Energy spectra in bubbly turbulence

Revue de l'OFCE, 1994

La transition entre la turbulence tridimensionnelle et la turbulence quasi-bidimensionnelle sous l'effet d'une rotation d'ensemble estétudiée expérimentalement. Uń ecoulement turbulent est généré par la translation d'une grille dans une cuve d'eau en rotation, et un système de vélocimétrie par images de particules est utilisé pour mesurer les champs de vitesse instantanés dans un plan perpendiculaireà l'axe de rotation. Les spectres d'énergie des fluctuations spatiales de vitesse présentent une loi de puissance, E(k) ∼ k −n , dont l'exposant n augmente continûment de n 5/3 vers n 2,3 pendant le déclin,à mesure que diminue le nombre de Rossby. Le coefficient d'asymétrie des dérivées de vitesse diminue avec Ro ω , reflétant l'inhibition des transferts d'énergie par la rotation d'ensemble, tandis qu'une cascade inverse d'énergie se développe aux grandeséchelles.

Comptes Rendus De L Academie Des Sciences Serie Ii Fascicule B-mecanique Physique Astronomie, 1998

La Houille Blanche, 1996

2005

The two-phase flows involve interfacial interactions which modify significantly the structure of the mean and fluctuant flow fields. The design of the two-fluid models adapted to industrial flows requires the taking into account of the effect of these interactions in the closure relations adopted. The work developed in this thesis concerns the development of first order two-fluid models deduced by reduction of second order closures. The adopted reasoning, based on the principle of decomposition of the Reynolds stress tensor into two statistically independent contributions turbulent and pseudo-turbulent parts, allows to preserve the physical contents of the second order relations closure. Analysis of the turbulence structure in two basic flows : homogeneous bubbly flows uniform and with a constant shear allows to deduce a formulation of the two-phase turbulent viscosity involving the characteristic scales of bubbly turbulence, as well as an analytical description of modification of the homogeneous turbulence structure induced by the bubbles presence. The eulerian two-fluid model was then generalized with the case of the inhomogeneous flows with low void fractions. The numerical results obtained by the application of this model integrated in the computer code MELODIF in the case of free sheared turbulent bubbly flow of wake showed a satisfactory agreement with the experimental data and made it possible to analyze the modification of the characteristic scales of such flow by the interfacial interactions. The twofluid first order model is generalized finally with the case of high void fractions bubbly flows where the hydrodynamic interactions between the bubbles are not negligible any more.

La Houille …, 1996

Le régime d'écoulement diphasique à bulles se rencontre dans de nombreuses applications industrielles et a été étudié intensivement durant ces dernières années, Cepen-dant, la compréhension des phénomènes physiques impli-qués dans ce régime est encore trop limitée pour ...

ETC, 2003

Archaeological and Anthropological Sciences, 2024

V. Occari - H. Möller - C. Fenwick - P. Quinn - I. C. Freestone - M. Chaouali - P. von Rummel. Abstract: Ifriqiya (roughly Tunisia and eastern Algeria) is believed to have played a significant role in the diffusion of ceramic glazed technologies into other regions of the Western Mediterranean. However, due to limited analysis on North African glazed ceramics, its role in technology transfer remains poorly understood. This paper uses SEM-EDS and petrographic analyses to understand the technology employed in the production of Tunisian ceramics through the study of 30 polychrome glazed ceramics from a medieval settlement at the site of Chimtou (ancient Simitthus), Tunisia, dated to the late ninth-twelfth century. The results show that these are lead-rich glazes with varying contents of alkalis, coloured with copper, iron and manganese oxide and applied over a calcareous body. Opaque glazes were obtained using cassiterite crystals as opacifier or by adding crushed quartz. The use of lead stannate as a colourant and opacifier in one light yellow glaze raises questions about the mechanisms of introduction of tin opacification technology in North Africa. Scrap metal seems to have been used as a source of lead for the glazes; while iron slag was probably used as a source of iron to colour the glaze in one sample, pointing to a cross-craft interaction between glazemaking and metallurgy.

The global nephrology community recognises the need for a cohesive plan to address the problem of chronic kidney disease (CKD). In July, 2016, the International Society of Nephrology hosted a CKD summit of more than 85 people with diverse expertise and professional backgrounds from around the globe. The purpose was to identify and prioritise key activities for the next 5–10 years in the domains of clinical care, research, and advocacy and to create an action plan and performance framework based on ten themes: strengthen CKD surveillance; tackle major risk factors for CKD; reduce acute kidney injury—a special risk factor for CKD; enhance understanding of the genetic causes of CKD; establish better diagnostic methods in CKD; improve understanding of the natural course of CKD; assess and implement established treatment options in patients with CKD; improve management of symptoms and complications of CKD; develop novel therapeutic interventions to slow CKD progression and reduce CKD complications; and increase the quantity and quality of clinical trials in CKD. Each group produced a prioritised list of goals, activities, and a set of key deliverable objectives for each of the themes. The intended users of this action plan are clinicians, patients, scientists, industry partners, governments, and advocacy organisations. Implementation of this integrated comprehensive plan will benefit people who are at risk for or affected by CKD worldwide.