bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

AbstractThis 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

AbstractA 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

AbstractIon 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

AbstractIn 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

AbstractThis 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

AbstractThis 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

SummaryThe 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

AbstractThe 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

AbstractAn 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

AbstractA 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.
Airspace design: towards a rigorous specification of conflict complexity based on computational geometry
Authors: Fulton N.L. 
Published: July 2016

AbstractThe 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

AbstractA 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

AbstractThe 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

AbstractThe 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

AbstractThis 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

AbstractThis 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

AbstractA 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

AbstractRecent 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.
An experimental and computational investigation of ground effect lift loss for single jet impingement
Authors: Ing Dan N. , Zhang Xin 
Published: July 2016

AbstractAn 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

SummaryAn 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

SummaryAircraft 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

SummaryFour 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

AbstractThis 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

AbstractA 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

AbstractPassive 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.