bluuebunny/crossref_metadata_2025_split huggingface dataset:
Numerical validation and back-pressure effect on internal compression flows of typical supersonic inlet
Authors: Ding F. , Shen C.-B. , Huang W. , Liu J. 
Published: February 2016

AbstractA numerical study was conducted to analyse the performance of different turbulence models and different turbulence intensities and turbulence length scales specified for the boundary condition of the inflow to the internal compression flow field of a typical supersonic inlet. The effect of the back-pressure ratio on the properties of the flow field was also investigated. Computational results obtained by the commercial software FLUENT, which is used to solve the full two-dimensional Reynolds-averaged Navier-Stokes equations, were validated through both graphical and quantitative comparisons with previously published experimental data. The two-equation models that were considered in this study are the RNGk-ε, realisablek-ε, standardk-ε, and SSTk-ω turbulence models. The RNGk-ε model had the best performance among the four models and predicted good wall pressure distributions. The best agreement between the predicted results and experimental data was obtained when either the default values of the freestream turbulence intensity and length scale in the FLUENT solver were used, or the empirical formula was used to calculate the two parameters of the freestream turbulence properties. The shock wave pattern varied between the oblique mode and the fully developed normal mode with increasing back-pressure ratio, and the unstart phenomenon occurred when the back-pressure ratio was sufficiently high.
Downstream evolution of wingtip vortices produced from an inverted wing
Authors: Barber T. , Kurts P. 
Published: February 2016

AbstractCounter-rotating vortices form from the opposite edges of lifting surfaces, and gradually move laterally and dissipate as they travel downstream (as seen in a wing-fixed reference frame). Under ground effect conditions, the vortex from a lifting wing – such as that used in an aircraft application – moves laterally outboard from the wingtip as it progresses downstream; for a downforce wing in ground effect – such as that used in an automotive application – the vortex moves laterally inboard. An interesting case is the situation where the inboard moving vortices become in close proximity to each other. The objective of the present study was to investigate counter-rotating vortices produced from a low aspect ratio downforce wing operating in ground effect. The pair of vortices move towards each other and mutually induce an upwards directed motion which in turn reduces the inboard movement driven by the ground effect. Experimental data gained from three-dimensional Laser Doppler Anemometry in a moving ground wind-tunnel was used to validate a Large Eddy Simulation computational result.
Maintenance test flying – an accident waiting to happen?
Authors: Poprawa S. 
Published: February 2016

AbstractThis paper focuses on maintenance test flying as pertaining to commercial jet aircraft. Aircraft maintenance manuals or regulatory prescriptions require aircraft to be test flown prior to being released to service, following specific maintenance, repair, overhaul or modification events. Further, such flights might be conducted to accept or return aircraft as demonstration of their serviceability. Similarly, test flights to verify aircraft performance are at times required.Such maintenance test flights are mostly conducted by pilots rated to fly those aircraft primarily in commercial line operations, typically with no or little training on such specific maintenance or performance test flight procedures or techniques. The international regulatory environment remains in flux with discussion ongoing.In conducting such flights a pilot is exposed to activities outside the normal aircraft standard operating procedures up to the edge of the operational flight envelope. Whilst not intentional, abnormal aircraft behaviour can nevertheless result in inadvertent flight outside the envelope with a consequential potential loss of control. History has shown that the predominant cause of fatal accidents during maintenance test flying result from complex loss of control scenarios not recovered or not recoverable. This raises the question of adequacy of pilot training.Maintenance test flights are a necessary component for the industry to maintain its exceptional safety standards and minimising loss of life. But such flights in themselves remain demonstrably one or two orders of magnitude more risky than commercial flights.
Experimental and numerical study of the flight of geese
Authors: Dimitriadis G. , Gardiner J. D. , Tickle P. G. , Codd J. , Nudds R. L. 
Published: February 2016

AbstractThe flight of barnacle geese at airspeeds representing high-speed migrating flight is investigated using experiments and simulations. The experimental part of the work involved the filming of three barnacle geese (Branta Leucopsis) flying at different airspeeds in a wind tunnel. The video footage was analysed in order to extract the wing kinematics. Additional information, such as wing geometry and camber was obtained from a 3D scan of a dried wing. An unsteady vortex lattice method was used to simulate the aerodynamics of the measured flapping motion. The simulations were used in order to successfully reproduce the measured body motion and thus obtain estimates of the aerodynamic forces acting on the wings. It was found that the mean of the wing pitch angle variation with time has the most significant effect on lift while the difference in the durations of the upstroke and downstroke has the major effect on thrust. The power consumed by the aerodynamic forces was also estimated; it was found that increases in aerodynamic power correspond very closely to climbing motion and vice versa. Root-mean-square values of the power range from 100W to 240W. Finally, it was observed that tandem flying can be very expensive for the trailing bird.
Constrained multi-objective aerofoil design using a multi-level optimisation strategy
Authors: Cameron L. , Early J. , McRoberts R. , Price M. 
Published: February 2016

AbstractA novel approach for the multi-objective design optimisation of aerofoil profiles is presented. The proposed method aims to exploit the relative strengths of global and local optimisation algorithms, whilst using surrogate models to limit the number of computationally expensive CFD simulations required. The local search stage utilises a re-parameterisation scheme that increases the flexibility of the geometry description by iteratively increasing the number of design variables, enabling superior designs to be generated with minimal user intervention. Capability of the algorithm is demonstrated via the conceptual design of aerofoil sections for use on a lightweight laminar flow business jet. The design case is formulated to account for take-off performance while reducing sensitivity to leading edge contamination. The algorithm successfully manipulates boundary layer transition location to provide a potential set of aerofoils that represent the trade-offs between drag at cruise and climb conditions in the presence of a challenging constraint set. Variations in the underlying flow physics between Pareto-optimal aerofoils are examined to aid understanding of the mechanisms that drive the trade-offs in objective functions.
Preliminary flight test correlations of the X-HALE aeroelastic experiment
Authors: Jones J. R. , Cesnik C. E. S. 
Published: February 2016

AbstractAn experimental, remotely-piloted aircraft has been designed and fabricated at University of Michigan that is aeroelastically representative of very flexible aircraft. Known as X-HALE, this Experimental High-Altitude Long-Endurance aircraft exhibits geometrically nonlinear behaviour and displays specific aeroelastic characteristics designed into the experiment. This paper presents the data from the initial flight tests of the lightly instrumented X-HALE Risk Reduction Vehicle that confirm the expected aeroelastic characteristics. This opens the way for future flight tests with a fully-instrumented platform which will provide data to support validation of coupled, nonlinear aeroelastic/flight dynamic codes.
Separation investigation of endo-atmospheric multi-stage space probe
Authors: Samani M. , Ghapanvary M. A. 
Published: February 2016

AbstractThis paper deals with selection and analysis of two-stage endo-atmospheric separation of supersonic parachute of a test projectile. Flight scenario reads that after the motor burns out, it is separated from the projectile, a few moments after which the parachute is ejected out of the payload and set in the open mode. It is important to study the modes of the stages involved and set a safe distance between them. As this process involves some random variables and needs more time, a shortcut statistical method has been employed in uncertainty variables functions to carry out the analysis. It is meant to take appropriate measures in order for the separation to be collision-free and safe. To do so, relative position of the two stages are modelled and simulated. A statistical method is employed to analyse the relative distance between the two stages in critical points. The results reflect that a safe distance is maintained in the stage of parachute deployment and after supersonic parachute is employed. In addition the said analysis is also carried out via Monte Carlo method. Comparison of the results of these two methods is indicative of a small error. The statistical method is validated and sufficient knowledge on relative attitudes of the stages is obtained.
Rotorcraft-pilot coupling analysis through state-space aerodynamic modelling
Authors: Serafini J. , Greco L. , Gennaretti M. 
Published: February 2016

AbstractThe terminology ‘rotorcraft-pilot coupling’ denotes phenomena arising from interaction between pilot and rotorcraft. Among these, the present work deals with ‘pilot-assisted oscillations’ that derive from unintentional pilot actions on controls due to seat vibrations, and are strictly related to rotor-aeroelasticity/airframe-structural-dynamics coupling, with involvement of blade control actuator dynamics. Focusing the attention on helicopters, a comprehensive rotorcraft model is developed and applied, with main rotor unsteady aerodynamics described in state-space form. This makes it particularly suited for stability and frequency-response analysis, as well as control applications. Numerical investigations address two critical rotorcraft-pilot coupling aeroelastic issues: stability of vertical bouncing and gust response in hovering. Results from main rotor unsteady aerodynamics modelling are compared with widely-used quasi-steady aerodynamics predictions. These suggest that, for accurate RPC/PAO phenomena predictions, mathematical modelling should include the three-dimensional, unsteady-flow effects, and that the pilot-in-the-loop passive behaviour produces a beneficial effect on the load factor generated by gust encountering.
Total pressure distortion levels at the aerodynamic interface plane of a military aircraft
Authors: Triantafyllou T. , Nikolaidis T. , Diakostefanis M. , Pilidis P. 
Published: February 2016

AbstractMilitary aircrafts are often subjected to severe flight maneuvers with high Angles-of -Attack (AOA) and Angles of Sideslip (AOSS). These flight attitudes induce non-uniform in flow conditions to their gas turbine engines which may include distortion of inlet total pressure and total temperature at the Aerodynamic Interface Plane (AIP). Operation of the downstream compression system with distorted inflow typically results in reduced aerodynamic performance, reduced stall margin, and increased blade stress levels. In the present study the steady state total pressure distortion induced to the Aerodynamic Interface Plane due to the aircraft’s flight attitude have been estimated in terms of distortion descriptors. The distorted conditions at the interface between the intake and the engine have been predicted by using Computational Fluid Dynamics (CFD), where 33 different aircraft flight attitudes have been tested. Based on the obtained results the effect of Angle-of-Attack (AOA) and Angle of Side Slip (AOSS) on the distortion descriptors have been studied. The results showed that the distortion effect becomes more pronounced whenever this specific airframe configuration is exposed to incoming flow with an AOSS. Among the tested cases, the greatest total pressure defect at the AIP in terms of difference from the average value and of circumferential extent was calculated for the flight attitudes of 0·35M flight with 0° AOA and 8° AOSS and 0·35M fight with 16° AOA and 16° AOSS.
Predicting the certification basis for airliner air-to-air refuelling
Authors: Spencer R. J. 
Published: February 2016

Abstract
The premise is that in the future civil Air-to-Air Refuelling (AAR) will become an economic necessity if popular mass air travel is to continue. What is attempted is to provide a contemporary view of how such future operations could be safely undertaken. The intention is to predict the certification basis for demonstrating safe AAR operation of Cruiser-Feeder concepts. The necessary systems and aircraft functions are treated very much as they are today when civil certifying a large aeroplane type. The compliance demonstration required for environmental conditions, flight envelope, systems providing the necessary functionality, structural integrity, weight and balance are discussed.
Applicable existing civil certification requirements are identified and where necessary expanded in scope to accommodate AAR operation. Where contemporary material does not supply appropriate guidance then corresponding safety criteria are proposed to address the deficiency. Lessons learnt from military AAR include the drive for interoperability. This has resulted in extensive efforts to standardise equipment and systems, which are equally applicable to civil AAR. Extremely useful advisory material exists, ranging from flight testing techniques to related safety.
The importance of ensuring the consistency of failure condition categorisation at system and aircraft level is highlighted. The treatment of failures when two aircraft are in close proximity is something not considered by civil functional hazard analysis. The concept of AAR as an additional flight phase is introduced and affected system safety analyses identified. Examples of failure conditions that are not catastrophic at system level, but potentially could be at aircraft level during AAR are provided. Rendezvous scenarios are described to illustrate their influence on the certification basis. Combining such considerations with the factors that influence aircraft design leads to ramifications for handling qualities, performance and fuel system design. A viable and certifiable AAR configuration is consequently proposed. Consideration is given to treating operational certification in a progressive manner similar to existing LROPS (Long Range Operations).
3D UAV trajectory planning using evolutionary algorithms: A comparison study
Authors: Bagherian M. , Alos A. 
Published: February 2016

Abstract
This paper focuses on the three dimensional flight path planning for an unmanned aerial vehicle (UAV) on a low altitude terrain following\terrain avoidance mission. The UAV trajectory planning problem is to compute an optimal or near-optimal trajectory for a UAV to do its mission objectives in a surviving penetration through the hostile enemy environment, considering the shape of the earth and the kinematics constraints of the UAV. Using the three dimensional terrain information, three dimensional flight path from a starting point to an end point, minimising a cost function and regarding the kinematics constraints of the UAV is calculated. The geographic information of the earth shape and enemy locations is generated using digital terrain model (DTM) and geographic information system (GIS), and is displayed in a 3D environment. Using 3D-maps containing the geographic data accompanied by DTM, and GIS, the problem is modelled by deriving the motion equations of the UAV. Two heuristic algorithms are proposed for this problem: genetic and particle swarm algorithms. Genetic and particle swarm algorithms are general purposes algorithms, because they can solve a wide range of problems, so they have to be adjusted to solve the trajectory planning problem. To test and compare the paths obtained from these algorithms, a software program is built using GIS tools and the programming languages C# and MATLAB.
An efficient method for predicting zero-lift or boundary-layer drag including aeroelastic effects for the design environment
Authors: Camberos J. A. , Kolonay R. M. , Eastep F. E. , Taylor R. F. 
Published: February 2016

AbstractOne of the aerospace design engineer’s goals aims to reduce drag for increased aircraft performance, in terms of range, endurance, or speed in the various flight regimes. To accomplish this, the designer must have rapid and accurate techniques for computing drag. At subsonic Mach numbers drag is primarily a sum of lift-induced drag and zero-lift drag. While lift-induced drag is easily and efficiently determined by a far field method, using the Trefftz plane analysis, the same cannot be said of zero-lift drag. Zero-lift drag (CD,0) usually requires consideration of the Navier-Stokes equations, the solution of which is as yet unknown except by using approximate numerical techniques with computational fluid dynamics (CFD). The approximate calculation of zero-lift drag from CFD is normally computed with so-called near-field techniques, which can be inaccurate and too time consuming for consideration in the design environment. This paper presents a technique to calculate zero-lift and boundary-layer drag in the subsonic regime that includes aeroelastic effects and is suitable for the design environment. The technique loosely couples a two-dimensional aerofoil boundary-layer model with a 3D aeroelastic solver to compute zero-lift drag. We show results for a rectangular wing (baseline), a swept wing, and a tapered wing. Then compare with a rectangular wing with variable thickness and camber, thinning out from the root to tip (spanwise direction), thus demonstrating the practicality of the technique and its utility for rapid conceptual design.
Night-time offshore helicopter operations: a survey of risk levels per phase of flight, flying recency requirement and visual approach technique
Authors: Nascimento F. A. C. , Majumdar A. , Ochieng W. Y. , Schuster W. 
Published: February 2016

AbstractThe analysis of risks per phases of flight is fundamental for safe helicopter operations, of which night-time offshore oil- and gas-related missions form an important part. The safe execution of such missions also depends on pilots’ recent flying practice and a stable visual approach segment prior to landing. However, the poor quality of the safety data currently available prevents accurate analysis of risk on a per-phase-of-flight basis, establishment of a meaningful flying recency requirement and identification of any preferable visual approach design. To redress these problems, this paper develops a bespoke taxonomy of phases of offshore helicopter flights and uses it as the basis for a questionnaire survey on the phase-specific risk levels experienced by pilots in the night-time, perceived optimal flying recency requirement and preferred visual approach design. With the responses obtained from pilots located in seven countries, extensive statistical hypothesis testing shows that the phases involving visual scan techniques at high speed regimes are problematic, especially the visual segment of instrument approaches. Moreover, the between-night-flights time gaps required for assured flying recency were found considerably shorter than currently standardised across the industry. Finally, no preferred visual approach technique was identified. A number of important implications have been highlighted and should form the basis for future safety interventions.
Serum concentrations of 25-hydroxyvitamin D and its association with bone mineral density and serum parathyroid hormone levels during winter in urban males from Guiyang, Southwest China
Authors: Zhang Qiao , Shi Lixin , Peng Nianchun , Xu Shujing , Zhang Miao , Zhang Song , Li Hong , Zhuang Huijun , Gong Mingxian , Wu Danrong , Wang Rui 
Published: February 2016

AbstractSerum vitamin D (25-hydroxyvitamin D (25OHD)) may influence serum parathyroid hormone (PTH) levels and bone mineral density (BMD). In the present study, we assessed serum 25OHD concentration and its association with PTH and BMD in urban males from Guiyang (N26.57°), the capital city of Guizhou province, Southwest China. We recruited 634 males aged >20 years from the Guiyang Health Measures Survey, and stratified them into three groups according to age: young (20–39 years), middle aged (40–59 years) and older (60–79 years). We measured serum concentrations of 25OHD, PTH levels and BMD of the lumbar spine (L1–L4), femoral neck and total hip. In addition, we also explored the relationship between 25OHD and lifestyle, socio-economic characteristics and medical history by applying covariance analysis and locally weighted regression plots. The results showed that serum 25OHD was <50 nmol/l in 59·3 % of the subjects and >75 nmol/l in 12·6 % of the subjects. Higher level of serum PTH was detected in relation to lower concentrations of serum 25OHD up to 50 nmol/l. A negative correlation between serum 25OHD and PTH concentrations was observed (r −0·207, P=0·003). Mean concentration of serum PTH increased gradually and plateaued while concentrations of serum 25OHD decreased to 50 nmol/l. Gradual increase in serum PTH was observed as 25OHD concentration was <25 nmol/l (P=0·004). BMD values at all sites were greater in the higher serum 25OHD concentration group. This study shows that low concentrations of serum 25OHD were common in males, and bone health was likely to be improved when serum 25OHD values were between 30 and 50 nmol/l.
Assessment of nasal mucociliary activity in patients with Behçet's disease
Authors: Ozbay I , Kucur C , Temİzturk F , Ozkan Y , Kahraman C , Oghan F 
Published: February 2016

AbstractObjective:To investigate nasal mucociliary clearance in patients with Behçet's disease.Methods:Thirty patients with Behçet's disease, diagnosed on the basis of criteria defined by the International Study Group for Behçet's Disease, and 30 healthy individuals were recruited. In both groups, individuals with conditions that could affect nasal mucociliary clearance were excluded. Nasal mucociliary clearance time was evaluated using saccharin tests. The time between placement of a saccharin tablet and the tasting of the saccharin was measured and recorded as the saccharin clearance time.Results:The mean nasal mucociliary clearance time was significantly longer in the Behçet's disease patients than in the control subjects (p < 0.001). Furthermore, there was a positive correlation between Behçet's disease duration and nasal mucociliary clearance time (p < 0.001, r = 0.882).Conclusion:The results suggest that nasal mucociliary clearance time is longer in Behçet's disease patients than in control subjects, and is positively correlated with disease duration.