bluuebunny/crossref_metadata_2025_split huggingface dataset:
Self-cleaning barrier filter for rotorcraft engines
Authors: Bojdo N. , Filippone A. 
Published: February 2016

AbstractA parameter-based study of a novel self-cleaning barrier filter concept for rotorcraft engines is presented. Existing engine inlet barrier filters for rotorcraft achieve a high separation efficiency (up to 99% for a dust resembling a coarse test dust) at the expense of a pressure drop that increases over time. Other engine protection devices with invariant pressure loss signals cannot offer the same level of efficiency. Furthermore, inlet barrier filters are absent on rotorcraft with larger mass flow demands, due to larger filtration area required. This work proposes a solution that addresses each of these limitations, and establishes the parametric framework upon which such a design could be realised. The drum-shaped self-cleaning barrier filter is affixed to the engine inlet and spins about its longitudinal axis, such that each of its fibrous filter pleats can be cleaned once per cycle. An initial increase of pressure loss gives way to a period of sustained invariance. The key parameters are the internal particle capacity of the chosen filter medium and the speed of rotation. Other design parameters can be optimised to yield minimum pressure drop for given set of flow conditions.
Qualification of the ARA TWT for laminar flow testing
Authors: Allen N. , Lawson S. , Maina M. , Alderman J. 
Published: February 2016

AbstractThe current drive towards reducing the environmental impact of aircraft necessitates the ability to evaluate techniques for promoting natural laminar flow in a large scale wind tunnel facility. A test was undertaken on the M2355 variable sweep model to obtain temperature sensitive paint (TSP) and hot-film data from which the transition locations at a range of sweep angles and flow conditions could be identified. The TSP technique has been shown to be a reliable method for determining transition on suitably treated wind tunnel models. Pressure data were also acquired and interpolated to provide the input to the laminar boundary layer code, BL2D, the output from which was used in the linear stability analysis code, CoDS, to calculate the N-factor for the ARA TWT (Transonic Wind Tunnel) facility. Two sets of N-factors were calculated, firstly using incompressible analysis with stationary crossflow and secondly using compressible analysis with travelling crossflow. In both analyses the Tollmien-Schlichting and crossflow cases were calculated together, rather than separating the cases before running the analysis. The resulting N-factors indicate a degree of scatter typical for experimental data. The N-factor based on incompressible theory for crossflow was found to be approximately 7 and for Tollmien-Schlichting (T-S), approximately 11. The results of the wind tunnel test and the analysis carried out are considered to be the first steps towards establishing a methodology for performance testing, in atmospheric tunnels such as the TWT, for aircraft designed to have significant regions of laminar flow. The project has also provided a body of experimental test data which will be valuable for future research into development and validation of laminar flow methods.
Structural health monitoring technology for a full-scale aircraft structure under changing temperature
Authors: Gao D. , Wang Y. , Wu Z. , Rahim G. 
Published: February 2016

AbstractThis paper presents optimal operating modes for the factors to maximise the detection capability of a given SHM technology in service environment. Firstly, an orthogonal experiment was performed to determine the importance ranking of the influence factors. Through the test, it is found that operating temperatures for SHM hardware and excitation frequencies for PZT actuator were the most critical factors. Then, numerical model of Lamb waves generated and received by PZT sensors were presented to predict the distribution of response signal amplitudes under changing temperature. Verification tests were carried out on a glass fibre reinforced composite plate at different temperatures. The comparison between the analytical prediction and test results was presented and temperature-dependent optimal frequencies for PZT actuators were obtained. Finally, SHM experiments of full-scale horizontal composite structures are presented. The detection capability of the SHM technology applications of aircrafts in real world is verified by the experimental results.
Optimising the roll-sway motion cues available from a short stroke hexapod motion platform
Authors: Hodge S.J. , Perfect P. , Padfield G.D. , White M.D. 
Published: February 2016

AbstractThis paper presents findings from research conducted at the University of Liverpool aimed at optimising the motion cues available from a short-stroke hexapod motion platform. Piloted simulations were conducted for a typical helicopter low-speed sidestep manoeuvre. To correctly simulate the sidestep manoeuvre the motion platform must translate laterally at the same time as it rolls. If the motion in these two axes is not properly harmonised then the pilot can experience significant false motion cues. This is a particular concern for short-stroke hexapod platforms, where displacement limits can severely constrain the available lateral travel particularly during motion in multiple axes (e.g. roll and sway). During the experiment the motion filter gains in the roll and sway axes and the roll-axis motion filter break-frequency were varied. Objective and subjective measures of pilot performance and motion fidelity were gathered for each motion filter configuration, the latter using a new motion fidelity rating scale. The key findings show that acceptable motion cues could only be achieved by careful harmonisation of the motion filter gains in the roll and sway axes. A high gain in the roll axis coupled with a low gain in the sway axis resulted in motion which was abrupt and uncomfortable. On the other hand, too large a gain in the sway axis resulted in extreme lateral displacements of the motion platform leading to undesirable side-effects. The phase distortion between the visual and platform motion cues, introduced by the roll-axis motion filter, also had a significant impact on the pilot’s perception of motion fidelity. These results are presented in the form of proposed motion fidelity criteria for short-stroke hexapod platforms and compared with results from previous research conducted on a range of large motion systems.
An integrated methodology to assess the operational and environmental performance of a conceptual regenerative helicopter
Authors: Ali F. , Goulos I. , Pachidis V. 
Published: February 2016

AbstractThis paper aims to present an integrated multidisciplinary simulation framework, deployed for the comprehensive assessment of combined helicopter–powerplant systems at mission level. Analytical evaluations of existing and conceptual regenerative engine designs are carried out in terms of operational performance and environmental impact. The proposed methodology comprises a wide-range of individual modeling theories applicable to helicopter flight dynamics, gas turbine engine performance as well as a novel, physics-based, stirred reactor model for the rapid estimation of various helicopter emissions species. The overall methodology has been deployed to conduct a preliminary trade-off study for a reference simple cycle and conceptual regenerative twin-engine light helicopter, modeled after the Airbus Helicopters Bo105 configuration, simulated under the representative mission scenarios. Extensive comparisons are carried out and presented for the aforementioned helicopters at both engine and mission level, along with general flight performance charts including the payload-range diagram. The acquired results from the design trade-off study suggest that the conceptual regenerative helicopter can offer significant improvement in the payload-range capability, while simultaneously maintaining the required airworthiness requirements. Furthermore, it has been quantified through the implementation of a representative case study that, while the regenerative configuration can enhance the mission range and payload capabilities of the helicopter, it may have a detrimental effect on the mission emissions inventory, specifically for NOx(Nitrogen Oxides). This may impose a trade-off between the fuel economy and environmental performance of the helicopter. The proposed methodology can effectively be regarded as an enabling technology for the comprehensive assessment of conventional and conceptual helicopter-powerplant systems, in terms of operational performance and environmental impact as well as towards the quantification of their associated trade-offs at mission level.
Water injection pre-compressor cooling assist space access
Authors: Mehta U. , Bowles J. , Melton J. , Huynh L. , Hagseth P. 
Published: February 2016

AbstractAdvances in space activity are linked to reductions in launch cost. Air-breathing propulsion-assisted flight systems offer the potential for revolutionary change of the space operations paradigm. Horizontal launch of a space-access system provides mission flexibility, responsiveness, and affordability. One way to reduce launch cost is to increase the Mach number at which a launch vehicle is staged from a carrier aircraft. Without exceeding the engine and airframe design limits, the pre-compressor cooling technology allows an operational aircraft to operate at Mach numbers and altitudes beyond its basic operational limits. This is an essential, near-term technology for reducing launch cost to place small-weight payloads in low Earth orbit. The advantage of this technology is assessed with a modified McDonnell Douglas QF-4C aircraft. Payloads are unachievable or marginal with an unmodified QF-4C. However, payloads weighing around 150 pounds are plausible with this aircraft when incorporating the water injection pre-compressor cooling (WIPCC) technology.
Flight in nature II: How animal flyers land
Authors: Manzanera R.A. Jiménez , Smith SH. 
Published: February 2016

AbstractIn this review paper, different landing strategies of diverse species of animal flyers and gliders, both extinct and extant, are analysed. These methods vary depending on the animal group and the sensory system used by the animal to detect its landing site. In almost all species the use of delayed stall during the landing manoeuvre was observed. Sometimes wing flapping was used to aid in deceleration. With respect to guidance and navigation, most insect, bird and mammal gliders use their vision to guide them to landing via optical flow or motion parallax. Bats, which are nocturnal creatures, rely on their auditory system as they use echolocation to find their nesting site. Some butterfly and moth species guide themselves to landing using their olfactory sense as they follow pheromone trails. The information presented here can be used as a source of information for novel bio-inspired unmanned aircraft design.
Flexible rotor blade dynamics for helicopter aeromechanics including comparisons with experimental data
Authors: Goulos I. , Pachidis V. , Pilidis P. 
Published: February 2016

AbstractThis paper presents the development of a mathematical model for the implementation of flexible rotor blade dynamics in real-time helicopter aeromechanics applications. A Lagrangian approach is formulated for the rapid estimation of natural vibration characteristics of nonuniform rotor blades. A matrix/vector formulation is proposed for the treatment of elastic blade kinematics in the time-domain. In order to overcome the classical hurdles of time-accurate simulation and establish applicability in real-time, a novel, second-order accurate, finite-difference scheme is employed for the numerical discretisation of elastic blade motion. The proposed rotor dynamics model is coupled with a finite-state induced flow and an unsteady blade element aerodynamics model. The combined formulation is implemented in a helicopter flight mechanics simulation code. The integrated approach is deployed in order to investigate rotor blade resonant frequencies, trim control angles, oscillatory blade loads and induced vibration for a hingeless and an articulated helicopter rotor. Extensive comparisons are carried out with wind tunnel and flight test measurements, and non-real-time comprehensive analysis methods. Good agreement with measured data is exhibited considering primarily the low-frequency harmonic components of oscillatory loading. It is shown that, the developed methodology can be utilised for real-time simulation on a typical computer with sufficient modelling fidelity for accurate estimation of oscillatory blade loads.
The effect of the aerofoil thickness on the performance of the MAV scale cycloidal rotor
Authors: Hu Y. , Zhang H.L. , Tan C. 
Published: February 2016

AbstractThe numerical simulations for cycloidal propellers based on five aerofoils with different thickness are presented in this paper. The CFD simulation is based on sliding mesh and URANS. The results of CFD simulation indicates that all test cases share similar flow pattern. There are leading edge vortex and trailing-edge vortex due to blade dynamic stall. Interaction between the vortices shed from upstream blade and the downstream blade can be observed. There is variation of blade relative inflow velocity due to downwash in the cycloidal rotor cage. These factors result in large fluctuations of the aerodynamics forces on the blade. The comparison of the forces and flow pattern indicates that the thickness and leading edge radius of the aerofoil can significantly influent the flow pattern and hence the performance of the cycloidal propeller.
Instrumented splashdown testing of a scale model Titan Mare Explorer (TiME) capsule
Authors: Lorenz R. D. , Hibbard K. , Paul M. V. , Walsh J. , Olds D. W. , Willits S. , Bierhaus E. B. , Kretsch W. E. 
Published: February 2016

AbstractWater entry tests are conducted with a scale model capsule to explore the sensitivity of splashdown accelerations and motions to impact conditions, to support estimation of splashdown loads and behaviours of the proposed Titan Mare Explorer (TiME) mission. A 3D printed capsule with off-the-shelf USB accelerometer loggers enabled tests to be performed on a tight schedule. Contact impulse and peak loads are presented for a range of impact speeds and geometries, and predicted loads at full-scale on Titan are derived. The observed variation of peak load with impact speed is broadly consistent with the theoretically-expected square law but is surprisingly also consistent with a linear function (in common with some results from the literature). Test execution procedures and the performance of the data acquisition system are reviewed.
Turboprop aircraft noise: Advancements and comparison with flyover data
Authors: Filippone A. 
Published: February 2016

AbstractThis paper contributes to the prediction of aircraft noise. The framework of our study is based on a comprehensive analysis, which includes sub-models for airframe, propulsion and propeller noise. The sources models are complemented by various accounts of interference phenomena, including fuselage scattering, propeller shielding, wing and flap effects. The propagation of the acoustic pressures from the noise sources is done through a number of additional sub-models, which include spherical spreading, Doppler effects, ground reflection, shear winds and temperature gradients through the atmosphere. We present some fly-over noise data. The data include measurements by 13 microphones at community locations, meteorological data, and flight recorder data packs, which provide the complete state of the aircraft along the noise trajectory. Examples of verification are shown for the turboprop airplane Dash8-Q400, both on approach and departure. A sensitivity analysis is carried out to investigate the importance of the uncertainty effects, which are split between internal (aircraft and propulsion), external (atmospheric environment), and aircraft position.
Experimental investigation of the rotor-wing aerodynamic interaction in a tiltwing aircraft in hover
Authors: Droandi G. , Zanotti A. , Gibertini G. , Grassi D. , Campanardi G. 
Published: February 2016

AbstractThe hovering performance and the lifting capability of tiltrotor aircraft are strongly affected by the aerodynamic interaction between wing and rotors. The tiltwing concept represents a promising technology to increase the hover performance by reducing the wing-rotor interference. The present work describes an experimental activity carried out on a ¼ scaled tiltwing aircraft half-model to achieve a detailed insight about the main issues characterising the aerodynamic interaction between wing and rotor in hover. The results of the experimental campaign, including both force measurements and Particle Image Velocimetry surveys, enabled to evaluate both the aircraft performance for different configurations of the tilting wing and to achieve a detailed insight about the flow physics of the rotor wake in the interaction with the wing. The test activity provided a comprehensive experimental database that was obtained over a not confidential aircraft configuration.
Numerical investigation of secondary flows in a constant-width wind-tunnel contraction
Authors: Bouriga M. , Taher R. , Morency F. , Weiss J. 
Published: February 2016

AbstractThe flow inside a constant-width wind-tunnel contraction is simulated by solving the Reynolds-Averaged Navier-Stokes equations with an eddy-viscosity turbulence model. The results show the presence of longitudinal vortices near the sidewalls centreline. This confirms a former hypothesis involving the generation of skew-induced longitudinal vorticity within the sidewalls boundary layers. Detailed analysis reveals that the flow structure is influenced by viscous effects in the boundary layers and streamline curvature in the potential flow. Three-dimensional boundary-layer profiles on the contraction sidewall are analysed in the framework of the streamline co-ordinate system and its associated hodographic diagram. The resulting profiles help understand the generation of secondary flows and the associated longitudinal vorticity.
Effects of surface flow visualisation on aerodynamic loads at low Reynolds number
Authors: Traub L. W. , Waghela R. , Botero E. M. 
Published: February 2016

AbstractIn this article, the effect of on-surface flow visualisation (SVF) techniques on measured loads over an airfoil are explored. Titanium dioxide based mixture effects on the lift and drag coefficient are experimentally quantified at low Reynolds numbers by recording the time history as the patterns evolve and freeze. With statistical comparison based on Student’s t-distribution method, it was determined that the effect on the drag coefficient was minimal but the lift coefficient was slightly attenuated. Additionally, it was observed that at high angles-of-attack the temporal history of the flow as the wind tunnel ramps up may alter the steady-state flow field in the presence of a SFV mixture.
Experimental and numerical study of mixing characteristics of a rectangular lobed mixer in supersonic flow
Authors: Feng J.-H. , Shen C.-B. , Wang Q.-C. , Lei J. 
Published: February 2016

AbstractA combined experimental and computational study on a rectangular lobed mixer is performed. A series of simulations based on a steady Reynolds-averaged Navier-Stokes Simulation (RANS) are conducted to analyse the mixing mechanisms of large-scale streamwise structure shed by the trailing edge of lobed mixer, with emphasis being placed on the effect of turbulence modeling and inflow conditions. The simulations are validated in respect of velocity and scalar distribution against the data obtained through Particle Image Velocimetry (PIV) and Nanoparticle-based Planar Laser Scattering (NPLS) technique. The computational results predicted by the SSTk–ω turbulence model show better agreement with the experimental data. But the small-scale turbulence structures are not captured accurately by these turbulence models. The convoluted shear layer shed from trailing edge is stretched and rotated by the large-scale streamwise vortices, forming an unstable ‘pinching-off’ structure, which increases the interfacial area. And at the interface of two streams, a large number of small-scale turbulence structures are formed, which contribute a lot to the mixing enhancement along with the increased interfacial area. The streamwise vorticity decays more rapidly with the decrease of velocity ratio and total pressure ratio of two streams. The scalar thickness which reflects the mixing rate of two streams increases with the decreasing velocity ratio and total pressure ratio.
Aerodynamic modelling of fin stabilised underslung loads
Authors: Enciu K. , Rosen A. 
Published: February 2016

AbstractBox-like slung loads exhibit periodic yaw response instabilities, while carried externally by a helicopter. When coupled with the slung load longitudinal and lateral pendulum motions, these instabilities result in significant pendulum oscillations of the load. High amplitude oscillations lead in many cases to the limiting of a load’s flight envelope. Using wind tunnel and flight tests, rear mounted fins were previously demonstrated as efficient means for stabilisation of a problematic load. However, the lack of a proper analytical model of the stabilised load’s aerodynamic characteristics, led to a trial and error development process, without an appropriate physical understanding of the stabilisation problem. The present paper describes a method for the aerodynamic modeling of fins stabilised slung loads based on a limited number of simple static wind-tunnel tests. The resulting database is incorporated in a dynamical slung load simulation that shows good agreement with dynamic wind-tunnel tests. The applicability of the proposed method is demonstrated, by the calculation of stabilised loads aerodynamic databases for interim fin inclination angles not covered by tests.
Autonomous visual recognition of known surface landmarks for optical navigation around asteroids
Authors: Rowell N. , Dunstan M. N. , Parkes S. M. , Gil-Fernández J. , Huertas I. , Salehi S. 
Published: February 2016

AbstractWe present an autonomous visual landmark recognition and pose estimation algorithm designed for use in navigation of spacecraft around small asteroids. Landmarks are selected as generic points on the asteroid surface that produce strong Harris corners in an image under a wide range in viewing and illumination conditions; no particular type of morphological feature is required. The set of landmarks is triangulated to obtain a tightly fitting mesh representing an optimal low resolution model of the natural asteroid shape, which is used onboard to determine the visibility of each landmark and enables the algorithm to work with highly concave bodies. The shape model is also used to estimate the centre of brightness of the asteroid and eliminate large translation errors prior to the main landmark recognition stage. The algorithm works by refining an initial estimate of the spacecraft position and orientation. Tests with real and synthetic images show good performance under realistic noise conditions. Using simulated images, the median landmark recognition error is 2m, and the error on the spacecraft position in the asteroid body frame is reduced from 45m to 21m at a range of 2km from the surface. With real images the translation error at 8km to the surface increases from 107m to 119m, due mainly to the larger range and lack of sensitivity to translations along the camera boresight. The median number of landmarks detected in the simulated and real images is 59 and 44 respectively. This algorithm was partly developed and tested during industrial studies for the European Space Agency’s Marco Polo-R asteroid sample return mission.