bluuebunny/crossref_metadata_2025 huggingface dataset:
A technique for predicting pilot model parameters using inverse simulation
Authors: Leacock G. R. , Thomson D. G.
Published: July 2016

The practice of using mathematical models to simulate pilot behaviour in one–axis stabilisation tasks is a well–known conventional simulation problem. In this paper an accepted mathematical model of a pilot is used as the controller of a rudimentary helicopter model. Flight test manoeuvre data from inverse simulation runs is used to provide time–histories which represent input forcing functions to the pilot–helicopter system, and a constrained optimisation routine is utilised to obtain values for the pilot gain and lead/lag equalisation parameters. It will be shown that as the theoretical pilot is required to ‘fly’ different manoeuvres, or indeed if the level of manoeuvre aggression is varied, the ‘pilot’ adjusts these parameters to perform a tracking task in compensatory control. The paper considers initially the pilot and helicopter models and subsequently analyses the whole system, illustrating how the pilot model changes with different situations.
Laplace-domain approximation to the transfer functions of a rotor blade in forward flight
Authors: F. Nitzsche
Published: July 2016

A continuous frequency domain method with roots on the classic Hill’s determinant analysis is presented to approximate the time-varying characteristics of a linear periodic system. The method is particularly useful to derive a time-invariant equivalent form of the time-varying aeroelastic problem of a rotor blade in forward flight. The proposed technique allows methodology usually employed in fixed wing aircraft to obtain closed-loop control laws be extended to rotary wings. The method is first validated solving Mathieu’s equation. Next, the two-degree-of-freedom (flap bending and torsion) problem of rotating beam subject to unsteady and incompressible aerodynamics in forward flight is solved in the laplace domain. As a demonstration of the proposed method, the transfer functions in the ‘s’ plane between a sudden and uniformly distributed input pressure perturbation applied along the beam and the output response of the two elastic degrees of freedom considered are obtained at a set of local sections.
The application of self-organising fuzzy control to station-keeping in unmanned air vehicles
Authors: Platts J. T. , Forsythe W.
Published: July 2016

This paper reports on part of a larger study examining the applicability of fuzzy logic to the higher level supervisory control functions of unmanned air vehicles and details the work so far in testing the feasibility of a candidate self-organising scheme. The candidate algorithm consists of a regular fuzzy control system whose rule set is improved over time as a function of the deviation of the plant from some desired performance. Historically, virtually all work in this area has examined the application of the algorithm to the classic regulator problem, and focussed on achieving both better performance in that role and establishing tuning guidelines based on a more systematic approach. The application discussed in this paper is assessing the algorithm to ascertain its possible utility in the higher level supervisory capacities. The candidate control problem was one of station-keeping of one air vehicle behind another.
Extensions to Maskell’s theory for blockage effects on bluff bodies in a closed wind tunnel
Authors: Hackett J. E. , Cooper K. R.
Published: July 2016

Extensions to Maskell’s original correction method, developed over several years, are consolidated and designated ‘Maskell III’. The procedures were applied to dedicated tests on a family of flat-plate wing models in a small, low-speed wind tunnel at NRC. Test conditions included angles of attack from -10° to 110° and models of up to 16% of tunnel area. Off-centre tests were included with model-to-wall distances down to 0.72 chords. Corrected lift and drag data correlated well between models of different sizes and at different offsets from the tunnel centreline. Comparisons are made with corrections using the pressure-signature and two-variable methods, emphasising post-stall conditions. These showed that the ‘Maskell III’ procedures, which require minimal input, correlated as well as the other methods for most model sizes and positions in the tunnel.
A fully distributed unstructured Navier-Stokes solver for large-scale aeroelasticity computations
Authors: Barakos G. , Vahdati M. , Sayma A.I. , Bréard C. , Imregun M.
Published: July 2016

This paper presents the development and validation of a parallel unsteady flow and aeroelasticity code for large-scale numerical models used in turbo machinery applications. The work is based on an existing unstructured Navier-Stokes solver developed over the past ten years by the Aeroelasticity Research Group at Imperial College Vibration University Technology Centre. The single-process multiple-data paradigm was adopted for the parallelisation of the solver and several validation cases were considered. The computational mesh was divided into several sub-sections using a domain decomposition technique. The performance and numerical accuracy of the parallel solver was validated across several computer platforms for various problem sizes. In cases where the solution could be obtained on a single CPU, the serial and parallel versions of the code were found to produce identical results. Studies on up to 32 CPUs showed varying levels of parallelisation efficiency, an almost linear speed-up being obtained in some cases. Finally, an industrial configuration, a 17 blade row turbine with a 47 million point mesh, was discussed to illustrate the potential of the proposed large-scale modelling methodology.
Constant temperature hot-wire measurements in a short duration supersonic wind tunnel
Authors: Weiss J. , Knauss H. , Wagner S. , Kosinov A. D.
Published: July 2016

A constant temperature hot-wire anemometer enabling automatic rapid scanning of the wire overheat was built to perform free stream disturbance measurements in the shock wind tunnel of the Institute for Aerodynamics and Gasdynamics at Stuttgart University. It is shown that such a system brings real advantages in terms of testing time. The change of bridge dynamic behaviour with wire temperature is taken into account by measuring the bridge frequency response with a very fast electrical test and postprocessing the data. The method of operation is validated in a supersonic suck down wind tunnel and a comparison with a commercial constant temperature bridge shows good agreement. Results of free stream disturbance measurements in a short duration supersonic wind tunnel of 120ms testing time are presented.
Simulation of flows within an electrostatic ion thruster for space missions
Authors: Jugroot M. , Harvey J. K.
Published: July 2016

Ion thrusters are well suited for near-Earth and deep space missions because of their exceptionally high specific impulse. Those already flying are also proving to be very reliable. The flow of neutral and charged particles within the different components of these devices is very complex and although they have been studied for several years, little of the detail of their internal operation is properly understood. Numerical simulations of these flows can potentially yield an improved understanding of the physical phenomena involved and in turn this should assist in the optimising of new designs and in achieving higher specific impulses. The external plume, which can potentially cause damage to other spacecraft components such as solar panels, has been the object of some studies but the flow within the internal chambers where many complex phenomena are suspected to occur has been seriously neglected. For this reason the present fully kinetic neutral and charged particle simulations, which take account of the ionisation processes and the applied magnetic field, have been conducted. The studies have been made on one specific electrostatic ion thruster - the T5 model produced by the Space Department at the Defence and Evaluation Research Agency (DERA, Farnborough, UK). Two regions within the thruster have been concentrated on, namely the exit area of the hollow cathode and the main chamber.
Integrated sensor/actuator FDI and reconfigurable control for fault-tolerant flight control system design
Authors: Hajiyevt Ch. M. , Caliskan F.
Published: July 2016

In this paper an approach to fault-tolerant flight control system design based on the integration of sensor/actuator fault detection and isolation (FDI) and reconfigurable control is presented. The effects of the sensor and actuator faults in the innovation process of the Kalman filter are investigated, and a decision approach to isolate the sensor and actuator faults is proposed.

The reconfigurable control algorithm based on the Extended Kalman Filter (EKF) is presented. The control reconfiguration procedure is executed by considering the identified control distribution matrix. In the simulations, the longitudinal dynamics of an aircraft control system are considered, and control reconfiguration is examined. In the paper, the principal block diagram of a fault tolerant aircraft control system is offered.
Implicit method for the time marching analysis of flutter
Authors: Goura G. S. L. , Badcock K. J. , Woodgate M. A. , Richards B. E.
Published: July 2016

This paper evaluates a time marching simulation method for flutter which is based on a solution of the Euler equations and a linear modal structural model. Jameson’s pseudo time method is used for the time stepping, allowing sequencing errors to be avoided without incurring additional computational cost. Transfinite interpolation of displacements is used for grid regeneration and a constant volume transformation for inter-grid interpolation. The flow pseudo steady state is calculated using an unfactored implicit method which features a Krylov subspace solution of an approximately linearised system. The spatial discretisation is made using Osher’s approximate Riemann solver with MUSCL interpolation. The method is evaluated against available results for the AGARD 445.6 wing. This wing, which is made of laminated mahogany, was tested at NASA Langley in the 1960s and has been the standard test case for simulation methods ever since. The structural model in the current work was built in NASTRAN using homogeneous plate elements. The comparisons show good agreement for the prediction of flutter boundaries. The solution method allows larger time steps to be taken than other methods.
The theory of the longitudinal static stability of the hang-glider
Authors: Cook M. V.
Published: July 2016

This paper describes the development of a simple theory of the longitudinal static stability of the hang-glider. The classical theory, as developed for the conventional aeroplane, is modified to accommodate the particular features of the hang-glider. When the appropriate assumptions are made, the theory provides simple insight into the controls fixed and controls free stability and control characteristics of the hang-glider. The validity of the theoretical models is successfully demonstrated by application to a typical fifth generation hang-glider wing for which good quality aerodynamic data were available.
The interaction of a vortex with a boundary layer
Authors: Yeung C.P. , Squire L.C.
Published: July 2016

The three-dimensional vortex/boundary layer interaction of a type which may occur on a high-lift aerofoil has been studied. The experimental configuration simulates the trailing vortex system generated by two differentially-deflected slats which interact with an otherwise two-dimensional boundary layer developed on the wing surface under a nominal zero pressure gradient. The mean and turbulent flowfields are measured by a triple hot-wire system. The measurements show that the trailing vortex system includes the vortex sheets shed from the slats and the single vortex formed at the discontinuity between them. The single vortex moves sideways and interacts with the boundary layer as it develops downstream. During the interaction with the boundary layer, the low momentum, high turbulent-kinetic energy flow carrying negative longitudinal vorticity is entrained from the boundary layer and rolled into the vortex at the line of lateral convergence on the test surface. Likewise, at the line of lateral divergence, the high momentum, low turbulent kinetic energy flow carried by the vortex impinges on the boundary layer, suppressing the turbulent energy level and the growth of the boundary layer.
Experimental pressure evaluation near a sail leading edge under real conditions
Authors: Lombardi G. , A. Tonelli
Published: July 2016

The aerodynamic condition corresponding to the optimum sail trim has been long debated; in the present note this aerodynamic aspect of the sails is studied by means of pressure measurements near the sail leading-edge. By analysing the pressure acting on the leading edge zone it can be evidenced that, when the sail is “optimally” trimmed, it is actually in the aerodynamic condition corresponding to the ideal angle of attack.
The development of a Riemann solver for the steady supersonic Euler equations
Authors: Toro E. F. , Chakraborty A.
Published: July 2016

An improved version (HLLC) of the Harten, Lax, van Leer Riemann solver (HLL) for the steady supersonic Euler equations is presented. Unlike the HLL, the HLLC version admits the presence of the slip line in the structure of the solution. This leads to enhanced resolution of computed slip lines by Godunov type methods. We assess the HLLC solver in the context of the first order Godunov method and the second order weighted average flux method (WAF). It is shown that the improvement embodied in the HLLC solver over the HLL solver is virtually equivalent to incorporating the exact Riemann solver.
Full Potential and Euler solutions for transonic unsteady flow
Authors: Ambrosi D. , Gasparini L. , Vigevano L.
Published: July 2016

A comparison between Full Potential and Euler numerical solutions for 2D transonic unsteady flow is presented. The pros and cons of the potential model are discussed and the main features of both computational methods are summarised. The comparison is done for a Naca 0012 aerofoil oscillating in pitch at a freestream Mach number ranging from 0·755 to 0·825, in order to investigate the limit of application of the potential approximation in an unsteady flow.
Modelling requirements in flight simulation
Authors: Barnes A. G.
Published: July 2016

It would be difficult to exaggerate the impact of models on our lives — in recreation, education, investigation, inspiration, and intuition. The models can be real or abstract, static or dynamic, simple or complex, and scaled in size or time. Their use can be either explicit or implicit. Appreciation of the value of models has been heightened by the availability of desktop computing power. Experts on any topic cannot be interviewed on TV without a personal computer in the background, to reinforce their image.
Airspace design: towards a rigorous specification of conflict complexity based on computational geometry
Authors: Fulton N.L.
Published: July 2016

The degree of complexity and randomness of aircraft tracking which can be safely managed is a fundamental question for a given airspace design. To answer this question and to provide optimum conflict resolution strategies, the nature of conflict needs to be thoroughly understood. This paper reviews traditional conflict models showing how these models may be integrated into a more unified model based on computational geometry. This mathematical approach is being investigated for the specification and management of future airspace, achieving a more solid architectural basis for airspace design. This approach has the potential to significantly reduce the subjectivity when attempting to model controller and pilot workload, an important requirement in future designs.
A theoretical investigation of enhanced lift in the presence of thin aerofoil stall
Authors: Yeung W. W. H. , Parkinson G. V.
Published: July 2016

A theoretical study is presented for the investigation of a potential-flow model for enhancing lift over a flat-plate aerofoil experiencing thin aerofoil stall. Rather than suppressing the leading-edge separation, flow is assumed to separate tangentially at the leading edge and made to reattach smoothly at the tip of a forward-facing fence joining the plate tangentially on its upper surface to avoid any unnecessary stagnated flow. The length of the fence and its location from the leading edge form two geometrical parameters. At any positive angle of attack, the resulting bounding streamline emanating from the leading edge and terminating at the tip of the fence is simulated by using suitable mathematical singularities subject to boundary conditions such as attaining a finite velocity at each critical point of the conformal mapping involved, and the condition of finite pressure gradient at reattachment, when applicable. Computational results from varying these two geometrical parameters indicate that the lift from each model is enhanced, as compared with the attached flow model around a simple flat plate and the original separated flow model by Kirchhoff.
Limit cycle oscillation control and suppression
Authors: Dimitriadis G. , Cooper J. E.
Published: July 2016

The prediction and characterisation of the limit cycle oscillation (LCO) behaviour of non-linear aeroelastic systems has become of great interest recently. However, much of this work has concentrated on determining the existence of LCOs. This paper concentrates on LCO stability. By considering the energy present in different limit cycles, and also using the harmonic balance method, it is shown how the stability of limit cycles can be determined. The analysis is then extended to show that limit cycles can be controlled, or even suppressed, by the use of suitable excitation signals. A basic control scheme is developed to achieve this, and is demonstrated on a simple simulated non-linear aeroelastic system.
Incipient separation on flared bodies at hypersonic speeds
Authors: Kontis K. , Stollery J. L.
Published: July 2016

The aerodynamic effectiveness of a cylinder-flare body at zero incidence under laminar and turbulent boundary-layer conditions has been studied experimentally. Two nose geometries, namely a 10° half-angle sharp cone and a hemisphere, were used. The study has been carried out in a hypersonic gun tunnel at a Mach number of 8·2 and a Reynolds number of 158,100, based on the cylinder diameter, at flare angles 0°, 10°, 20°, 30° and 45°. The surface flow was studied using oil-dot and liquid crystal techniques. Some information regarding the shock layer was obtained from schlieren pictures. The effects of entropy layer and boundary-layer state on flare effectiveness were deduced from pressure measurements over the cylinder and the flare.
A comparative study on different techniques to control rotary wing vibration using smart structures
Authors: Nitzsche F.
Published: July 2016

This investigation discusses some proposed techniques to attenuate rotary wing vibration using smart materials. Advantages and disadvantages of these solutions are analysed in greater detail. Numerical results from feasibility studies are summarised to present the accomplishments already achieved and the goals to be pursued in the near future to develop the next generation of the so-called ‘smart rotors’.
Scaling of incipient separation in high
speed laminar flows
Authors: Inger G. R.
Published: July 2016

This study provides the theoretical foundation for a
well-established, but.heretofore empirical,
criterion for incipient separation in moderately
hypersonic shock/boundary layer interactions. It is
based on an examination of the leading high Reynolds
number approximation to triple deck theory, combined
with its reformulation in terms of the reference
temperature concept. The analysis further provides
extensions giving the effects of both low supersonic
Mach numbers and non-adiabatic wall temperatures on
incipient separation.
A cavitating aerofoil with a Prandtl-Batchelor eddy
Authors: Zachariou E. , Wilmott P. , Fitt A. D.
Published: July 2016

A simple model is presented for an aerofoil with a recirculating Prandtl-Batchelor region behind a spoiler. Using thin aerofoil theory the model is posed as a pair of coupled nonlinear singular integrodifferential equations for the shape of the separating streamline and the distribution of vorticity along the aerofoil. These equations are solved numerically and results are presented. In particular, some conclusions are drawn regarding the lift on such aerofoils.
Human flapping-wing flight under reduced gravity
Authors: Collins P.Q. , Graham J.M.R.
Published: July 2016

Recent experiments have demonstrated that humans can fly, with great exertion of the leg muscles using fixed wings and a propeller. However, understanding of aerodynamics and physiology show that using existing technology it is not possible for humans to fly on Earth using their arm muscles to flap wings like birds. Human flapping flight might, however, be possible in a partial gravity environment such as a chamber in Earth orbit or on the surface of the Moon. This paper considers the feasibility of this and provides preliminary estimates of the main parameters involved.
Reliability, safety and civil aviation
Authors: Tait N. R. S.
Published: July 2016

Reliability and safety criteria have, in one form or another, made a significant contribution to engineering design since the earliest times. They gained added significance in Victorian times as the scale of civil and mechanical engineering projects increased. Codes of practice came into use, based both on practical experience and theoretical knowledge. Redundancy and diversity, though not given those names, were introduced as a means of achieving improved reliability and safety. Reliability and safety technology in the modern sense only developed, however, when predictive techniques, based on statistical information, were introduced. This technology has now taken its place in a wide range of engineering activities and is adopting an increasingly international role. It makes use of numerical reliability and safety goals and pays attention to problems associated with human reliability and ergonomics. This paper reviews the particularly important contribution made by civil aviation to the development of present day reliability and safety technology.
Demonstration of aircraft dynamic stability and response for aeronautical engineering students
Authors: Bloy A.W.
Published: July 2016

The teaching of aircraft stability and control at university usually progresses to the complexity of six degrees of freedom with a large array of aerodynamic, gravitational and inertial terms. It is therefore essential to ensure that students have a good grasp of fundamental dynamic characteristics such as damping and natural frequency, and any demonstration in which students observe aircraft motion is particularly helpful. At Manchester University this is achieved by a windtunnel demonstration of aircraft dynamic stability and response in pitch to a sinusoidal gust generator.
An experimental and computational investigation of ground effect lift loss for single jet impingement
Authors: Ing Dan N. , Zhang Xin
Published: July 2016

An investigation was carried out to study the parameters affecting single-jet ground-effect hover lift loss and to identify the cause(s) behind the large discrepancies in lift loss between the experiments of Wyatt of RAE Bedford and Corsiglia et alof Nasa Ames. The cause of the discrepancies was traced to a single geometrical parameter: baffle plate edge geometry, which significantly affected the flow separation underneath the plate. In contrast, the out-of-ground lift loss is insensitive to the edge geometry, but can be significantly affected by room size restriction. The investigations have highlighted the importance of accurately representing the edge geometry in ground effect testing of Vstol aircraft, and the importance of the test environment when conducting out-of-ground hover experiments.
Axisymmetric afterbody experiments for CFD validation
Authors: Miller P. , Agrell J. , Olsson J. , Sjörs K.
Published: July 2016

An experiment is described which was undertaken specifically to provide CFD validation data for the case of transonic flow over nozzle afterbodies. The tests were undertaken with the AGARD standard 10° and 15° axisymmetric boat-tail geometries. Onset Mach numbers in the range 0·80-0·99 and subsonic and under-expanded jet plumes were employed in the tests. Test conditions were selected which provided a range of afterbody flow features from largely attached to shock-induced separated flows. A uniquely detailed set of surface pressure and flowfield data are presented. The flow data were acquired with a two-component laser Doppler anemometer (LDA) and define the mean and fluctuating flow components at about 500 spatial locations for each of these complex transonic flowfields. Additional information was recorded which fully defines the required computational boundary conditions.

Also presented is a detailed study of the necessary attributes of windtunnel CFD validation data. It is demonstrated that relatively high blockage experiments using cost-effective windtunnels can be used to generate CFD validation data if proper account is taken of the model/tunnel interference.
Yaw control by tangential forebody blowing
Authors: Wood N.J. , Crowther W.J.
Published: July 2016

Aircraft yaw control at high angles of attack by tangential forebody blowing has been investigated experimentally. Tests were performed in the University of Bath 21 m x 1.5 m low speed wind tunnel using a 6% scale generic combat aircraft model fitted with blowing slots in the nose cone. Six component strain gauge balance force and moment data were measured for angles of attack up to 90° for various slot geometries and locations. The effect of slot azimuthal location is demonstrated and a slot stall phenomenon described. A geometry dependent forebody/wing flowfield coupling has been identified which can lead to unexpected yawing and rolling moments. The primary source of yawing moment is shown to be the enhanced area of attached flow on the blown side of the forebody rather than direct vortex influence.

The optimum slot extent and location depend on the angle of attack range over which control is required. For regions where steady vortex asymmetry is present, slots near the apex of the forebody produce severe control reversals at low blowing rates. These reversals can be minimised by placing the slots away from the apex. For control in regions where the flow is dominated by periodic vortex shedding, long slots offer efficient control to 90° angle of attack. The most suitable compromise for wide range control would appear to be a short slot placed away from the apex of the forebody.
A comparison of several eddy viscosity turbulence models in two and three dimensional boundary layer flows
Authors: Leung A. W. C. , Squire L. C.
Published: July 2016

Four flow cases are calculated using a boundary layer method with five turbulence models. The Johnson-King model, in particular, is modified and two variant forms are used in the present work. The variant forms involve an anisotropic form of three-dimensional eddy viscosity formulations and a modification in the outer viscosity expression. It is found that the Johnson-King model generally performs very well as compared to the others, and the variant forms provide further improvement in most cases.
Transition of compressible high enthalpy boundary layer flow over a flat plate
Authors: He Y. , Morgan R. G.
Published: July 2016

This paper presents the results of an experimental investigation into the characteristics of boundary layer transition to turbulence in hypervelocity air flows. A series of experiments was conducted using a flat plate model, equipped with static pressure and thin film heat transfer transducers, in a free piston shock tunnel. Transition was observed in the stagnation enthalpy range of 2·35 to 19·2 MJ/kg. The transition Reynolds number correlates well with the unit Reynolds number through a simple empirical relation. The influences of Mach number, pressure and wall cooling are examined. The measured heat transfer rates in laminar and turbulent regions are compared with empirical predictions. Freestream disturbances of the test flow were also measured and analysed.
A hybrid integral equation finite volume scheme for transonic potential flow about complex configurations
Authors: Bhattacharya A. K. , Arora N. L.
Published: July 2016

A hybrid integral equation finite volume scheme has been developed for the calculation of transonic potential flow about complex configurations. A new technique has been used for evaluating the potential values in the field cells intersecting the body surface panels. These potential values then serve as Dirichlet boundary conditions for computing the potentials in the field by a finite volume Successive Line Over Relaxation (SLOR) scheme. In this approach there is no need to evaluate the potentials anywhere in the field by direct application of Green's third identity, thus significantly reducing computer processing time and storage requirement, while improving accuracy of surface pressure prediction and shock capture, as results indicate. The capability of tackling additional complex geometry with ease, the primary advantage of the integral equation approach, is demonstrated by using the same field grid for wing-alone and wing-body combination cases, while maintaining the solution accuracy.
Passive control of pre-entry shock in supersonic intakes
Authors: Rolston S.C. , Raghunathan S.
Published: July 2016

Passive boundary layer control experiments were conducted on a small supersonic sidewall intake at a Mach number of 1·46 to study the possibility of controlling and improving the intake performance by such a control. The passive control configurations tested included a suction slot in the intake duct located down stream of the shock system (1) connected by a breather passage to a narrow tangential injection slot upstream of the intake and (2) vented to a location where the pressure is free stream static pressure and well away from the inlet of the intake. The results of the experiments showed, that for a supersonic intake, passive control can control the pre-entry shock position, reduce the shock interaction losses and improve the overall pressure recovery.
Aeroelasticity analysis of a bird-damaged fan assembly using a large numerical model
Authors: Imregun M. , Vahdati M.
Published: July 2016

Bird strike is a major consideration when designing fans for civil aero engines. Current methods rely on impact tests and structural optimisation but it is highly desirable to have predictive numerical models to assess the aerodynamic and aeroelastic stability of bird-damaged fan assemblies. A detailed feasibility study towards such a prediction capability, consisting of a CFD solver coupled to a finite element representation of the structure, is reported in this paper. A whole-assembly model was used for both the fluid and the structural domains, an approach necessitated by the loss of cyclic symmetry due to one or more blades undergoing plastic deformation under the effect of the bird impact. It was assumed that two consecutive blades had suffered unequal amount of bird damage, the so-called heavy and medium-damaged blades.
Simulation of parallel blade–vortex interaction using a discrete vortex method
Authors: Qian L. , Vezza M.
Published: July 2016

Numerical results are presented for two-dimensional vortex-aerofoil interaction using a grid-free discrete vortex method. The effects of the passing vortex on the surface pressure distribution and hence the aerodynamic force and moment of the aerofoil are examined in detail for a variety of interaction geometries. For some head-on interaction cases, vortex-induced local flow separation is also predicted on the aft part of the aerofoil surfaces. Extensive comparisons are made with other numerical results and the results from the Glasgow University BVI wind-tunnel test, which show good agreement.
Optimisation of air-jet vortex generators with respect to system design parameters
Authors: Bray T. P. , Garry K. P.
Published: July 2016

A simple technique is proposed that allows the definition of the geometry and characteristics of an air-jet vortex generator to be defined, using the system requirements in practical design. Typically, the aircraft designer is concerned with the mass flow-rate and air pressure requirements of any pneumatic system for inclusion to an airframe. These parameters are not congruent with those for air-jet vortex generator aerodynamic design, and therefore, some tool is required to bridge the gap.

Such a tool is proposed, based on empirical methods for the prediction of air-jet vortex generator behaviour. The technique allows the comparison of the vortex strength, and the system inputs (the jet mass flow-rate and the air-jet plenum pressure) for the air-jet, for a range of jet nozzle diameters and jet velocity ratios. Through this comparison, the optimum air-jet design can be reached for a given system input.
A case for multi-level optimisation in aeronautical design
Authors: Robinson G. M. , Keane A. J.
Published: July 2016

This paper discusses how the inevitable limitations of computing power available to designers has restricted adoption of optimisation as an essential design tool. It is argued that this situation will continue until optimisation algorithms are developed which utilise the range of available analysis methods in a manner more like human designers. The concept of multi-level algorithms is introduced and a case made for their adoption as the way forward. The issues to be addressed in the development of multi-level algorithms are highlighted.

The paper goes on to discuss a system developed at Southampton University to act as a test bed for multi-level algorithms deployed on a realistic design task. The Southampton University multi-level wing design environment integrates drag estimation algorithms ranging from an empirical code to an Euler CFD code, covering a 150,000 fold difference in computational cost. A simple multi-level optimisation of a civil transport aircraft wing is presented.
Computations of bladerow stall inception in transonic flows
Authors: He L. , Ismael J. O.
Published: July 2016

A three-dimensional unsteady Navier-Stokes solver has been used to simulate stall inception in a single row ten passage segment of a transonic fan, the NASA rotor-67. At subsonic flow conditions, the 3D results illustrate a rotating stall inception with short scale part-span cells rotating at around 80% rotor speed, similar to that observed in some low speed experiments. However, at a supersonic relative inflow condition, the results show that an isolated blade row tends to stall in a one-dimensional breakdown pattern without first experiencing rotating stall. At near-stall conditions, significant self-excited unsteadiness is generated by the interaction between the tip-leakage vortex and the passage shock wave. Further computations for two-dimensional configurations indicate that it is possible to have a rotating pattern of instability in transonic blade rows associated with circumferential synchronised shock oscillation.
Effect of heat transfer on periodic transonic flows
Authors: Mitchell D. A. , Cooper R. K. , Raghunathan S.
Published: July 2016

The effects of the model surface to free stream adiabatic temperature ratio(Tw/Tad)on periodic transonic flow over a 14% thick biconvex aerofoil are evaluated using a computational fluid dynamic approach. The analysis is based on the thin layer Navier Stokes equations with Baldwin-Lomax turbulence model. The results of computations showed that on biconves aerofoils there is a large effect of heat transfer on instantaneous pressure distributions and periodic buffet excitation level confirming some of the available experimental data. The effects observed have an implication in wind tunnel measurement of buffet associated periodic transonic flows.
Alleviation of pitch-up on delta wings using distributed porosity
Authors: Traub L. W. , Moeller B. , Galls S. F.
Published: July 2016

An experimental investigation was undertaken to determine the effectiveness of distributed surface porosity for the alleviation of pitch-up on a delta wing. Tests were undertaken using a 65° sweep delta wing with distributed porosity evaluated at various locations on the wing. Force balance, on and off surface flow visualisation and flow field surveys using a multi-hole probe were undertaken. The data shows that distributed porosity applied along the wing leading edge at the apex is effective in eliminating pitch-up whilst incurring a minimal performance cost. Trailing edge porosity generally degraded performance.
Control and handling qualities considerations for an advanced supersonic transport aircraft
Authors: Steer A. J. , Cook M. V.
Published: July 2016

A future advanced supersonic transport aircraft (AST) has fundamental characteristics and problems inherent to supersonic cruise aircraft with corresponding unique control and handling characteristics.

In order to optimise the aerodynamic performance across the full flight envelope a fully integrated flight and propulsion control system will be required. However, this will need to be designed from the outset within clearly defined flight control and performance guidelines.

Relevant existing and AST specific handling qualities criteria will need to be developed if a successful commercial transport aircraft is to be produced.

This paper begins by presenting an overview of existing supersonic transport (SST) aircraft operations and current second generation SST research activities and design considerations. This is followed by an analysis of the principal aerodynamic, dynamic and control characteristics of SST and AST aircraft and their effect on the aircraft’s handling qualities. Finally, some possible solutions to the control and handling issues are investigated, assessed and presented.
The design challenge of high altitude long endurance (Hale) unmanned aircraft
Authors: Jones R. I.
Published: July 2016

The requirement for an aircraft to operate in the thin atmosphere at high altitudes for long periods provides a particular challenge to all areas of aeronautical engineering. This is reflected in a range of difficulties encountered when attempting to design aircraft for this type of operation.

This paper first considers the reasons for adopting an unmanned solution for high altitude long endurance (Hale) aircraft. It then indicates how the demands of Hale operations lead to problems in applying the design approach taken for more common aircraft types. Some of the work performed at the College of Aeronautics (CoA), in attempting to address the problem areas for the design process and produce initial designs for a range of Hale unmanned aircraft (UMA) types, is then reviewed. The lack of data/methods to allow the prediction of Hale UMA structure mass, engine performance at high altitudes and aerodynamic parameters for low Reynolds number operation and high aspect ratio configurations are identified as particular problems. However, initial design, based on standard approaches, has been shown to be possible, provided caution is exercised.
Development and assessment of computer methods for three-dimensional turbulent boundary layers
Authors: Wu J. , Müller U. R.
Published: July 2016

This paper describes the development of a finite difference method that solves the boundary-layer equations for three-dimensional compressible turbulent flows. The most prominent achievements are the employment of a Newton technique for the simultaneous solution of all governing equations, an option to choose an algebraic or ak-εeddy-viscosity turbulence model, and the flexible use of curvilinear coordinates. The method is validated by comparisons with a number of experimental and theoretical data sets of three-dimensional, compressible and incompressible, steady and unsteady boundary layers. In parallel, the performance of a three-dimensional compressible industrial integral boundary-layer technique is evaluated by comparisons with experimental test cases and with the results of the field method.
Parallel implementation of an upwind Euler solver for hovering rotor flows
Authors: Allen C. B. , Jones D. P.
Published: July 2016

An Euler method for computing compressible hovering rotor flows is described. The equations are solved using an upwind finite-volume method in a blade-fixed rotating co-ordinate system, so that hover is a steady problem. Transfinite interpolation, along with a periodic transformation, is used to generate grids for the periodic domain. Computation of these flows to an acceptable accuracy requires fine grids, and a long integration time for the wake to develop, resulting in excessive run times on a single processor. Hence, the method is developed as a multiblock code in a parallel environment, and various aspects of data passing and communication between processors have been considered. It is shown that a considerable increase in performance is available from the use of non-blocking and asynchronous communication. It is also demonstrated that increased performance may be available by balancing the residual levels rather than the number of cells on each processor.
Finite-state aerodynamic modelling for gust load alleviation of wing–tail configurations
Authors: Gennaretti M. , Ponzi C.
Published: July 2016

A finite-state aerodynamics methodology is proposed for the analysis of the forces generated by a gust. To illustrate and assess the methodology, gust-response and gust-alleviation applications are included. Finite-state aerodynamics denotes a technique to approximate aerodynamic loads so as to yield an aircraft model of the type ẋ = Ax + Bu (state-space formulation). In this paper, a finite-state formulation is proposed to include the presence of a gust. The aerodynamic loads to be approximated are evaluated here by using a frequency-domain boundary-element formulation; the flow is assumed to be irrotational except for a zero-thickness vortex layer (wake). The gust-alleviation application consists of determining a control law for reducing the response to a vertical gust disturbance, as measured by the centre of mass acceleration. Two optimal-control approaches are considered for the synthesis of the control law: one uses the classical linear-quadratic regulator (LQR), whereas the second includes the additional feed-forward of the gust velocity ahead of the aircraft. Deflections of ailerons and elevators are assumed to be the control variables. Numerical results deal with responses to both a deterministic ‘1 – cosine’ gust distribution and a stochastic von Kármán spectrum. They indicate that the finite-state aerodynamic model proposed is capable of approximating, with a high level of accuracy, both the aerodynamic loads induced by the aircraft kinematics variables and those induced by the control variables, over a wide frequency range.
Shock phenomena in high speed aerodynamics: still a source of major concern
Authors: Délery J. M.
Published: July 2016

Shockwaves are present in a flow as soon as the Mach number becomes supersonic. Being viscous phenomena, Shockwaves are a source of drag which can be predominant when the Mach number is significantly higher than one. In supersonic air intakes, the production of entropy by shocks is felt as a loss in efficiency. At high Mach numbers, Shockwaves produce a considerable temperature rise leading to severe heating problems, complicated by real gas effects. The intersection - or interference - of two shocks gives rise to complex wave patterns containing slip-lines and associated shear layers whose impingement on a nearby surface can cause detrimental pressure and heat transfer loads. The impact of a Shockwave on a boundary layer is the origin of strong viscous interactions which remain a limiting factor in the design of transonic wings, supersonic air intakes, propulsive nozzles and compressor cascades. More effort is needed to improve prediction of these interactions and to devise new techniques to control such phenomena.
The effect of wing planform shape on dynamic stall
Authors: Coton F. N. , McD. Galbraith R. A. , Green R. B.
Published: July 2016

This paper examines the dynamic stalling of three wing planforms and characterises the main features of the stalling process in each case. The particular data were obtained during a three year research programme in the Department of Aerospace Engineering, University of Glasgow to collect high-resolution unsteady pressure data on the dynamic stalling characteristics of finite wing planforms. In this study, which was motivated by the pressing need for a greater understanding of the strongly three-dimensional effects in the tip region of helicopter rotors, the three wing planforms considered were a straight rectangular wing, a rectangular wing with swept tips and a delta wing. The initial test programme was followed by a further three years of detailed analysis and interpretation of the test data. Results from this analysis are presented in the present paper for cases in which the wings were subject to ramp motions.
Helicopter encounters with aircraft vortex wakes
Authors: Padfield G. D. , Turner G. P.
Published: July 2016

This paper presents the results of a study into wake vortex-related safety issues associated with simultaneous rotary and fixed-wing aircraft operations at busy airports. An analysis conducted using both simple analytic models and high fidelity FLIGHTLAB simulations has considered a helicopter located in the hover above the landing point and during approach and landing. Tip vortices from a Boeing 747 are shed and are assumed to be travelling in a horizontal plane by the time they reach the helicopter. A worst case scenario is simulated, with no vortex ageing or attenuation due to ground effect.Bothsimple and high fidelity simulations indicate that the rates of climb and descent induced by the vortex tails can be significant. When the helicopter flies through the vortex core, moderately large transient excursions in attitude occur within a few seconds. When the helicopter does not pass through or close to the core, while the flight path perturbations are still significant, the attitude response is shown to be significantly reduced. The predicted cyclic control power required to counteract the vortex-induced hub moments is about 40% of full control, compared with more than 100% for an ‘equivalent’ fixed-wing aircraft. The control power required in the vertical, collective, axis to overcome the downdraught and updraught in the vortex tails can be as high as 15–20%. While the authors have not tried to make judgements as to whether pilots would find the transients manageable, an approach to quantifying the extent of the hazard has been suggested using the failure transients criteria from the handling qualities performance standard ADS–33. Combined with analysis of the likelihood of such occurrences at particular airports, such response criteria offer a rational approach to developing safety cases for simultaneous operations.