bluuebunny/crossref_metadata_2025_split huggingface dataset:
Hypermanoeuvrability and visual cloaking: new adaptive aerostructures technologies for UAVs
Authors: Barrett R. 
Published: February 2016

AbstractThe paper begins with a summary of the performance characteristics of the most important classes of adaptive aerostructures which are relevant for UAVs and the materials which drive them. The paper describes several classes of UAVs that take advantage of the various kinds of adaptive aerostructures technologies. These technologies are shown to be suitable for very small and even hard-launched UAVs, hovering, high speed, low speed and convertible UAVs (i.e. UAVs that can transition between helicopter and aircraft/missile flight modes). The first class of UAVs presented highlights newly invented post-buckled precompressed (PBP) actuators which are particularly well suited to enhancing convertible coleopters or ‘ultra-high performance UAVs.’ These UAVs are capable of hovering for extended periods of time as a helicopter in gusty, windy, dusty, real tactical environments, then popping up, converting and dashing out like a missile at several hundred knots. The paper shows photos (i.e. no computer simulations) of convertible coleopter launches from armoured vehicles, a battle-damage assessment exercise and a live fire sequence with 40mm munitions. The paper concludes with a description of the visual signature suppression (VSS) system which was employed on a 2m UAV. The VSS system was shown to suppress the visual cross section to below 1·8cm2 which is the threshold for human aircraft observation. Accordingly, VSS equipped aircraft are said to ‘disappear’ in mid flight.
A comprehensive numerical study of battle damage and repairs upon the aerodynamic characteristics of an aerofoil
Authors: Saeedi M. , Ajalli F. , Mani M. 
Published: February 2016

AbstractA NACA 641-412 aerofoil with circle and star damage and also three repair configurations has been numerically investigated. Two different methods of mesh generation were employed: multi structured mesh for the star damaged aerofoil and unstructured mesh for the other aerofoils. The results show that the damage will cause a reduction in lift coefficient of the aerofoil and also a different stall angle relative to that of the undamaged aerofoil. Each kind of repair improves the aerodynamic characteristics of the aerofoil considerably. The flow Field inside the damage hole and the cavity caused by the repair sheets was also investigated. Finally, the numerical solution was qualitatively and quantitatively validated using the available experimental results.
Development and validation of an efficient direct numerical optimisation approach for aerofoil shape design
Authors: Khurana M. , Winarto H. 
Published: February 2016

AbstractIntelligent shape optimisation architecture is developed, validated and applied in the design of high-altitude long endurance aerofoil (HALE). The direct numeric optimisation (DNO) approach integrating a geometrical shape parameterisation model coupled to a validated flow solver and a population based search algorithm are applied in the design process. The merit of the DNO methodology is measured by computational time efficiency and feasibility of the optimal solution. Gradient based optimisers are not suitable for multi-modal solution topologies. Thus, a novel particle swarm optimiser with adaptive mutation (AM-PSO) is developed. The effect of applying the PARSEC and a modified variant of the original function, as a shape parameterisation model on the global optimal is verified. Optimisation efficiency is addressed by mapping the solution topology for HALE aerofoil designs and by computing the sensitivity of aerofoil shape variables on the objective function. Variables with minimal influence are identified and eliminated from shape optimisation simulations. Variable elimination has a negligible effect on the aerodynamics of the global optima, with a significant reduction in design iterations to convergence. A novel data-mining technique is further applied to verify the accuracy of the AM-PSO solutions. The post-processing analysis, to swarm optimisation solutions, indicates a hybrid optimisation methodology with the integration of global and local gradient based search methods, yields a true optima. The findings are consistent for single and multi-point designs.
Effects of pitching rotation on aerodynamics of tandem flapping wing sections of a hovering dragonfly
Authors: Elarbi E. M. , Qin N. 
Published: February 2016

AbstractThis paper studies hovering capability of flapping two-dimensional tandem wing sections inspired by a real dragonfly wing configuration and kinematics. Based on unsteady numerical simulations, the dragonfly corrugated wings have been benchmarked against a flat wing in terms of the aerodynamic forces and flow structures generated during a flapping cycle. The timing of rotation at each stroke is studied by pitch rotation at three different rates, i.e., 80%, 60% and 40% of a flapping period. The results suggest that the longer time pitch rotation with the period of 80% of the overall flapping period is closer to the force calculations obtained of a balanced flight, that is, the mean vertical force supports the dragonfly weight of 0.754 g with a small difference of 0.92% and the mean horizontal force indicates negligible thrust. However, the corrugated wing performs aerodynamically differently from the flat plate with differences in and in by ±2.06% for the corrugated shape. The vorticity flow field for both wings have been recorded at some instants of flapping motions which give more explanation of such dissimilarity.
Adaptive moving average for trending of accident rates
Authors: Merens M. 
Published: February 2016

AbstractThe yearly accident rate is a common metric used to measure aviation safety performance on a yearly and global basis. This technical note establishes the algorithm for an adaptive moving average which can be used to trend accident rates or any other event counting type of safety indicators. The algorithm was built around the concept of Bollinger Bands and allows easy detection of significant increases or decreases of the accident rate.
Optimisation of RNAV noise and emission abatement standard instrument departures
Authors: Hartjes S. , Visser H. G. , Hebly S. J. 
Published: February 2016

AbstractIn an effort to reduce the negative impact of civil aviation on the human environment, trajectory optimisation techniques have been used to minimise the single event impact of noise and gaseous emissions of departures on communities in the vicinity of airports. For this purpose, the earlier developed trajectory optimisation tool NOISHHH has been adapted to design departure trajectories optimised for environmental criteria, based on area navigation. The new version of NOISHHH combines a noise model, an emissions inventory model, a geographic information system and a dynamic trajectory optimisation algorithm to generate flight paths with minimised environmental impact. Operational constraints have been introduced to ensure that the resulting flight paths are fully compliant with the guidelines and regulations that apply to the design of standard instrument departures and the use of area navigation. To illustrate the capabilities of the new version of NOISHHH, two numerical examples are presented, which are both redesigns of standard instrument departures currently in use at Amsterdam Airport Schiphol.
Computational and experimental study of intake ground vortices
Authors: Zantopp S. , MacManus D. , Murphy J. 
Published: February 2016

AbstractThe ground vortices generated by an intake under both headwind and crosswind configurations have been investigated using computational and experimental approaches. The flow field of a scale-model intake was experimentally studied using stereoscopic particle image velocimetry to measure the ground vortex in conjunction with induct total pressure measurements for the internal flow. The computational predictions were performed using an unsteady Reynolds averaged Navier-Stokes approach. The experimental results show that under crosswind conditions a single ground vortex forms which becomes stronger as the crossflow velocity is increased. Under headwind conditions the measured ground vortex strength initially increases with freestream velocity before it reaches a local maximum and then reduces thereafter. The computations also exhibit the same characteristics and show good agreement with the measurements for some configurations. Based on the predictions, the complex flow field topology is investigated and a detailed flow model of the vortex flow field under crosswind conditions is proposed.
Design of fixed wing micro air vehicles
Authors: Cosyn P. , Vierendeels J. 
Published: February 2016

AbstractThe paper describes the methodology and computational design strategies used to develop a series of fixed wing micro air vehicles (MAVs) at the Ghent University. The emphasis of the research is to find an optimal MAV-platform that is bound to geometrical constraints but superior in its performance. This requires a multidisciplinary design optimisation but the challenges are mainly of aerodynamic nature. Key areas are endurance, stability, controllability, manoeuvrability and component integration. The highly three-dimensional low Reynolds number flow, the lack of experimental databases and analytical or empirical models of MAV-aerodynamics required fundamental research of the phenomena. This includes the use of a vortex lattice method, three-dimensional CFD-computations and a numerical propeller optimisation method to derive the forces and their derivatives of the MAV and propeller for performance and stability-related optimisation studies. The design method leads to a simple, stable and robust flying wing MAV-platform that has the agility of a fighter airplane. A prototype, the UGMAV25, was constructed and flight tests were performed. The capabilities of the MAV were tested in a series of successful flight manoeuvres. The UGMAV15, a MAV with a span of 15cm, is also developed to test flight-qualities and endurance at this small scale. With the current battery technology, a flight-time of at least one hour is expected.
Addressing pose estimation issues for machine vision based UAV autonomous serial refuelling
Authors: Campa G. , Napolitano M. R. , Perhinschi M. , Fravolini M. L. , Pollini L. , Mammarella M. 
Published: February 2016

AbstractThis paper describes the results of an effort on the analysis of the performance of specific ‘pose estimation’ algorithms within a Machine Vision-based approach for the problem of aerial refuelling for unmanned aerial vehicles. The approach assumes the availability of a camera on the unmanned aircraft for acquiring images of the refuelling tanker; also, it assumes that a number of active or passive light sources – the ‘markers’ – are installed at specific known locations on the tanker. A sequence of machine vision algorithms on the on-board computer of the unmanned aircraft is tasked with the processing of the images of the tanker. Specifically, detection and labeling algorithms are used to detect and identify the markers and a ‘pose estimation’ algorithm is used to estimate the relative position and orientation between the two aircraft.Detailed closed-loop simulation studies have been performed to compare the performance of two ‘pose estimation’ algorithms within a simulation environment that was specifically developed for the study of aerial refuelling problems. Special emphasis is placed on the analysis of the required computational effort as well as on the accuracy and the error propagation characteristics of the two methods. The general trade offs involved in the selection of the pose estimation algorithm are discussed. Finally, simulation results are presented and analysed.
Towards a full two dimensional gas turbine performance simulator
Authors: Pachidis V. , Pilidis P. , Marinai L. , Templalexis I. 
Published: February 2016

AbstractIn commercially available gas turbine performance simulation tools, individual engine components are typically represented with non-dimensional maps of experimental or default data. In those cases where actual component characteristics are not available and default characteristics are used instead, conventional tools can deviate substantially at off-design and transient conditions. Similarly, when real component characteristics are available, conventional engine cycle simulation tools can not predict the performance of the engine at other than nominal conditions satisfactorily, or account for the impact of changes in component geometry.This study looked into the full integration of two-dimensional streamline curvature component models with a low fidelity cycle program. Firstly, the obtained engine performance was compared against the one calculated based on default component characteristics. As a second case study, a range of flight Mach numbers and angles of attack were examined together with the effect of three different intake lip geometries on the performance of a notional, two-spool, low-bypass ratio, military engine. Two-dimensional models were used in the engine cycle analysis to provide a more accurate, physics- and geometry-based estimate of intake and fan performances.The analysis carried out by this study demonstrated relative changes in the predicted engine performance larger than 1%. For briefness, representative results are presented and discussed in this paper for one flight Mach number and angle of attack setting. More importantly, this research effort established the necessary methodology and technology required towards a full, two-dimensional engine cycle analysis at an affordable computational resource in the very short term.
Performance characterisation of MPD thrusters
Authors: Nada T. R. 
Published: February 2016

AbstractThis paper introduces a characterisation of the performance indices and operating limits of the self field magnetoplasmadynamic thruster. The thrust, specific impulse, and efficiency are considered as the main performance indices, while the operating limits are the cathode lifetime, onset phenomenon, and the overfed state of the thruster. The effects of thruster parameters (current, mass flow rate, geometry, and propellant type) on the performance indices and operating limits are examined using one-dimensional model of cylindrical self-field thrusters. Design charts are presented to help the designers to choose the optimum and safe set of the thruster parameters that realise certain mission requirements.
Dynamic gain scheduled control of a Hawk scale model
Authors: Richardson T. , Lowenberg M. , Jones C. , Dubs A. 
Published: February 2016

AbstractWhen designing flight control laws using linearisations of an aircraft model about different flight conditions, some form of scheduling of the resultant gains will often be required to implement the controller over wide operating regions. In practice, the controller gains are often scheduled against relatively slowly-varying system states such as altitude or velocity. However, it may also be desirable to schedule gains against rapidly-varying states such as angle-of-attack, thereby generating a cyclic dependence through hidden coupling terms. Previous published work at Bristol has developed a numerical method of accounting for this dependence when scheduling state feedback gains against coupled states. The resulting ‘dynamic gain schedule’ is shown to significantly improve the transient response of the aircraft model during rapid manoeuvring and to reduce the chances of control surface actuator position limit saturation. In this paper, the novel design process, using eigenstructure assignment, is applied to a mathematical second-order longitudinal aircraft model which represents an approximate BAe Hawk wind-tunnel model. The dynamic gain scheduled controller is shown to work extremely well in practice when applied to the closed-loop experimental rig. Despite the highly nonlinear characteristics of the model aerodynamics and tailplane actuation system, as well as unmodelled high turbulence levels, dynamic gain scheduling demonstrates stable closed loop control even in regions where the nonlinearities are such that conventional gain scheduling fails to produce a stable response.
A PIV investigation of the characteristics of micro-scale synthetic jets
Authors: Guo F. , Zhong S. 
Published: February 2016

AbstractAlthough macro-scale synthetic jets are well studied, our knowledge of the behaviour of micro-scale synthetic jets is still extremely limited due to the difficulty in performing detailed measurements with a desirable spatial solution. In the work presented in this paper, a PIV study of the characteristics of synthetic jets issued into quiescent air from orifices of 5mm and 0·5mm diameter respectively is undertaken. It is found that the vortex rollup is much weaker for the 0·5mm jets due to their low Stokes number which results in a near parabolic exit velocity profile. To ensure an appreciable vortex rollup that is desirable for effective flow control, the actuator has to be operated at much higher frequencies to ensure that the Stokes number is greater than a certain threshold value. Furthermore the study shows that the characteristics of synthetic jets of different scales are identical when the dimensionless stroke length (L), Stokes number (S) and Reynolds number (ReL) are the same. On the basis of these scaling parameters, the finding acquired from the studies on macro-scale actuators can be applicable to micro-scale actuators, which are more difficult to measure. Finally, it is also found that although the linear relationships between (L and ReL) and actuator operating conditions observed for macro-scale synthetic jets are no longer valid for micro-scale synthetic jets, the linear relationships between the dimensionless jet performance parameters and (L and ReL) still exist for micro-scale synthetic jets.
Linear and Non-Linear Turbulence Model Predictions of Vortical Flows in Lobed Mixers
Authors: Salman H. , Jiang D. , Page G.J. , McGuirk J.J. 
Published: February 2016

AbstractLobed mixers are widely used in gas turbine engines to increase mixing between hot and cold streams and consequently reduce jet noise. CFD predictions are presented for a simplified experimental configuration of a planar, three lobe geometry. Results are shown for a standard lineark–ε turbulence model, the same model with a time scale limitation invoked and a non-linear quadratic model also employing a time scale limitation. Comparisons are presented between the three models for axial velocity, velocity vectors, shear stress and turbulence kinetic energy at a selected plane in the mixing region. The non-linear model was found to have little influence on the mean flow but some effect on the turbulence structure was observed. Comparison with measurements showed that all major features were reproduced but detail differences were evident. The use of a time scale limit reduced peak values of predicted turbulence quantities by 20-30%. As compared to the standard linear model, the time scale limited non-linear model moved the position of the zero streamwise circulation location by about one lobe wavelength upstream so giving better agreement with experiment.
The longitudinal flying qualities of a blended-wing-body civil transport aircraft
Authors: Cook M. V. , de Castro H. V. 
Published: February 2016

AbstractThis paper describes an evaluation of the longitudinal flying qualities of a generic blended-wing-body (BWB) transport aircraft at low speed flight conditions. Aerodynamic data was obtained from several sources and integrated into the equations of motion of a typical BWB configuration in order to provide a reasonable basis for flying qualities assessment. The control requirements to trim are enumerated for a representative range of cg position and static margin over the typical range of approach speeds for both stable and unstable configurations. The linear dynamic characteristics of the unaugmented airframe are also described for the same range of stability margin. Subsequent work describes the development of a rate command-attitude hold command and stability augmentation system configured to comply with representative modern handling criteria. Finally, the flight dynamics of the augmented aircraft are described after refinement of the control law by means of piloted simulation in a fixed base flight simulator.
Closed-loop flutter control using strain actuation
Authors: Kandagal S. B. , Venkatraman K. 
Published: February 2016

AbstractThe present work investigates feedback control of flutter using piezoceramic strain actuators. A two degree-of-freedom oscillating airfoil model with the air loads simulated assuming unsteady aerodynamics is considered. Various feedback measurement combinations for SISO feedback control and strain actuation in the heave and pitch direction are studied to quantify their effect on flutter. The effect of sensor placement on the airfoil, for combined pitch and heave measurement feedback, is also studied. The results show that for a given aeroelastic system, sensor location is an important parameter in realizing an increase in the flutter speed. It is demonstrated that the flutter speed can be increased by more than 50% through strain actuation in the pitch direction.
State-space inflow modelling for lifting rotors with mass injection
Authors: Yu K. , Peters D. A. 
Published: February 2016

AbstractIn the field of rotorcraft dynamics, it is significant that the induced inflow field is well understood and modeled. A large number of methodologies have been developed in the past years, among which the state-space model is recognised for its advantage in real-time simulation, preliminary design, and dynamic eigenvalue analysis. Recent studies have shown success in representing the induced flow field everywhere above the rotor plane even with mass source terms on the disk as long as they have zero net flux of mass injection when integrated over the disk. Nevertheless, non-zero net mass influx is expected in numerous situations, such as ground effect, tip drive rotors, etc; and the incapability of previous models limits the utilisation of the methodology in these cases. This work presents an extended potential-flow, state-space model derived from the potential-flow momentum equation by means of a Galerkin approach. The induced velocity and pressure perturbation are expanded in terms of closed-form, time-dependent coefficients and space-dependent associated Legendre functions and harmonics. Non-zero net mass flux terms are represented by the involvement of associated Legendre functions with equal degrees and orders. Validation, as well as discrepancies, of the inclusion of such terms is investigated. Numerical simulation of frequency response in axial and skew-angle flight is presented and compared with exact solutions obtained by the convolution integral. Also the study shows that, unlike other pressure distribution responses, non-zero mass influx exhibits a high sensitivity to the choice of the number of states in the velocity expansion. Error analyses are performed to show this sensitivity.