bluuebunny/crossref_metadata_2025_split huggingface dataset:
Impacts of aero-engine deteriorations on military aircraft mission's effectiveness
Authors: Naeem M. , Singh R. , Probert D. 
Published: July 2016

Abstract
International political and socio-economic developments have led the armed forces of many countries to become more aware of how their increasingly-stringent financial budgets are spent. One major expenditure for military authorities is upon aero-engines, because in-service deterioration in any mechanical device, such as an aircraft's gas-turbine engine, is inevitable. Each deterioration has an adverse effect on the performance and shortens the reliable operational life of the engine, thereby resulting in higher life-cycle costs. For a military aircraft's mission-profiles, the consequences of an aero-engine's deterioration upon the aircraft's operational-effectiveness as well as its fuel consumption and life have been predicted in this project using validated computer-simulations. These help in making wiser management-decisions, so leading to the achievement of improved engine utilisation, lower overall life-cycle costs and optimal mission effectiveness for squadrons of aircraft.
Multigrid upwind Euler/Navier-Stokes computation on adaptive unstructured meshes
Authors: Zheng Y. , He L. 
Published: July 2016

AbstractAn unstructured flow solver with adaptive mesh refinement and multigrid acceleration is developed to efficiently compute two-dimensional inviscid and viscous steady flows about complex configurations. High resolution is achieved by using the upwind scheme coupled with adaptive mesh refinement. An aspect-ratio adaptive multigrid method is developed and applied to effectively accelerate the solution convergence of the explicit time-marching in the near wall regions with high aspect mesh ratios. Numerical examples are presented for configurations and conditions ranging from transonic to low speed flows to demonstrate accuracy, speed, and robustness of the method.
Embedded direct numerical simulation for aeronautical CFD
Authors: Sandham N. D. , Alam M. , Morin S. 
Published: July 2016

AbstractA method is proposed by which a direct numerical simulation of the compressible Navier-Stokes equations may be embedded within a more general aeronautical CFD code. The method may be applied to any code which solves the Euler equations or the Favre-averaged Navier-Stokes equations. A formal decomposition of the flowfield is used to derive modified equations for use with direct numerical simulation solvers. Some preliminary applications for model flows with transitional separation bubbles are given.
A data exchange method for fluid-structure interaction problems
Authors: Goura G. S. L. , Badcock K. J. , Woodgate M. A. , Richards B. E. 
Published: July 2016

AbstractThis paper presents and illustrates an interpolation method for the exchange of displacement data between fluid and structural meshes in a fluid-structure interaction simulation. The method is a local method where element volume conservation is central, and does not rely on information from the structural model. Results are evaluated for several two and three dimensional problems. Comparisons with the infinite plate spline method show that the new method gives a more realistic representation of the recovered surface than currently used methods.
A dual-time method for the solution of the
unsteady Euler equations
Authors: Gaitonde A. L. 
Published: July 2016

AbstractA “dual-time” method for solving the three-dimensional Euler equations describing the compressible flow about wings undergoing arbitrary motions and deformations is presented. A finite-volume formulation is chosen where the volumes distort as the wing moves or deforms. Independent motion of the inner and outer boundaries of the grid is permitted with a sequence of grids generated using transfinite interpolation.An implicit real-time discretisation is used, and the equations are integrated in a fictitious pseudo time. This approach allows the real-time step to be chosen on the basis of accuracy rather than stability. It also permits the acceleration techniques commonly used to speed up steady flow calculations to be used when marching in pseudo time, without compromising real-time accuracy. A two-dimensional version of the method has also been developed and results for both two and three-dimensional transonic flows are presented and compared with experimental data where available.
Phenomena observed during aerofoil ramp-down motions from the fully separated state
Authors: Green R. B. , Galbraith R. A. McD. 
Published: July 2016

AbstractUnsteady pressure data from seven aerofoil models performing constant pitch rate “ramp-down” motions from the fully separated state to low incidence have been analysed. It is observed that the time delay between attachment at the leading edge and the occurrence of minimum normal force is, to a first order, independent of reduced pitch rate. As a result, at sufficiently high pitch rate, negative normal force may be generated at large positive incidence. In contrast to this, the re-establishmeht of attached flow to the upper surface is strongly dependent upon pitch rate. The paper also contains a description of smoke flow visualisation tests. These were at a much lower Reynolds number than the pressure data tests, and consequently are of qualitative interest. Results of flow visualisation show that during a ramp-down test the near wake is much larger than in the corresponding static case, and that attachment is significantly delayed.
Asymptotic analysis of the classical aircraft stability equations
Authors: Graham W. R. 
Published: July 2016

AbstractA new approach to deriving analytical approximations for the free modes of motion of an aircraft is presented. Based on an asymptotic analysis, it eliminates the need for a priori assumptions regarding the characteristic motion of each mode, and is thus particularly suitable for an introductory exposition. In its basic form, it yields expressions for natural frequencies, damping factors and time constants which agree, to leading order, with well established results. At a more advanced level, it allows us to assess the validity of these results. In particular, we find that the two degree-of-freedom approximations to the short period oscillation and Dutch roll are asymptotically incorrect. This is unlikely to have a significant effect on the accuracy of the former, but is the reason for the poor damping predictions of the latter.
Optimisation of composite wind-tunnel wing models for frequency, flutter and divergence
Authors: Taylor J.M. , Butler R. , Harrison C. 
Published: July 2016

AbstractA comparison has been made between the composite beam designs produced by minimum mass optimisation using two different sets of constraints. The first approach constrained the design to have a given separation between fundamental bending and fundamental torsional natural frequencies; the second constrained the design to have a given flutter and divergence speed. The beams are modelled as a series of elements, stepped in thickness at discrete nodes, with the Dynamic Stiffness Method being used for calculation of their natural frequencies. The aeroelastic constraints are obtained from the Fortran program CALFUN. The results show that for similar flutter and divergence speeds, the optima produced using aeroelastic constraints have a slightly lower mass (up to 4% lower) and a less ‘hard’ flutter onset. However, the time taken to produce these optima is significantly longer (in excess of 2 orders of magnitude). A preliminary study discusses the merits of a combined optimisation method where frequency constrained optimisation is used to provide a near-optimum starting point for flutter and divergence constrained optimisation. In addition, a wind-tunnel model of one of the optima has been manufactured and subject to both modal analysis and wind-tunnel tests to validate the flutter speed calculations. This shows that when using strip theory, CALFUN predicts a conservative value of flutter speed for this design. Further investigation has shown CALFUN's lifting surface theory to be more accurate for low aspect ratio models.
Three-dimensional fibre optimisation with computer aided internal optimisation
Authors: Reuschel D. , Mattheck C. 
Published: July 2016

AbstractBig efforts have been made to optimise the behaviour and the properties of fibre reinforced materials. The fibre-matrix bonding, the influence of the fibre-matrix content and many other relations of several systems have been intensively investigated. Nevertheless, the arrangement of the fibres within a structure was a neglected subject of research.CAIO (computer aided internal optimisation) was developed to predict the optimal arrangement of fibres for given load and boundary conditions. The mechanism of the method has been adapted from biological structures. CAIO is based on the finite elements method (FEM). In a first step the force flow of a structure is calculated by using FEM. The CAIO routine changes orientation of orthotropic axes into the directions of force flow with respect to the FE-results. A following stress analysis leads to a reduced shear stress distribution. The optimum fibre arrangement is calculated by an automatically iterative process of alternating FE-run and CAIO calculation. The latest version of CAIO allows the calculation of the optimum fibre arrangement in three-dimensional shell structures as well as in three-dimensional volume structures.
The aerodynamic performance of paragliders
Authors: Babinsky H. 
Published: July 2016

AbstractAn analysis of paraglider performance has revealed that wing section drag is the most significant contribution to overall drag. Wind tunnel measurements performed on two-dimensional hollow models indicate that intake drag is less significant than previously thought. An experimental investigation into the characteristics of a ‘quasi ’ -two-dimensional flexible model consisting of solid ribs covered with a fabric skin was performed at realistic Reynolds numbers. The main cause of performance deterioration was found to be a significant reduction in section lift coefficient when compared to a similar solid wing section. This is believed to be mainly due to two factors: a large trailing edge separation and the deformation of the wing between ribs. The deformation was measured and it was shown that the deformed shape is less capable of generating high lift coefficients than the design section. It is thought that the extent of the trailing edge separation is increased due to the presence of streamwise grooves caused by the shape deformation of the wing. The shape of the separated region was found to be strongly three-dimensional with the separation point being about half a chord-length further upstream along the ribs. A small separation bubble was also observed immediately behind the lip of the intake, due to the fabric ‘flaring’ open. Based on the observations presented a number of suggestions for improved wings have been made.
Demonstration of cluster computing for three-dimensional CFD simulations
Authors: McMillan W. , Woodgate M. , Richards B. E. , Gribben B. J. , Badcock K. J. , Masson C. A. , Cantariti F. 
Published: July 2016

AbstractMotivated by a lack of sufficient local and national computing facilities for computational fluid dynamics simulations, the Affordable Systems Computing Unit (ASCU) was established to investigate low cost alternatives. The options considered have all involved cluster computing, a term which refers to the grouping of a number of components into a managed system capable of running both serial and parallel applications. The present work aims to demonstrate the utility of commodity processors for dedicated batch processing. The performance of the cluster has proved to be extremely cost effective, enabling large three dimensional flow simulations on a computer costing less than £25k sterling at current market prices. The experience gained on this system in terms of single node performance, message passing and parallel performance will be discussed. In particular, comparisons with the performance of other systems will be made. Several medium-large scale CFD simulations performed using the new cluster will be presented to demonstrate the potential of commodity processor based parallel computers for aerodynamic simulation.
Numerical solution of Euler equations for
aerofoils in arbitrary unsteady
motion
Authors: Lin C. Q. , Pahlke K. 
Published: July 2016

AbstractThis paper is part of a DLR research programme to
develop a three-dimensional Euler code for the
calculation of unsteady flow fields around
helicopter rotors in forward flight. The present
research provides a code for the solution of Euler
equations around aerofoils in arbitrary unsteady
motion. The aerofoil is considered rigid in motion,
and an O-grid system fixed to the moving aerofoil is
generated once for all flow cases. Jameson's finite
volume method using Runge-Kutta time stepping
schemes to solve Euler equations for steady flow is
extended to unsteady flow. The essential steps of
this paper are the determination of inviscid
governing equations in integral form for the control
volume varying with time in general, and its
application to the case in which the control volume
is rigid with motion. The implementation of an
implicit residual averaging with variable
coefficients allows the CFL number to be increased
to about 60. The general description of the code,
which includes the discussions of grid system, grid
fineness, farfield distance, artificial dissipation,
and CFL number, is given. Code validation is
investigated by comparing results with those of
other numerical methods, as well as with
experimental results of an Onera two-bladed rotor in
non-lifting flight. Some numerical examples other
than periodic motion, such as angle-of-attack
variation, Mach number variation, and development of
pitching oscillation from steady state, are given in
this paper.
Aerodynamic characteristics of delta wing–body combinations at high angles of attack
Authors: Viswanath P. R. , Patil S. R. 
Published: July 2016

AbstractAn experimental study investigating the aerodynamic characteristics of generic delta wing-body combinations up to high angles of attack was carried out at a subsonic Mach number. Three delta wings having sharp leading edges and sweep angles of 50°, 60° and 70° were tested with two forebody configurations providing a variation of the nose fineness ratio. Measurements made included six-component forces and moments, limited static pressures on the wing lee-side and surface flow visualisation studies. The results showed symmetric flow features up to an incidence of about 25°, beyond which significant asymmetry was evident due to wing vortex breakdown, forebody vortex asymmetry or both. At higher incidence, varying degrees of forebody-wing vortex interaction effects were seen in the mean loads, which depended on the wing sweep and the nose fineness ratio. The vortex breakdown on these wings was found to be a gradual process, as implied by the wing pressures and the mean aerodynamic loads. Effects of forebody vortex asymmetry on the wing-body aerodynamics have also been assessed. Comparison of Datcom estimates with experimental data of longitudinal aerodynamic characteristics on all three wing-body combinations indicated good agreement in the symmetric flow regime.
Some observations on the dynamic response to wing motion of the vortex burst phenomenon
Authors: Greenwell D. I. , Wood N. J. 
Published: July 2016

AbstractThe “post-stall” manoeuvre capabilities of current and projected combat aircraft have prompted a resurgence of interest in the dynamic response to wing motion of the vortex burst at high angles of attack. A large number of experimental studies have been reported, but these have tended to be restricted to a limited range of motion profiles and a single specific wing configuration. Presumably due to the complexity of the phenomenon, no attempt appears to have been made to undertake a systematic study of the burst response for a range of wing planforms and motion profiles. Hence, a survey was made of the published data and a semi-empirical correlation derived using a system identification methodology. For preliminary performance studies, the dynamic response of the vortex burst is modelled adequately by a second order lag transfer function. The physical significance of this system model and the implications for the design of a systematic experimental study are discussed.
A new approach in the analysis of linear systems with periodic coefficients for applications in rotorcraft dynamics
Authors: Wu D.-H. , Sinha S.C. 
Published: July 2016

AbstractA numerical technique for the stability analysis of linear mechanical dynamic systems with periodically varying parameters is proposed. The technique is based on representation of the solution vector in terms of Chebyshev polynomials defined over the principal period. Two formulations have been presented. The first formulation is suitable for systems described by state space equations, while the second can be applied directly to a set of second order equations with periodically varying mass, damping and stiffness matrices. As an illustrative example, the flap-lag stability of a multi-bladed rotor is examined. The numerical accuracy and efficiency of the proposed technique is compared with standard numerical codes based on Runge-Kutta, Adams-Moulton and Gear algorithms. The results indicate that the suggested approach is by far the most efficient one, particularly for systems with larger dimensions.
Three-dimensional vortex interactions with a stationary blade
Authors: Doolan C. J. , Coton F. N. , Galbraith R. A. McD. 
Published: July 2016

AbstractSurface pressure measurements were obtained during a three-dimensional vortex interaction with a NACA 0015 aerofoil. The upper and lower surfaces of the blade experienced different aerodynamic loads which appear to be controlled by the impact of the vortex axial core flow on the blade surface. On the upper surface of the blade, where the vortex core flow was away from the aerofoil, the interaction was characterised by the generation of a suction peak. On the lower surface, where the axial component was towards the blade, a pressure pulse developed and seemed to be influenced by the vortex approach angle. These features resulted in rapid changes in normal force and quarter chord pitching moment during the interaction. This impulsive loading of the blade may provide some explanation for sound generation and control degradation problems associated with the tail rotor of helicopters.
Investigation of the certification and operational procedures for turboprop aircraft in icing
Authors: Simpson M. P. , Render P. M. 
Published: July 2016

AbstractA study was conducted to identify possible improvements to the current certification and operational procedures for turboprop powered aircraft operating in icing conditions. Information was gathered through a series of interviews with airframe and engine manufacturers and also, operators and aircrews in Europe and Canada. The significant issues raised during the interviews are discussed, and a number of recommendations are made for future research and development activities in die area of aircraft icing. These recommendations identify the need for improved ice protection methods, enhanced thermodynamic models in ice prediction computer codes, and development of an ice prediction probe to warn aircrew that they will soon be entering icing conditions. Recommendations also include improvements to pilot training, and the need to make weather forecasts of icing more accurate and specific.
An analytical procedure for asymmetric store flutter
Authors: Liu J. K. 
Published: July 2016

AbstractA simple but effective method is presented to analyse the effects of asymmetric external stores on flutter of an aircraft in this paper. The method is a kind of ‘direction derivative’ technique, and can be easily applied to predict whether the asymmetric external stores increase or decrease the flutter speed. By using the present technique the varying tendency of flutter speed can be determined preliminarily. This can be very useful and valuable to the designers at the beginning stage of flutter analysis. The effectiveness of the proposed method is proved analytically.
The compound helicopter — why have we not succeeded before?
Authors: Orchard M. N. , Newman S. J. 
Published: July 2016

AbstractCompounding offers a way of advancing the performance of the standard helicopter significantly for a moderate increase in complexity through the addition of wings and/or auxiliary propulsion. The compound helicopter configuration has the potential advantages of increased speed, range, agility, productivity and reduced vibration levels over conventional helicopters. Despite several significant efforts, however, no compound helicopter has ever been put into production. This paper looks at three aircraft that came close to being accepted by operators and examines the reasons why they were not ultimately put into production. The cancellation of these projects appeared to be of a political nature rather than technical. Also addressed are the issues that still face prospective designers of compound helicopters and the lessons that can be extracted and applied to modern day efforts to build and sell an aircraft of this configuration.
Automated surface shape optimisation in the MDO project
Authors: Gould A. R. B. 
Published: July 2016

AbstractSurface shape optimisation was one of several topics researched under the multi-disciplinary optimisation (MDO) project. Several project partners participated in this activity which set out to develop, validate and demonstrate a number of technical issues related to automated shape design. Each of the participants brought together in-house and/or commercial analysis tools, a variety of different modelling and optimisation techniques, and common database and model generation methods. The objectives of this work were to validate the methodologies established in the preliminary MDO project phase and to demonstrate the optimisation process when applied to a simplified civil aircraft wing design problem. Several issues were central to the investigation, including alternative means of parametric descriptions for the wing surface shape, alternative optimisation strategies for wing MDO, and the impact of different levels of physical and geometrical modelling on MDO performance and resulting product optima. The outcomes of this work demonstrate the need for advanced analysis tools to be incorporated into aerospace vehicle design problems at a relatively early stage and highlight the dangers of over-simplification of the vehicle model.
Multidisciplinary design optimisation (MDO) methods: their synergy with computer technology in the design process
Authors: Sobieszczanski-Sobieski Jaroslaw 
Published: July 2016

AbstractThe paper identifies speed, agility, human interface, generation of sensitivity information, task decomposition, and data transmission (including storage) as important attributes for a computer environment to have in order to support engineering design effectively. It is argued that when examined in terms of these attributes the presently available environment can be shown to be inadequate. A radical improvement is needed, and it may be achieved by combining new methods that have recently emerged from multidisciplinary design optimisation (MDO) with massively parallel processing computer technology. The caveat is that, for successful use of that technology in engineering computing, new paradigms for computing will have to be developed - specifically, innovative algorithms that are intrinsically parallel so that their performance scales up linearly with the number of processors. It may be speculated that the idea of simulating a complex behaviour by interaction of a large number of very simple models may be an inspiration for the above algorithms; the cellular automata are an example. Because of the long lead time needed to develop and mature new paradigms, development should begin now, even though the widespread availability of massively parallel processing is still a few years away.