bluuebunny/crossref_metadata_2025_split huggingface dataset:
‘Smart spring’ identification for hovering rotor aeroelastic-stability augmentation
Authors: Gennaretti M. , Poloni L. , Nitzsche F. 
Published: July 2022

AbstractThis work deals with tailoring of adaptive material included at the roots of hingeless helicopter rotor blades to be used in individual blade control (IBC) strategies.Usually, IBC strategies involving the use of adaptive materials either consider adaptive material embedded in the blade structure for inducing strain deformations, or apply adaptive actuators for controlling segments of the blade (e.g. for moving trailing-edge flaps).Here, the adaptive material is used to provide augmentation of modal damping in a passive control approach, that can be conveniently tuned so as to make it the most suitable for the actual rotor configuration under examination. The presentation of a procedure for tailoring this ‘smart spring’ is the aim of the paper.The aeroelastic blade model considered consists of a cantilever slender beam undergoing flap, lead-lag and torsional motion, coupled with a strip theory approach for the prediction of the aerodynamic loads, based on the very low frequency approximation of the pulsating-free-stream Greenberg’s theory.Starting from this model and applying the Galërkin method, generalised mass, damping and stiffness matrices of the basic blade, as well as the incremental generalised mass, damping and stiffness matrices due to the ‘smart spring’ have been determined, the latter depending on the ‘smart spring’ inertial and elastic characteristics.It will be shown that the application of an optimal control criterion, followed by a low frequency-approximation observer, yields the identification of the most suitable ‘smart spring’ characteristics for augmentation of rotor blade aeroelastic stability. The validity of this procedure will be demonstrated by numerical results concerning the stability analysis of two hovering blade configurations.
Low cost Mercury orbiter and sample return missions using solar sail propulsion
Authors: McInnes C. R. , Hughes G. , McDonald M. 
Published: July 2022

AbstractThe use of solar sail propulsion is investigated for both Mercury orbiter (MO) and Mercury sample return missions (MeSR). It will be demonstrated that solar sail propulsion can significantly reduce launch mass and enhance payload mass fractions for MO missions, while MeSR missions are enabled, again with a relatively low launch mass. Previous investigations of MeSR type missions using solar electric propulsion have identified a requirement for an Ariane V launcher to deliver a lander and sample return vehicle. The analysis presented in this paper demonstrates that, in principle, a MeSR mission can be enabled using a single Soyuz-Fregat launch vehicle, leading to significant reductions in launch mass and mission costs. Similarly, it will be demonstrated that the full payload of the ESA Bepi Colombo orbiter mission can be delivered to Mercury using a Soyuz-Fregat launch vehicle, rather than Ariane V, again leading to a reduction in mission costs.
A numerical study of hypersonic laminar film cooling
Authors: Yang X. , Badcock K. J. , Richards B. E. 
Published: July 2022

AbstractA computational study has been performed to investigate the effectiveness of film cooling in hypersonic laminar flows. Both the primary and the coolant flow are air. First, three different primary flow conditions are used for validation. A uniform boundary condition at the slot exit is found to give unrealistic predictions of the heat transfer rate, whilst a boundary condition involving extended coolant inlet gives improvement. Then five coolant injection rates and three slot heights are examined. It is confirmed that increasing the coolant injection rate can increase the film cooling effectiveness for laminar cases. But slot height does not play an important role under the flow conditions in this study. The computational results are compared with the experimental results and good agreement is achieved.
Flight simulation in academia HELIFLIGHT in its first year of operation at the University of Liverpool
Authors: Padfield G. D. , White M. D. 
Published: July 2022

AbstractThe challenges of helicopter simulation are being tackled across a broad front as technology is developed to meet the needs of Industry. Traditionally, the strongest impetus has come from the training community and this is likely to continue for some time as simulation technology advances at increasing pace, raising fidelity standards. The development of PC-based simulation technologies is providing a significant spur in this development and lowering the cost, making complete simulation systems of reasonably high fidelity available to smaller organisations. This paper describes the first year of operation with such a system at the University of Liverpool – HELIFLIGHT. With its full motion, wide field-of-view visuals, programmable force-feel system and the comprehensive FLIGHTLAB modelling environment, we describe the HELIFLIGHT system as high fidelity and the first year of utilisation saw extensive use in a variety of handling qualities and pilot-vehicle technology research and teaching. Some of these are described in the paper and from a year of many highlights, the EU-funded programme to develop handling qualities for a civil tilt rotor aircraft is selected to demonstrate the versatility of the HELIFLIGHT system.
Curve fitting approach for transonic flutter prediction
Authors: Sedaghat A. , Cooper J. E. , Wright J. R. , Leung A. Y. T. 
Published: July 2022

AbstractThis paper outlines an initial investigation for determining nonlinear aerodynamics for unsteady transonic flows through the use of curve fitting unsteady computational fluid dynamics (CFD) data. The full aerodynamics including linear and non-linear aerodynamics can be identified as a polynomial function. Through the curve fitting method, the important non-linear terms can be identified and the smaller terms can be neglected. Having modelled the non-linear aerodynamics and included into the aeroelastic model, the characteristics and stability of non-linear aeroelastic system can then be investigated using normal form theory. The methodology is demonstrated upon a simple two-degrees-of-freedom aeroelastic wing model with structural and aerodynamics nonlinearity. A good agreement is obtained for all cases studied between analytical and simulation results.
Numerical investigation of staged transverse sonic injection in Mach 2 stream in confined environment
Authors: Chakraborty D. , Roychowdhury A. P , Ashok V. , Kumar P. 
Published: July 2022

AbstractTransverse sonic injection, usually in a staged manner, in a confined environment is a necessity in the design of an efficient combustion chamber. The design requires an analysis of the mixing of the injectant with incoming stream as efficient combustion depends upon good mixing. This kind of analysis needs numerical model/simulation to assess the mixing of the two streams. To determine the suitability of an existing software package for such a study, staged transverse sonic injection into a Mach 2 stream in a confined environment is taken as a test case. The experimental conditions of McDaniel et al are reproduced for this simulation. In this experiment, staged transverse injection of sonic jet behind the backward facing step in Mach 2 stream was carried out and profiles of various flow parameters were measured. The numerical simulation solves the 3D Navier-Stokes equations with a k – ε turbulence model using the PARallel Aerodynamic Simulator PARAS3D. Computed results show a good match for injectant penetration profile although the computations predict slightly higher penetration near the orifice location. Detailed comparison of flow parameter profiles between computed and experimental data reveal that in the zone away from the injection orifice, computations predict the flow field reasonable well. However, in the vicinity of the orifice, there are some differences between experimental data and computed results. These differences could be due to non-uniform inlet profile in the experiment and/or inadequacy of the turbulence model considered in the study.
An investigation into the longitudinal dynamics and control of a flapping wing micro air vehicle at hovering flight
Authors: Loh K. , Cook M. , Thomasson P. 
Published: July 2022

AbstractThis paper describes the research into the flight dynamics modelling and flight control of a flapping wing micro aerial vehicle (MAV). The equations of motion based on a multi-body representation of the vehicle and the flapping wings were derived and form the basis for the simulation program, which was developed using MATLAB and SIMULINK. The aerodynamic forces were obtained through experimental methods and form the basis for the aerodynamic model.The hovering and low speed flight of the MAV was investigated using a SIMULINK simulation model. Various flight control concepts, inspired by observation of insect and bird flight, were investigated in some detail. The concepts include the control of flap frequency, flap and pitch phasing (wing beat kinematics) and shift in centre of gravity position. The paper concludes with a comparison of the control concepts and their feasibility for a practical vehicle application.
Reduction of helicopter vibration through cyclic control of variable orifice dampers
Authors: Anusonti-Inthra P. , Gandhi F. , Miller L. 
Published: July 2022

AbstractThe present study demonstrates that cyclically varying the damping coefficient of controllable lag and flap dampers can reduce the 4/revvibratory hub loads of a four-bladed hingeless rotor helicopter in high speed forward flight. Gradient-based optimization is used to determine the optimal multi-cyclic damping variation inputs that minimise a composite vibration index comprising of all six components of vibratory hub loads. Optimal 2/rev and 3/rev variations in the lag damping coefficient virtually eliminate the vibratory hub drag force and yawing moments, and produce small reductions in the vibratory hub side force. The optimal lag damping variations, interestingly, produce increases in the 3/rev and 5/rev components of the blade root drag shear, that cancel the contributions of the blade root radial shear to the vibratory in-plane hub forces. Despite some increases in higher harmonics of blade response, damper loads, and blade and flexbeam root loads, the lower harmonics and the peak-to-peak values show little change, implying that blade and damper fatigue life would not be adversely affected. When optimal 2/rev and 3/rev variations in flap damping coefficient are introduced in conjunction with the optimal lag damping variations, 30% reductions in the hub vertical vibrations are obtained, in addition to the previous reductions in the vibratory in-plane forces and yawing moment. The cyclic flap damping variations reduce the higher harmonics of the blade root vertical shear. Reductions in hub vibration levels are obtained over a range of forward flight speeds.
Non-linearities in flight control systems
Authors: Fielding C. , Flux P. K. 
Published: July 2022

AbstractNon-linear behaviour is usually undesirable for the operation of any system and it needs to be minimised in flight control systems in order to provide the pilot with a predictable and well-behaved aircraft. The non-linear response characteristics exhibited by all aircraft and their flight control systems can be characterised by using nonlinear functions to simulate and analyse their behaviour. This paper explores the types of physical non-linearities that exist in aircraft flight control systems and provides some examples. It describes how the non-linear stability might be analysed and addresses the subject of actuation systems modelling. The final section provides recommendations for minimising non-linear behaviour and gives some general guidelines on how to deal with non-linear characteristics.
Flocking of autonomous unmanned air vehicles
Authors: Crowther B. 
Published: July 2022

AbstractThe use of large numbers of unmanned air vehicles in a given air space presents a challenge for conventional air traffic control methods. Flocking (or schooling, swarming or herding) in nature arises when mobile organisms find benefit in living at high densities. The present paper applies rules of flocking (cohesion, alignment, separation, and migration) to the problem of managing the flight of a number of autonomous unmanned air vehicles. A six-degree of freedom aerodynamic model of an existing UAV is used to simulate the flocking flight vehicles. It is found that application of the cohesion and alignment rules is sufficient to generate true flocking behaviour in that the flight vehicle density is increased and the flock members converge on a common heading. Increasing rule strength reduces the time taken to achieve flocking behaviour. However increasing rule strength too far leads to oscillatory or unstable flight paths. It is found that flock behaviour can be adequately described using the time histories of two statistical parameters: the mean radius between flock members and the standard deviation of the flock members’ heading angles.
A flight test to demonstrate flutter and evaluate the flutterometer
Authors: Lind R. , Voracek D. F. , Truax R. , Doyle T. , Potter S. , Brenner M. 
Published: July 2022

AbstractA project was recently completed that investigated the ability to predict the onset of flutter using tools like the flutterometer. This project used an experiment called the aerostructures test wing that was flown while mounted to the flight test fixture on an F-15. Several flight tests were conducted to expand the envelope and determine the aeroelastic dynamics of the experiment. The final flight ended with destruction of the experiment due to the onset of flutter. The flutterometer attempted to predict this onset by analysing the flight data. The results indicate the flutterometer is able to generate a conservative estimate of the flight conditions associated with flutter. This paper details the flight tests of the experiment and the resulting predictions from the flutterometer.
A dynamically fuzzy gain – scheduled design for missile autopilot
Authors: Lin Chun-Liang , Hwang Chai-Lin 
Published: July 2022

AbstractA dynamic backpropagation training algorithm for an adaptive fuzzy gain scheduling feedback control scheme with the application to missile autopilots is developed. This novel design methodology uses a Takagi-Sugeno fuzzy system to represent the fuzzy relationship between the scheduling variables and controller parameters. Mach number and angle-of-attack are used as measured, time-varying exogenous scheduling variables injected into the control law. By incorporating scheduling parameter variation information, the adaptation law for controller parameters is derived. Results from extensive simulation studies show that the presented approach offers satisfactory controlled system performance.
Optimisation of noise abatement arrival trajectories
Authors: Visser H. G. , Wijnen R. A. A. 
Published: July 2022

AbstractThis paper describes an optimisation study concerning arrival trajectories that has been conducted using a recently developed tool for the analysis and design of noise abatement procedures around airports. This new tool combines a noise model, a geographic information system, and a dynamic trajectory optimisation algorithm. The optimisation algorithm generates routings and flight-paths that minimise the noise impact in the residential communities surrounding the airport, while satisfying all imposed operational and safety constraints. The study on arrival trajectories presented herein complements an earlier study involving departure trajectories. Although the numerical results shown pertain to a particular example airport, viz Amsterdam Airport Schiphol, the study actually focuses on the development of a generic methodology that could be applied to any given airport. The results clearly demonstrate the effectiveness and flexibility of the developed tool.
Design aspects of the adaptive wing — the elastic trailing edge and the local spoiler bump
Authors: Monner H. P. , Breitbach E. , Bein Th. , Hanselka H. 
Published: July 2022

AbstractMarket research predicts a large growth in numbers of passengers as well as airfreight volume for the aircraft industry. An expected concomitant increase in competition for the European aircraft industry demands that the efficiency of new aircraft has to be drastically improved. One approach to achieve this is the aerodynamic optimisation of the wing. The fixed wing is designed optimally only for one flight condition. This flight condition is described by the parameters altitude, Mach number and aircraft weight which vary continuously during the mission of the aircraft. Therefore, the aircraft is just periodically near the chosen design point. To compensate for this major disadvantage, an adaptive wing for optimal adaptation and variation of the profile geometry to the actual flight conditions is under development. DaimlerChrysler Aerospace Airbus, DaimlerChrysler Research and the German Aerospace Centre (DLR) are working as project partners on concepts for a variable camber and a local spoiler bump. In this paper structural concepts developed by the German Aerospace Centre for both objectives will be presented. The concepts are designed under the aspect of adaptive structural systems and require a high integration of actuators, sensors and controllers in the structure. Special aspects of the design will be discussed and first results, analytical, numerical as well as experimental, will be presented. Part of the concept design is also the development of new actuators optimised for the specific problem. A new actuator concept for the spoiler bump based on a cylindrical tube and activated either by pressure or multifunctional materials (e.g. shape memory alloys) will additionally be shown.
A new approach to the third order calibration of internal strain gauge balances used for aerodynamic load measurement
Authors: Niven A. J. , Tait S. W. 
Published: July 2022

Abstract
With respect to wind tunnel aerodynamic load measurement, an internal strain gauge balance (often referred to as a sting balance) is essentially a compact load cell designed to fit within a cavity of the aerodynamic body and form a link between the model and a fixed ground point via a sting support system. The structure of an internal strain gauge balance is designed to incorporate a series of planar surfaces such that the deflection of each surface is predominantly induced by a unique aerodynamic load. Strain gauges, mounted on groups of surfaces in a Wheatstone bridge arrangement produce output signals proportional to the applied aerodynamic loads. A strain gauge balance is calibrated by applying known loads, measuring the bridge outputs and then formulating an equation which relates the two variables together. Although calibration techniques are well established, reservations have been recently expressed concerning the ability of the associated calibration equation to satisfactorily model the response of the balance when subjected to a six component aerodynamic loading. This generally accepted calibration equation (referred to here as the traditional equation) results in a quadratic approximation to the behaviour of the output signals with applied loads, whereas a more appropriate variation would be cubic. Other limitations of the traditional calibration equation are that the behaviour of the balance to two simultaneously applied loads is based upon limited combinations of the two applied loads, and that the acquisition of the required loads from the strain gauge signals is frequently based upon an approximate matrix inversion method. The proposed calibration equation, described within this paper, models the behaviour of the sting balance to the third order, takes account of all possible combinations of two simultaneously applied loads, and avoids the use of an approximate matrix inversion when deriving the desired aerodynamic loading from the signal outputs. It is also shown that the proposed method may be used to determine the interaction of all possible combinations of up to three simultaneously applied loads.
Experimental audit of the mixing-plane approach to turbomachinery analysis and a review of alternative multi-row techniques
Authors: Lockwood C. , Ivey P. C. , R. G. Wells  
Published: July 2022

AbstractDetailed numerical comparisons of pressure and flow angle measurements made in stage three of a four-stage, large scale, low speed, axial compressor are presented. The measurements are in both the rotating and stationary frame and were obtained as part of a BRITE/EURAM collaborative study of cantilevered and shrouded-stator compressor configurations. The numerical analysis is 3D, considers three blade rows simultaneously and incorporates multiple row effects by use of a conservative mixing-plane model allowing circumferential variation at the mixing plane.The paper discusses the early results of a study sponsored by Alstom Gas Turbines to examine steady-state, multiple blade-row modelling techniques. Growth in the endwall flow region due to multi-row effects is revealed from both the numerical and experimental results. The numerical simulation is conducted without altering blade gap spacings to assist numerical stability; the axial gap is increasingly being seen as a critical performance parameter for multiple row analysis. The limitations inherent in an approach using mixing-planes are presented and a review of alternative, more rigourous, treatments of these effects is then discussed. These treatments attempt to retain the unsteady flow structure in a steady-state model by the derivation of so-called deterministic stresses.
The influence of mid-chord battle damage on the aerodynamic characterstics of two-dimensional wings
Authors: Irwin A. J. , Render P. M. 
Published: July 2022

AbstractThis paper briefly considers the method of simulating gunfire damage to a wing and outlines the key basic assumptions used in modelling. The results of qualitative and quantitative investigations into the aerodynamic characteristics of a wing damaged at quarter chord are then presented. The results are discussed in terms of flow mechanisms, changes to surface pressure distributions and increments in lift, drag and pitching moment coefficients. For the damaged wing, the influence on force and moment coefficients was attributed to flow through the damage. This through flow was driven by the pressure differential between the upper and lower wing surfaces, and took one of two forms. The first form was a ‘weak-jet’ which formed an attached wake and resulted in small changes in force and moment coefficients. The second form resulted from either increased incidence, or damage size. This was the ‘strong-jet’, where through flow penetrated into the freestream flow, resulting in separation of the oncoming surface flow, and the development of a larger separated wake with reverse flow. The effect on force and moment coefficients was significant. The paper also compares the structure of the damage through flow with previously published results for jets in crossflows. Many similarities in the flow features were identified, although there were significant differences in the surface pressure distributions for the two cases.