynamics are highly unsatisfactory, being entirely empirical and requiring large amounts of experimental data to generate. This paper presents a new modelling approach, which takes account of the bluff-body nature of the flow, where loads are dominated by normal pressure forces. Existing experimental data is recast in body-axes form, with α and β replaced by velocity components perpendicular and parallel to the box faces. Force and moment data for a wide range of boxes then collapse onto a set of simple generic characteristics, with features that can be related directly to the underlying flow physics. Modelling of container aerodynamics is greatly simplified, and allowance for effects of turbulence, Reynolds Number, wind tunnel interference and geometry modifications becomes possible.
A first order method for the determination of the leading mass characteristics of civil transport aircraft
Authors: Poll D. I. A. 
Published: February 2016

AbstractSimple, approximate relations are developed that allow rapid, yet accurate, estimates of the principal mass characteristics of modern civil transport aircraft. The method is based upon an ‘aircraft mass hypothesis’ combined with data taken from Type Certificates and manufacturers’ information for 44 different Boeing and Airbus aircraft types and variants. This hypothesis links the masses of the various aircraft components, including the operational items, and the maximum payload mass to just two parameters; the passenger cabin floor area, as exemplified by the ‘design passenger number’ and the ratio of maximum zero fuel mass to maximum take-off mass, as exemplified by the non-dimensional ‘design range’. In this context, the ‘design range’ is defined as the maximum possible range when the aircraft is operating at its maximum zero fuel mass. This approach leads to the formulation of three basic ‘laws’ for aircraft mass. Special consideration is given to the identification and separation of those components that are fixed either by the design, or the certification process, and those that are free, within defined limits, to be chosen by the operator.
An operability framework for unmanned aircraft systems
Authors: Maneschijn A. , Jones T. , von Backström T. W. 
Published: February 2016

AbstractIn the current absence of comprehensive and generic UAS airworthiness regulations, the development of UAS and their introduction into non-segregated airspace pose significant challenges to the UAS industry and regulators. This paper reports on a research study that considered the problem, from an engineering perspective, beyond the limits of the airworthiness of the aircraft and remote control station. The study introduces the concept of UAS operability, which includes the safe and reliable functioning of the UAS as a system, the airworthiness of its airborne sub-systems, and the safe and reliable functioning of its non-airborne sub-systems and functional payloads. The regulatory domain for UAS operability is described and the study establishes a generic and comprehensive UAS operability framework. The framework was validated by populating its elements with engineering criteria that can be used by the UAS engineering domain for the development of engineering specifications and as guidance towards achieving the safe and reliable functioning of UAS.
Numerical investigation of aeroheating characteristics of spiked blunt bodies at Mach six flight conditions
Authors: Ahmed M. Y. M. , Qin N. 
Published: February 2016

AbstractAdding a small aerodisk at the tip of the spike was proved to improve the spike’s performance in reducing the drag. If designed properly, the aerodisk spike can offer better performance in drag reduction in comparison with the pointed sharp-nosed spike. However, the impact of the aerodisk on the aeroheating reduction capabilities of the spike was not investigated in detail before. In the present work, a numerical investigation of the aerothermodynamic characteristics of spiked blunt bodies at Mach 6 flight conditions is conducted. It was found that, adding an aerodisk degrades the performance of the spike in reducing the aeroheating level. Nonetheless, the latter remains below that of the unspiked body.
Applying heat pipes to a novel concept aero engine: Part 2 – Design of a heat-pipe heat exchanger for an intercooled-recuperated aero engine
Authors: Camilleri R. , Ogaji S. , Pilidis P. 
Published: February 2016

AbstractWith the ever-increasing pressure for cleaner and more fuel efficient aero engines, gas turbine manufacturers are faced with a big challenge which they are bound to accept and act upon. The path from current high bypass ratio (BPR) engines to ultra high BPR engines via geared turbo fans will enable a significant reduction in SFC and CO2 emissions. However, in order to reach the emission levels set by the advisory council for aeronautics research in Europe (ACARE), the introduction of more complex cycles that can operate at higher thermal efficiencies is required. Studies have shown that one possibility of achieving higher core efficiencies and hence lower SFC is through the use of an intercooled recuperated (ICR) core. The concept engine, expected to enter into service around 2020, will make use of a conventional fin plate heat exchangers (HEX) for the intercooler and a tube type HEX as the recuperator. Although the introduction of these two components promises a significant reduction in SFC levels, they will give also rise to higher engine complexity, pressure losses and additional weight. Thus, the performance of the engine relies not only on the behaviour of the usual gas turbine components, but will be heavily dependent on the two heat exchangers. This paper seeks to introduce a heat pipe heat exchanger (HPHEX) as alternative designs for the intercooler and the recuperator. The proposed HPHEX designs for application in an ICR aero engine take advantage of the convenience of the geometry of miniature heat pipes to provide a reduction in pressure losses and weight when compared to conventional HEX. The proposed HPHEX intercooler design eliminates any ducting to and from the intercooler, offering up to 32% reduction in hot pressure losses, 34% reduction in cold pressure losses and over 41% reduction in intercooler weight. On the other hand the proposed HPHEX recuperator design can offer 6% improvement in performance, while offering 36% reduction in cold pressure losses, up to 80% reduction in hot pressure losses and over 31% reduction in weight. An ICR using HPHEX for the intercooler and recueprator may offer up to 2·5% increase in net thrust, while still offering 3% reduction in SFC and up to 7·7% reduction in NOX severity parameter, when compared to the ICR using conventional HEX.