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Si le sujet central en est bien le calcul théorique de la forme d'une aile d'avion au moyen des nombres complexes, domaine dans lequel s'est illustré Abraham de Moivre, cet article présente quatre moyens très différents qui permettent de parvenir à établir ces résultats. Après un bref rappel de la théorie du vol, une première partie est consacrée aux travaux expérimentaux de Gustave Eiffel, puis, en poursuivant l'ordre chronologique, on traite la méthode des singularités due à Nicolaï Joukovski, puis un procédé analogique développé par Joseph Pérès et Lucien Malavard, et enfin la technique contemporaine de résolution numérique des équations de Navier–Stokes. Si le recours à l'expérience en soufflerie subsiste de nos jours, les méthodes théoriques et analogiques, qui ont eu leurs heures de gloire au milieu du xx e siècle, sont aujourd'hui abandonnées, la puissance de calcul des ordinateurs les rendant désormais désuètes. Pour autant, elles constituent des manières très élégantes de résoudre le problème. [ABSTRACT FROM AUTHOR]

Abstract The historical evolution of the averaging concept in turbulence is presented according to a two-fold analysis, taking into consideration the physical meaning and the mathematical formulation. After having placed in their historical context some symptomatic characteristics of turbulent flows, the question of their interpretation as a turbulence syndrome, leading to a unitary identification of the phenomenon, is discussed. We then deal with the emergence of the notion of mean as a tool of physical understanding of such a unitary approach, and its relation with the progression of the "experimental" evidence. We conclude by relating this notion to the theoretical aspects of a determinism on average of the turbulent regime, its finality and some attempts to develop a probabilistic theory of turbulence. [ABSTRACT FROM AUTHOR]

Up until the twentieth century, fluid mechanics was characterised by a strong division between theory and practice. The formulas of mathematicians and physicists were difficult to apply experimentally and their relevance was neither well accepted nor well understood by engineers. In France, where priority was given to the theoretical aspects of this subject, the creation of several centres of fluid mechanics in the 1930s (Lille, Marseille, Paris and Toulouse) represented an attempt at a rapprochement between fluid mechanics, experimental aerodynamics, and hydrodynamics. The aim was to re-establish France's international profile, which had been lost after 1918. In Lille, the leadership of the “Institut de mécanique des fluides” (IMFL) was entrusted to Jospeh Kampé de Fériet, who was able to address questions of both theoretical and experimental nature in the context of his work at the IMFL and at the “Commission de la turbulence atmosphérique”. On the one hand, Kampé de Fériet used a probabilistic approach to give greater mathematical rigour to the statistical theory of turbulence due to Taylor–von Kármán. On the other hand, he played an active part in his group's experimental research on atmospheric turbulence. This paper aims to show in what way Kampé de Fériet's approach to fluid mechanics enabled him to contribute to the international development of the statistical theory of turbulence during the interwar period. [ABSTRACT FROM AUTHOR]

Les pales d’une éolienne sont soumises à des chargements aérodynamiques, génèrent des écoulements extrêmement complexes. Nous nous intéressons à la dynamique des écoulements autour des pales d’éolienne à axe horizontal en rotation. Ce papier présente une méthode de simulation numérique pour la prédiction de l’écoulement autour d’une éolienne à axe horizontal opérant en régime instationnaire, tridimensionnel turbulent utilisant l’approche basée sur les équations de Navier-Stokes moyennées (URANS) en utilisant le code ‘CFX’.Un maillage structuré a été adopté en utilisant la technique des interfaces (interface frozen rotor) entre le corps mobile (la pale) et le corps fixe (l’entourage). Le modèle de turbulence SST a été utilisé pour décrire l’écoulement turbulent. Les résultats de simulation ont été comparés avec les résultats expérimentaux, pour les conditions de rotation. En général, des bonnes concordances ont été notées. Une attention spéciale est portée sur les effets instationnaires, conséquents de rotation du rotor qui est mise en évidence par le calcul des pressions fluctuantes sur l’interface entre les parties fixes et mobiles en aval et en amont de la machine. Une analyse fréquentielle de ces signaux en utilisant une transformée de Fourier discrète (FFT) afin d’analyser le comportement instationnaire de la pale.

Dans cet article, nous présentons les résultats d’une étude des effets de la rugosité sur les performances aérodynamiques d’un profil de pale d’éolienne. Cette étude est effectuée par simulation numérique de l’écoulement turbulent autour du profil avec la résolution des équations moyennées de Navier-Stokes. La turbulence est représentée par le modèle de Menter. Les calculs sont exécutés en stationnaire à l’aide de Code_Saturne, un code libre d’EDF basé sous Linux. Dans une première étape, le Code_Saturne est appliqué à un profil S809 de surface lisse placé sous différentes incidences, de 0° à 25°. Ensuite, les simulations sont poursuivies pour un profil rugueux pour étudier les effets de la rugosité sur les caractéristiques aérodynamiques du profil. Les résultats obtenus sont en bonne corrélation avec les données expérimentales publiées.

Centrifugal compressors are used in many heat pumps and refrigeration systems. Radial vaneless diffuser is a principal component in these compressors. Therefore, the present research aims at improving the centrifugal compressor performance by optimizing the design of the radial vaneless diffuser. Two radial vaneless diffuser geometries were proposed, investigated and numerically optimized. The optimization aimed at minimizing the diffuser loss coefficient and maximizing the pressure coefficient. Simulations were performed by solving the Reynolds averaged Navier–Stokes equation under 2D axisymmetric condition. A genetic optimization algorithm was implemented in order to conclude the optimum diffuser geometry. 2D axisymmetric simulations with air and R134a as working fluids showed that the optimized geometry reduced the diffuser loss coefficient by up to 10% and increased the pressure coefficient by up to 3.8%. Additional 3D simulations with an impeller located before the diffuser were performed. These 3D simulations showed that the optimized diffuser geometry reduced the diffuser loss coefficient by up to 4.7% and increased the pressure coefficient by up to 6.6% under jet-wake and swirl flow conditions. [ABSTRACT FROM AUTHOR]

Bats are diverse, speciose, and inhabit most of earth's habitats, aided by powered flapping flight. The many traits that enable flight in these mammals have long attracted popular and research interest, but recent technological and conceptual advances have provided investigators with new kinds of information concerning diverse aspects of flight biology. As a consequence of these new data, our understanding of how bats fly has begun to undergo fundamental changes. Physical and neural science approaches are now beginning to inform understanding of structural architecture of wings. High-speed videography is dramatically expanding documentation of how bats fly. Experimental fluid dynamics and innovative physiological techniques profoundly influence how we interpret the ways bats produce aerodynamic forces as they execute distinctive flight behaviors and the mechanisms that underlie flight energetics. Here, we review how recent bat flight research has provided significant new insights into several important aspects of bat flight structure and function. We suggest that information coming from novel approaches offer opportunities to interconnect studies of wing structure, aerodynamics, and physiology more effectively, and to connect flight biology to newly emerging studies of bat evolution and ecology. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Journal of Zoology is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Les cyclones représentent des dispositifs très utilisés pour la séparation gazaérosols dans l’industrie. L’étude approfondie de l’écoulement turbulent tridimensionnel dans un cyclone est très complexe et demande des codes de calculs puissants. Nous proposons ici la simulation numérique d’un écoulement turbulent aérodynamique à travers un cyclone au moyen d’un code Fluent. Cette étude traite l’effet de la température et la vitesse d’entrée sur l’écoulement turbulent d’air dans un cyclone. Ceci est obtenu en appliquant deux modèles de turbulence qui sont, le modèle RNG k - et le modèle RSM (Reynolds Stress Model). Une comparaison des champs thermique et de vitesse moyenne des différents modèles de turbulence a été effectuée. L’attitude tridimensionnelle de l’écoulement a été confirmée. Il est à souligner aussi que la chute de pression augmente avec l’augmentation de la vitesse d’entrée et diminue avec l’augmentation de la température. Il est à signaler que le modèle des contraintes de Reynolds capte mieux les phénomènes dans un écoulement tourbillonnaire intense en présence des parois.

Ce papier présente une méthode de simulation numérique pour la prédiction d’écoulement autour d’une éolienne à axe horizontal opérant en régime stationnaire, en utilisant le code ‘Fluent’. L’objectif principal est de déterminer les caractéristiques aérodynamiques de la pale en état d’arrêt et en rotation. Les simulations ont été effectuées en considérant les équations de Navier-Stokes moyennées par la procédure de Reynolds. Un maillage non-structuré a été adopté et en utilisant la technique ‘moving reference frame’. Le modèle de turbulence Spalart-Allmaras a été utilisé pour décrire l’écoulement turbulent. Les résultats de simulations ont été comparés avec ceux du l’expérimental, pour les conditions à la fois fixe et en rotation. En général, de bonnes concordances ont été notées.

The aerodynamic drag of simplified car geometry with small span and strongly separated wake can be reduced up 20% by using pulsed jet distributed along the rear window. Results show an enhancement of transversal wake size in the control region, a displacement of the mean positions of vortex wake structures, a decrease of velocities near the rear part and a reduction of vortex structure recirculation in the wake. These modifications produced by the control are analyzed, commented and model based on simple strategy to build efficient and suitable separation control strategy is proposed. [ABSTRACT FROM AUTHOR]

On the April 9 of 2000, a gigantic rapid rock slide-debris avalanche occurred in Bomi, Tibet. Some 280-300 × 10 m of material travelled 10 km within 10 min and dammed the Yigong River, forming a 2.9 × 10 m³ barrier lake. Wind tunnel testing was undertaken to determine the aerodynamic parameters involved, from the initial rock slide-fall to its point of impact. The paper reports the numerical analyses undertaken and discusses the significance of the air-cushion effect. It is concluded that Yigong rapid rock slide-debris avalanche 'flew' in the air for about 12.9 s from its detachment from the source to its collision with the floor of the Zamunong gully at 3,317 m asl. The velocity of the avalanche mass at the point of detachment was some 81.8 m/s and the collision velocity approximately 117 m/s. [ABSTRACT FROM AUTHOR]

Effects of crosswind on a simplified car model with a DES method. This study deals with the crosswind effects on a simplified car model, named the Willy model. This model without sharp corner on the fore body and a square base is more convenient for the analysis of unsteady separations limited on its leeward side and base. The simulations are carried out with the flow solver ISIS-CFD by a DES approach and the results are compared to the experimental data and to the results obtained by a RANSE simulation. The comparisons deal with pressure, total pressure and forces and yawing moment. [ABSTRACT FROM AUTHOR]

The control by blowing techniques of longitudinal vortices originating at the rear pillars of a simplified automobile vehicle are analyzed by an experimental approach on the Ahmed body having a rear window angle of 25°. The experimental measurements are conducted according to stereoscopic Particle Image Velocimetry (Stereo-PIV). The results show that the blowing technique is associated to an increase of vorticity inside the vortex core on the upper part of the rear window and a decrease of vorticity on the lower part of the window. This vorticity drop is related to the onset of a recirculation zone (negative longitudinal velocities) in the vortex core which characterizes the vortex breakdown. The analysis of the azimuthal and longitudinal velocities allows to identify the increase of the Swirl number up to the critical point of vortex breakdown noted for high blowing velocities. [ABSTRACT FROM AUTHOR]

Abstract: Aims: In the present paper main parameters of the discus throw has been performed as function of the wind velocity the release velocity and the release angle. Current knowledge: The performance of the discus throw depends on athlete performance as well as environment. Recently biomechanic researchers worked on the usefulness of the wind during the discus throw. Two theories were revealed: the range of the discus throw can be higher if the throwing was in the same direction of the wind and the second theory suppose that the discus, regarding its aerodynamic profiles, can be considered as airplane wing. To achieve this study, first describe the movement of the discus during the flight taking into account the wind velocity, the initial velocity when the discus is thrown, the release angle and the incline angle of the discus. Equations of the movement has been described for each axis (Ox, Oy) and solved using numerical code (Mathematica 5®) with failure around 5%. The results were presented for angles between 0 and 70° and for speeds, with average performance, 25 m/s, high performance, 27 m/s, and with exceptional performance, 30 m/s, the wind velocity of the environment is supposed equal to 10 m/s and is in the opposite direction of the discus throw. Conclusion: Results show that the height of the throw increase with the release angle and the optimum angle to throw the discus is around 34° for this environment conditions. [Copyright &y& Elsevier]

Abstract: In supersonic flight, Armor Piercing Fin Stabilized Discarding Sabot (APFSDS) projectiles are submitted to a high level of heating and structural loading. We have developed a numerical approach based on 3-D RANS and 2-D coupled aero-heating/conduction computations in order to understand and predict this severe aero-thermal environment. Experimental external aerodynamic and heating load tests have been conducted in a high speed wind tunnel. Computations were compared to experimental results, semi-empirical formulations and evaluations carried out in similar studies elsewhere. A very close agreement was obtained. [Copyright &y& Elsevier]

Abstract: The breakdown of a longitudinal vortex originating from a three-dimensional dihedral body is examined in the perspective of reducing the aerodynamic drag of bluff bodies. The vortex breakdown is induced by a continuous and uniform blowing distributed on the separation line related to the formation and the development of the vortex. The breakdown is characterized by an abrupt disintegration of the vortical core and the appearance of a recirculation zone. Numerical results obtained with and without blowing show the crucial impact of the Swirl parameter on the vortex breakdown. Drag reductions close to 6% are found. To cite this article: B. Lehugeur et al., C. R. Mecanique 334 (2006). [Copyright &y& Elsevier]

Abstract: Until recently, wind tunnel measurements were made solely by pressure taps. But now an optical measurement method has been introduced and is replacing the usual instrumentation, at least for transonic wind tunnels: Pressure-Sensitive Paint, or PSP, which is a method generating an image of the pressure on the surface. The enthusiasm for this technique is prompted by the considerable savings it offers in terms of model instrumentation cost and model construction time, while the wealth of information that can be extracted from the images makes it a preferential investigation tool for complex flows. This article presents the basics of PSP and the way it is used. It is relatively simple to use, in fact, but requires many precautions if a high level of accuracy is desired. The software aspects are important, especially for tests conducted in an industrial context. The various elements of a PSP system are illustrated here with an example of application in low-speed testing. Advanced topics as model deformation are also discussed. [Copyright &y& Elsevier]

Abstract: This paper is a review on the dynamics of vortices in fluids which get involved in aircraft wakes. Basic notions useful to appraise their dynamics are: inertial waves, 3D instabilities due to vortex interaction, vortex merging, vortex breakdown and turbulence. Each one of these topics is illustrated by means of experimental or numerical results. To cite this article: L. Jacquin et al., C. R. Physique 6 (2005). [Copyright &y& Elsevier]

Abstract: Flow momentum that is deflected in a persistent way by a wing, or by another flow, becomes organised in coherent and energetic vortex structures. This phenomenon is briefly introduced here by comparison with other phenomena such as the production of vortices by impulsive forces (e.g. during animal flight), or the production of turbulence by jets. These considerations aim at underlining the fundamental nature of this strange mechanism, which is usually hidden behind engineering models produced by aerodynamic science. The control of these mechanisms, for applications to the safety of the airplanes for example, opens a vast multidisciplinary field of research. To cite this article: L. Jacquin, C. R. Physique 6 (2005). [Copyright &y& Elsevier]

Copyright of Annals of Telecommunications is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)