Experimental determination of the growth rate of Richtmyer-Meshkov induced turbulent mixing after reshock

The time evolution of the width of the turbulent mixing zone arising from the late development of Richtmyer-Meshkov instability is investigated in this work. This is achieved by means of the analysis of time-resolved Schlieren images obtained with a given set of shock-tube experiments. The post-reshock growth rate of the mixing zone width is found to be nearly insensitive to the development state of the mixing at the time of reshock

Study of the turbulent mixing zone induced by the Richtmyer-Meshkov instability using Laser Doppler Velocimetry and Schlieren visualizations

An experimental study of the compressible mixing generated by the Richtmyer-Meshkov instability (RMI) is carried out in a vertical shock tube by means of two-components Laser Doppler Velocimetry (2C-LDV) measurements and Time-resolved Schlieren visualizations. An attempt is made to quantify the RMI-induced air/sulphurhexafluoride (SF6) mixing by measuring turbulence levels inside the mixing zone at a given stage of its development and by extracting the growth rate of the mixing zone from the Schlieren images

« In a Pomp of Colour » : couleur et modernité chez George Moore

Soucieux comme tous les Esthètes de débarrasser l’art anglais des scories narratives dont il était encore largement prisonnier à la fin du xixe siècle, George Moore choisit dans sa critique d’art de mettre en avant la notion de couleur, que ce soit pour déplorer les teintes “sales” de certains artistes ou pour saluer les nuances subtiles des autres. En montrant que les plus grands peintres ont toujours privilégié les valeurs chromatiques par rapport à l’anecdote, et en faisant coïncider le déclin de l’art avec la prédominance du sujet, Moore révise la hiérarchie des artistes victoriens : le mépris que lui inspirent les membres de la Royal Academy trouve ainsi un fondement théorique, la peinture d’histoire est vouée aux oubliettes de l’histoire et Whistler, créateur des harmonies colorées, est porté aux nues. Pourtant, George Moore s’oppose au divisionnisme, dont il juge les principes aberrants, prouvant ainsi son attachement envers une conception “classique” de la couleur, contre la “couleur locale”, ce vice impuni, au profit d’une palette plus “mélodieuse”.Like the Aesthetes, George Moore wanted to get rid of the narrative constraints which still lay heavily on painting in the late nineteenth century. In his art criticism, he decided to promote the notion of colour, either to lament the “dirty” tints of some painters or to salute the subtle hues of some others. By showing that great masters had always preferred chromatic values to anecdote, and by equating the decline of art with the predominance of the subject, Moore revised the hierarchy of Victorian artists and gave a theoretical basis to his contempt for Royal Academicians. History painting was doomed to oblivion and Whistler, the creator of colour harmonies, was hailed by him as the supreme artist. However, Moore was hostile to divisionism, whose principles he judged absurd, thus proving his attachment for a “classical” conception of colour, against the sin of “local colour”, in favour of a more “melodious” palette

Numerical and experimental investigations of buffet on a diamond airfoil designed for space launcher applications

Purpose – The development of reusable space launchers requires a comprehensive knowledge of transonic flow effects on the launcher structure, such as buffet. Indeed, the mechanical integrity of the launcher can be compromised by shock wave/boundary layer interactions, that induce lateral forces responsible for plunging and pitching moments. Design/methodology/approach – This paper aims to report numerical and experimental investigations on the aerodynamic and aeroelastic behavior of a diamond airfoil, designed for microsatellite-dedicated launchers, with a particular interest for the fluid/structure interaction during buffeting. Experimental investigations based on Schlieren visualizations are conducted in a transonic wind tunnel and are then compared with numerical predictions based on unsteady Reynolds averaged Navier–Stokes and large eddy simulation (LES) approaches. The effect of buffeting on the structure is finally studied by solving the equation of the dynamics. Findings – Buffeting is both experimentally and numerically revealed. Experiments highlight 3D oscillations of the shock wave in the manner of a wind-flapping flag. LES computations identify a lambda- shaped shock wave foot width oscillations, which noticeably impact aerodynamic loads. At last, the experiments highlight the chaotic behavior of the shock wave as it shifts from an oscillatory periodic to an erratic 3D flapping state. Fluid structure computations show that the aerodynamic response of the airfoil tends to damp the structural vibrations and to mitigate the effect of buffeting. Originality/value – While buffeting has been extensively studied for classical supercritical profiles, this study focuses on diamond airfoils. Moreover, a fluid structure computation has been conducted to point out the effect of buffeting

Fluid-structure interaction between a composite aileron and a turbulent flow at transonic conditions

This work reports some numerical and experimental investigations about the aerodynamic and aeroelastic behavior of a diamond aileron for a launcher dedicated to microsatellites. This work focuses mainly on the flow at transonic conditions with an emphasis on the buffet phenomenon. Indeed, the mechanical integrity of the launcher is largely compromised at transonic regime due to such shock/boundary layer interaction, that induces forces responsible for plunging and pitching moment that can damage the structure. An experimental campaign has been conducted, based on Schlieren visualizations. The experimental data are then compared with numerical predictions obtained with unsteady RANS and LES. The final objective is the analysis of buffeting impact on the composite material of the aileron

Numerical and experimental investigations of buffet on a diamond airfoil designed for space launchers applications

The capability to reuse space launchers for new missions requires to better understand flow phenomena in the transonic regime, such as buffet, and its interaction with the structure. Indeed, the mechanical integrity of the launcher can be compromised by shock/boundary layer interactions, that induce lateral forces responsible for plunging and pitching moments. This work reports some numerical and experimental investigations about the aerodynamic and aeroelastic behavior of a diamond airfoil, designed for microsatellite-dedicated launchers, with a particular interest for the fluid/structure interaction during buffeting. Experiments have been conducted, based on Schlieren visualizations, and compared with numerical predictions obtained with unsteady RANS and Large-Eddy Simulation. Finally, the effect of buffeting on the composite aileron is studied by solving the equation of the dynamics, showing that the aerodynamic response of the airfoil tends to damp the structural displacement, and thus limit the effect of buffeting

RETRATO SIN IDENTIFICAR [Material gráfico]

Copia digital. Madrid : Ministerio de Educación, Cultura y Deporte, 201

La troponine T ultrasensible : un nouvel outil diagnostic pour le médecin sportif?

peer reviewedIntroduction : Le risque d’accidents cardiaques ou de mort subite après effort physique intense est bien connu. Ces évènements indésirables se produisent souvent chez des sujets présentant une maladie coronarienne asymptomatique et ignorée. Néanmoins, vu ce risque, l’American Heart Association recommande de réaliser un screening cardiovasculaire chez les athlètes de tout âge. Dans cette optique, le dosage de marqueurs cardiaques de nouvelle génération, plus sensibles, comme la troponine T ultrasensible (hsTnT) peut certainement apporter des informations très intéressantes par la détection de dommages myocardiques mêmes mineurs. Matériels et méthodes : Des 20 sujets masculins volontaires âgés de 22.36±2.02 années, sédentaires, 8 ont dû être exclus (abandon, malaise à l’effort...). La VO2max a été préalablement déterminée lors d’un test à l’effort sur cycloergomètre une semaine avant le test afin de ne pas interférer avec les résultats de l’effort physique intense (EPI) pour lequel les sujets ont couru sur tapis roulant durant 1 heure à 75% de la VO2max. Quatre échantillons sanguins de 5 ml (tube hépariné-lithium) ont été prélevés : juste avant (T1), directement après (T2), 4 heures après (T3) et 24 heures après l’EPI (T4). Le dosage de hsTnT (Modular de Roche Diagnostic®) est réalisé sur du plasma par une technique d’électrocheminiluminescence. Résultats : Une augmentation statistiquement significative des résultats à T3 (p<0.01) est observée. L’élévation de la hsTnT est progressive pour atteindre un pic maximum à T3 et revenir dans les normes à T4. Le seuil critique de 0.03 ng/mL a été retenu et 75% des sujets présentent un taux supérieur à ce dernier à T3 (moyenne : 0.053 ng/mL), alors que 100% des sujets se trouvent en dessous de ce seuil à T1 (0.0041 ng/mL). Discussion - Conclusions : Ces résultats, extrêmement intéressants, suggèrent que la libération de hsTnT serait due soit à un processus physiologique de remodelage, soit à un processus irréversible de lésions au niveau des cardiomyocytes (nécrose). Il est également possible que cette élévation des troponines soit due à une libération à partir du pool cytosolique mais aussi elle peut être la conséquence de dommages membranaires potentiellement induits par le stress oxydatif. A l’issue de cette étude, nous démontrons que la hsTnT peut être un nouvel outil diagnostic dans le domaine de la cardiologie du sport

LDV measurements in turbulent gaseous mixing induced by the Richtmyer-Meshkov instability: statistical convergence issues and turbulence quantification

A statistical characterization of the turbulent flow produced in a vertical shock tube dedicated to the study of the Richtmyer-Meshkov instability (RMI) is carried out using Laser Doppler Velocimetry (LDV), time-resolved Schlieren images and pressure histories. The time evolution of the phase-averaged velocity field and the fluctuating velocity levels produced behind the shock wave are first investigated for different configurations of a pure air, homogeneous medium. This allows us to determine the background turbulence of the experimental apparatus. Second, the RMI-induced turbulent Air/SF6 mixing zone (TMZ) is studied both in its early stage of development and after its interaction with a reflected shock wave (reshock phenomenon). Here the gaseous interface is initially produced by a thin nitrocellulosic membrane trapped between two grids. One of the most consistent issue regarding such a process is the generation of a large number of fragments when the incident shock wave crosses the interface. These fragments are likely to corrupt the optical measurements and to interact with the flow. This work seeks to clarify the influence of these fragments on the statistical determination of the velocity field. In particular it is shown that statistical convergence cannot be achieved when the fragments are crossing the LDV measurement volume, even if a significant number of identical experiments are superimposed. Some specific locations for the LDV measurements are however identified to be more favourable than others in the Air/SF6 mixing configuration. This finally allows us to quantify the surplus of turbulence induced by the reshock phenomenon