bluuebunny/crossref_metadata_2025_split huggingface dataset:
A statistical analysis of the surface pressure distribution on a delta wing
Authors: Jupp M. L. , Coton F. N. , Green R. B. 
Published: July 2016

AbstractThis paper describes and presents results from static wind tunnel tests conducted on a 60° delta wing at a root chord Reynolds number of 2·7 x 106. In these tests, the wing was instrumented with 192 miniature pressure transducers which, in conjunction with a powerful multi-channel data-logging system, allowed the distribution of time-varying surface pressures to be measured at high temporal resolution. Analysis indicates that the distribution of root mean square pressure on the leeward surface of the wing can provide considerable insight into the behaviour of both the primary and secondary vortex structures. In addition, it has been established that the frequency content of pressure signals measured in the vicinity of these vortex structures is sensitive to the vortex state. It is suggested that these data features can be directly attributed to previously observed behavioral characteristics of the vortex breakdown process.
A new induced-drag prediction method using Oswatitsch’s expression
Authors: Veilleux C. , Masson C. , Paraschivoiu I. 
Published: July 2016

AbstractThis paper presents a critical study related to the evaluation and breakdown of total wing drag based on solutions of the Euler equations for subsonic and transonic three-dimensional flows.This study clearly identifies the false entropy production present in all discretised Euler solutions as the main source of the discrepancies between the drag predictions produced by body-surface pressure integrations and far-field methods. A good understanding of the entropy production mechanisms present in discretised threedimensional Euler solutions has lead to an original procedure for the total drag breakdown and a new method for the evaluation of the induced drag. This new technique is based on body-surface pressure integrations and Oswatitsch’s expression integrated over suitable integration surfaces. In contrast with the various methods for the drag breakdown and the evaluation of the induced drag available in the literature, the proposed technique uses an exact formulation and is simple to implement. Using detailed drag calculations on an elliptic wing (theXt= 1·0 wing) and the ONERA M6 wing, it has been shown that this new technique is not strongly sensitive to grid refinement and to the level of false entropy production in the calculation domain.
Vulnerability prediction method for use in aircraft conceptual design
Authors: Al-Ahmed S. , Fielding J. P. 
Published: July 2016

AbstractA methodology has been developed to integrate the vulnerability discipline into the conceptual/preliminary design process of combat aircraft. An interactive and programmable solid modelling Computer Aided Design (CAD) system is used to generate a CAD solid model of the aircraft’s critical components. The aircraft’s components’ sizes and shapes are pre-defined by a conceptual/preliminary design synthesis computer model. A systematic Child-Parent assembly process is used to model the aircraft vulnerability, by defining the criticality degree of each component in the aircraft assembly. Solid Modelling CAD techniques have been modified to develop techniques to perform the two main standard vulnerability assessments, namely the shotline and vulnerable area methods.
Pressure over a dual-cavity cascade at supersonic speeds
Authors: Zhang X. , Edwards J. A. 
Published: July 2016

AbstractPressure distributions over a dual cavity cascade were studied at supersonic speeds of Mach 1·5 and 2·5. The study was performed through numerical modelling and results compared with model measurements. The Reynolds-averaged Navier-Stokes equations were solved using a finite-volume algorithm in which the inviscid cell interface fluxes were estimated using Roe's approximate Riemann solver with a second-order extension, and turbulence was modelled using a two-equationk-mmodel with compressibility corrections. Two test configurations were selected: (1) a length-to-depth ratioL/D =1 cavity followed by anotherL/D= 1 cavity, and (2) anL/D= 3 cavity followed by anL/D =1 cavity. The prediction was compared with that of a single cavity of the sameL/D.It was found that the pressure field around theL/D =1 cavity was substantially modified by a precedingL/D =3 cavity. Changes in the pressure and pressure drag coefficient were observed. The study clarified some earlier observations of unsteady modes over a dual cavity cascade, and confirmed model measurements of the pressure fluctuation under a number of flow and geometry conditions.
Wavelet analysis of pilot workload in helicopter low-level flying tasks
Authors: Jones J. G. , Padfield G. D. , Charlton M. T. 
Published: July 2016

AbstractAs part of a programme of research to improve mission effectiveness by studying pilot workload and task performance in mission-oriented flight tasks, a methodology has been developed in which wavelet analysis is used to extract information from records of vehicle response and of pilot control activity. By decomposing the records into discrete wavelets, components of vehicle agility and pilot workload are derived in the form of wavelet-based ‘quickness’ parameters for vehicle agility and so-called ‘attack’ parameters for pilot workload. It is shown how individual wavelet components in the records of pilot control activity, referred to as ‘worklets', can be associated with the sub-tasks of ‘guidance’ and ‘stabilisation'. It is demonstrated how these concepts can be applied to quantify changes in pilot control activity associated with increasing task difficulty or changes in aircraft handling qualities. Two examples are presented, one from a flight trial in which the task difficulty was increased by changes in a prescribed ground track and the other from a simulation trial in which an increased time delay was introduced into the response of the flight control system.
Experimental investigation into transonic flows over tandem cavities
Authors: Taborda N. , Bray D. , Knowles K. 
Published: July 2016

AbstractAn experimental study was conducted to analyse the pressure distribution along the floor of a cavity, with and without the presence of an upstream tandem cavity, at a constant freestream Mach number of about 0-911. Measurements were made for single cavities and the results compared with those obtained in the presence of an upstream tandem cavity. This comparison was made over a wide range of geometries, covering open to closed classes of cavities with both identical and different dimensions for the two cavities. The effect of the spacing between the two cavities was also studied. The downstream cavity is shown to be significantly affected by the presence of an upstream cavity, with both the overall net static pressure and its gradient being affected, dependent upon the class of cavity geometry and spacing under consideration.
Flow regimes associated with yawed rectangular cavities
Authors: Czech M. , Savory E. , Toy N. , Mavrides T. 
Published: July 2016

AbstractThe present work is concerned with the aerodynamics of the turbulent boundary-layer flow over yawed rectangular cavities with the focus on the steady and unsteady pressures generated by the interaction. Cavities with a planform aspect ratio of 4-85 and streamwise length to depth ratios from 1 to 3 were studied experimentally in a low-speed wind tunnel.The results indicated three main types of cavity flows. The shear layer bridges the cavity for small angles between mean flow direction and minor cavity axis. The flow field remains almost two-dimensional with little change in drag coefficient. Strong instabilities, associated with a rise in drag coefficient, are found when the cavity is yawed to greater angles. An aerodynamic feedback mechanism depending on interactions between the separated shear layer and the cavity fluid is suggested as the mechanism responsible for the generated oscillations. The influence of the cavity depth is, hereby, found to be fundamental as it determines the degree to which interactions between the separated shear layer and the cavity base occur. As a result both the magnitude and the frequency of the instabilities are a function of the cavity depth. When rotating to higher angles a greater portion of the shear layer reattaches to the cavity base which leads to a loss of flow organisation and a significant increase in drag.
Energy requirements for the flight of micro air vehicles
Authors: Woods M. I. , Henderson J. F. , Lock G. D. 
Published: July 2016

AbstractThis paper describes power requirements for micro air vehicles, flying in the Reynolds number regime of -lO*. Three flight modes have been researched: fixed wing, rotary wing and flapping wing. For each mode, the literature in the public domain has been reviewed to obtain appropriate lift and drag coefficient data at these low Reynolds numbers. Energy and power requirements for the three flight modes have been calculated and an optimisation procedure has been utilised to evaluate the most efficient flight mode and configuration for a variety of specified missions. The effect of wind-speed on the optimal solution has been examined. It has been discovered that when there is no hover requirement, fixed wing flight is always most energy efficient for the micro air vehicle. However, if there is a hover requirement, the suitability of flapping or rotary wing flight is dependent on the mission profile and ambient windspeed.
Development and application of farfield drag extraction techniques for complex viscous flows
Authors: Hunt D. L 
Published: July 2016

AbstractA new method for deriving the components of drag from the CFD solution of an aircraft flowfield, by analysis of its wake, is presented. This method is applied to viscous flow calculations. It is also applied to configurations containing powerplants. The drag values predicted by this method are compared with the values obtained using more traditional methods, and good agreement is demonstrated.
Assessment of turbulence model performance for transonic flow over an axisymmetric bump
Authors: Hasan R. G. M. , McGuirk J. J. 
Published: July 2016

AbstractA computational study has been performed to evaluate the predictive capabilities of some existing eddy-viscosity (both linear, LEVM, and non-linear, NLEVM) and Reynolds stress transport turbulence models (RSTM) by reference to a transonic shock-induced separated flow over a 10% axisymmetric bump. The calculations have been carried out during the course of a collaborative research programme including both UK universities and industry. The findings of the project demonstrate that improved results can be obtained for such flows by using more advanced turbulence models. For linear eddy-viscosity models, only the SST approach gave good predictions of shock location, recirculation size and pressure recovery, although this was accompanied by deficiencies in the prediction of post-shock velocity profile shape. Non-linear eddy-viscosity models, particularly at the cubic level, provided a more consistent level of agreement with experiments over the range of shock location, wall pressure and velocity profile parameters. Some improvement was also seen in the prediction of turbulence quantities, although only a move to an RSTM closure model reproduced the measured peak stress levels accurately. It was notable that the use of low-Re variants of the models (instead of wall functions) produced no significant improvement in predictions. There are, however, some shortcomings in all models, particularly in the development of flow after reattachment, which was always predicted to be too slow.
Lord Kings Norton — his contribution to the gas turbine aero engine
Authors: Evans Mike 
Published: July 2016

The twentieth century has seen man’s mastery of the air, and fundamental to that achievement has been the provision of power to sustain the process of flight. For the first forty years the piston engine reigned supreme, yet for even longer now the power to fly has been provided by the gas turbine. In the conception and development of this prime mover Britain can justly claim to have led the world.Two servants of the Crown quite independently had the vision and that amalgam of creative and analytical powers to see what might lie beyond the piston engine — one a scientific civil servant working at the Royal Aircraft Establishment (RAE) and the other, remarkably, a young RAF officer already distinguishing himself as a pilot. But the birth of the jet engine proved to be a painful process. While early aircraft designers had embraced the piston engine, neither Government nor the aircraft or aero engine industry showed interest initially in the gas turbine. The change in attitude began when war approached in 1939 and thereafter accelerated in the effort to move from bench demonstrator status to a full-production engine capable of contributing to the outcome of the war. It was in this difficult and complex process of transition that Dr Harold Roxbee Cox — Lord Kings Norton — was to play such a vital role. To appreciate his achievements it is appropriate to remind ourselves of the progress — or lack of it — on the gas turbine prior to his becoming involved.
3.5. High-resolution ISOCAM view of nuclear and circumnuclear starbursts in barred galaxies
Authors: Friedli D. , Wozniak H. , Martinet L. , Pfenniger D. 
Published: July 2016

Non-axisymmetric gravitational potentials are likely to play an important role in generating central activity in galaxies, i.e. starbursts and/or active galactic nuclei (AGN). For instance, the often observed secondary bars embedded in larger, primary, ones (Friedli & Martinet 1993; Wozniak et al. 1995; Friedli et al. 1996) might play a key role in feeding AGN, by accreting gas down to the centre at scales of a few parsecs. On the other hand, the frequent presence of a nuclear ring of star formation located between both bars indicates that double-barred galaxies are intimately linked to the formation of some circumnuclear starbursts. This type of galaxies might give useful clues to the connection between starbursts and AGN.Below, as part of a larger sample of nearby barred galaxies (Wozniak et al. 1997a) being taken by ISOCAM on board of the ISO satellite, we briefly discuss the characteristics of the circumnuclear mid-infrared (MIR) emission of two double-barred galaxies, namely NGC 4321 (M100) and NGC 1097. The observations were done using LW2 (5–8.5μm) and LW3 (12–18μm) broad band filters at the 1.5″ px−1 PFOV.
4.10. Statistical properties of dense molecular clouds in the Galactic center region
Authors: Miyazaki Atsushi , Tsuboi Masato 
Published: July 2016

Data : We used the Galactic center region survey data in CS J=1-0 with the Nobeyama 45-m telescope (Tsuboi, Handa, and Ukita 1997).Cloud Definition : We identified molecular clumps in the positive longitude region of about ∼1deg2 (+0°10′ < l< + 1°42′ and −25′ < b< +25′) within all survey region.
5.14. NMA survey of HCN and CO emission from nearby active galaxies
Authors: Kotaro Kohno , Ryohei Kawabe , Kazushi Sakamoto , Sumio Ishizuki , Vila-Vilaro Baltasar 
Published: July 2016

In order to study the spatial variation of molecular gas properties and their relation to the nuclear activities of galaxies, we have conducted an imaging survey of HCN(1-0) and CO(1-0) emission from nearby active galaxies with the Nobeyama Millimeter Array. Here we present the results of three galaxies, NGC 3504 (Starburst nucleus), NGC 4736 (Post-Starburst nucleus), and NGC 6951 (Seyfert nucleus with a circumnuclear star-forming ring).In the observations of these three galaxies, we find that (1) the HCN distribution is significantly different from that of CO, and that (2) the HCN emission spatially correlates better with the massive star-forming region than CO emission (Figure 1, 2(a), and 2(b)). For instance, in the Post-Starburst nucleus of NGC 4736, we find a remarkable decrease of the HCN emission, despite of strong CO nuclear concentration. The upper limit (2σ) of the integrated intensity ratio I(HCN)/I(CO) within the central r < 150 pc region is 0.04, which is surprisingly low compared with the value in other galactic nucleus (cf. ratio = 0.08 within r < 300 pc in Milky Way, Jackson et al. 1996, ApJ, 456, 91). Presumably the dense molecular gas must have been consumed by a past starburst event in the nucleus. These results suggest a tight correlation between the gas density measured by the I(HCN)/I(CO) ratio and the star-forming activities in the central region of galaxies.It seems that there exist a spatial anti-correlation between the I(HCN)/ I(CO) ratio and the gas velocity dispersion in NGC 6951 (Figure 2(c)). The ratio is not enhanced in the CO twin peaks which are interpreted as shock regions due to gas orbit crowding. These imply the importance of gravitational instability on the formation of dense molecular gas and successive massive starformation in this region.
6.8. A multi wavelength study of the circumnuclear region of NGC 1365
Authors: Kristen H. , Sandqvist Aa. , Lindblad P.O. 
Published: July 2016

The nuclear region of the supergiant barred spiral galaxy NGC 1365 contains bright “hot spots”, as seen at optical wavelengths, as well as a number of non-thermal radio continuum sources, some of which remain unresolved at 0.25” × 0.10” resolution (Sandqvist et al. 1995, A&A 295, 585).The distribution of [OIII] λ5007 emission from the nuclear region supports the scenario of an [OIII] cone emanating from the Seyfert nucleus. The velocity field of the high excitation gas in the cone has been modeled by Hjelm & Lindblad (1996, A&A 305, 727) in terms of an accelerated bipolar conical outflow. Such conical or biconical high-excitation emission-line structures extending from the position of the nucleus are found in several active galactic nuclei.
8.7. Magnetospheric structure filled by relativistic plasma jets/winds
Authors: Nitta Shin-Ya 
Published: July 2016

Recent observations revealed that many kinds of astrophysical outflows have very similar structure, i.e. bipolar jets are surrounded by an equatorial (disk-shaped) wind or an expanded wind as in the outflows from YSO's, post AGB stars, pulsars or AGN's. One might think that this is very queer because the species of the central objects and the spatial scales are quite different among these objects. However this similarity is a result of self-organized magnetospheric equilibrium. In these systems, the rotating magnetic field plays an important role for the structure formation. In such systems, two components of the Lorentz force (the electrostatic force and the magnetic force arising from the toroidal component) dominate other forces in the region far distant from the rotation axis in spite of the difference of the acceleration mechanism of the flows. We can understand that such similarity of the structures is a nature of the plasma outflows itself.We suppose relativistic, pressure-free, inviscid, resistive-less, stationary and axisymmetric MHD flows. In this case, MHD equations reduce to well known basic equations: the Bernoulli equation and the Grad-Shafranov equation. We should note that the special relativistic treatment is necessary to discuss the structure far beyond the light cylinder, even if the flow speed is not close to the light velocity.
Recent Progress in Solar or Stellar Interior Modelling
Authors: Turck-Chièze S. 
Published: July 2016

Acoustic modes are well-suited probes to check the internal stellar structure and bring interesting constraints on turbulence regions, mixing in stellar interiors and magnetic fields. The SOHO satellite, through the helioseismic instruments GOLF, MDI and VIRGO, has significantly improved the knowledge of these modes owing to an excellent duty cycle (greater than 90%) and the capability to detect very low amplitude modes, down to 3 mm/s. Five years of the SOHO misson guarantee an accurate view of the solar interior, weakly dependent on the turbulent surface, from the energy-generating core to the surface.The recent results allow us to verify some of the theoretical assumptions of stellar modelling. The tachocline layers, located in a narrow region at the base of the convection zone, support an hydro (or magnetohydro) dynamical instability which induces mixing and results in 7Li depletion in accordance with photospheric observations. On the contrary, central mixing is not favoured by the present observations. Nuclear reaction rates of the pp chain are now constrained by the behaviour of the sound speed and density. Döppler velocity measurements appear as an excellent technique to follow in real time the temporal evolution of the luminosity produced in the core. Some puzzling questions about dynamical effects in stellar plasmas can now start to be addressed for the first time. The theoretical neutrino emissions can be now directly deduced from our helioseismic vision of the energy-generating core.Nowadays, helioseismology provides a dynamical vision of the external half of the Sun (20% in mass), as a result of the extraction of the sound speed, density, rotation profiles and of the time evolution of velocity measurements. Below, the classical static vision of the nuclear region persists because of the poor spatial resolution offered by acoustic modes (±6% in radius, 10% in mass) and the long integration time (several years). Gravity modes will be extremely useful to improve the spatial resolution in the radiative region. The extended observations with the SOHO satellite may be extremely useful to detect some of these modes.
Vorticity, Current Helicity and Alpha-effect for Magnetic-driven Turbulence in the Solar Convection Zone
Authors: Rüdiger G. 
Published: July 2016

The turbulent electromotive force as well as the kinetic and current helicities have been computed for a turbulence subject to magnetic buoyancy and global rotation. The dynamo-alpha is found as positive in the northern hemisphere and negative in the southern hemisphere and the kinetic helicity has just the same signs.In agreement with the observations the current helicity is negative in the northern hemisphere and positive in the southern hemisphere. Our current helicities and alpha-effects are thus always out of phase. The signs of alpha-effect and both helicities exactly correspond to a numerical simulation by Brandenburg & Schmitt (1998).
The Search for Cold Molecular Gas in the Outer Galaxy
Authors: de Geus E.J. , Phillips J.A. 
Published: July 2016

It is well known that the rotation curves of many galaxies remain flat well outside their optical disks. This leads to the conclusion that the visible mass in galaxies is only a small fraction of the total (see e.g. Faber & Gallagher 1979). Although we are certain that “dark matter” exists, its composition and distribution are still unknown.In a recent paper Pfenniger et al. (1994) argued strongly for the possibility that dark matter could well be in the form of cold, predominantly molecular gas in a flat distribution. To have escaped previous detection in the outer parts of our Galaxy, the gas would need to have a low temperature and thus a low emissivity. Because most substantial heating sources of gas are associated with the presence of massive stars (UV radiation and cosmic rays) this requirement may be satisfied in the Galactic plane outside the optical disk.
Search for HI Bubbles Around WR Stars: WR 149
Authors: de Nicolau C. Cappa , Niemela V.S. , Herbstmeier U. , Koribalski B. 
Published: July 2016

The interaction of strong stellar winds with the interstellar medium creates large cavities or interstellar bubbles surrounded by expanding outer shells. 21-cm line (HI) observations have revealed the presence of such neutral gas bubbles around several WR stars (e.g. Niemela & Cappa de Nicolau 1991 and references therein; Dubner et al. 1992).Continuing our search for HI bubbles around WR stars, we have analyzed the neutral hydrogen distribution in the vicinity of the Wolf-Rayet star WR149, a highly reddened WN6-7 star located at 6.5 kpc in the direction (l,b) = (89.°53,+0.°65).