"Barber pole turbulence" in large aspect ratio Taylor-Couette flow

Investigations of counter-rotating Taylor-Couette flow (TCF) in the narrow gap limit are conducted in a very large aspect ratio apparatus. The phase diagram is presented and compared to that obtained by Andereck et al. The spiral turbulence regime is studied by varying both internal and external Reynolds numbers. Spiral turbulence is shown to emerge from the fully turbulent regime via a continuous transition appearing first as a modulated turbulent state, which eventually relaxes locally to the laminar flow. The connection with the intermittent regimes of the plane Couette flow (pCf) is discussed

On the decay of turbulence in plane Couette flow

The decay of turbulent and laminar oblique bands in the lower transitional range of plane Couette flow is studied by means of direct numerical simulations of the Navier--Stokes equations. We consider systems that are extended enough for several bands to exist, thanks to mild wall-normal under-resolution considered as a consistent and well-validated modelling strategy. We point out a two-stage process involving the rupture of a band followed by a slow regression of the fragments left. Previous approaches to turbulence decay in wall-bounded flows making use of the chaotic transient paradigm are reinterpreted within a spatiotemporal perspective in terms of large deviations of an underlying stochastic process.Comment: ETC13 Conference Proceedings, 6 pages, 5 figure

Huysmans pornographe

La question de l’écriture pornographique est d’autant plus intéressante chez Huysmans que, au-delà du témoignage qu’elle offre quant à la place de l’érotisme dans la littérature de la fin du dix-neuvième siècle, elle est également un critérium inattendu de l’unité de l’œuvre. En effet, si la pornographie est au cœur des pratiques sexuelles et littéraires huysmansiennes, c’est moins sa visibilité explicite qui est à souligner que sa surprenante discrétion dans les romans naturalistes qui ont pourtant fait la réputation sulfureuse de l’auteur. Tout au contraire, ce sont les poèmes du Drageoir aux épices qui donnent les portraits de femmes annonciateurs de ce que l’on retrouvera sous la plume de l’auteur d’À rebours, ambivalents et marqués par le caractère antithétique de l’amour sadique, par la même crudité pornographique que celle des fleurs de Des Esseintes ou le rêve de la Syphilis. Le monde onirique ouvre alors l’espace d’une spiritualisation de l’ordure qui est celui du sadisme de Félicien Rops ou de Gilles de Rais, qui transfigure l’écriture du sexe en écriture de la monstruosité et les noces de la chair en noces spirituelles. Mais le trait le plus marquant est certainement celui de la réflexion sur l’essence même de l’écriture que la question permet à l’auteur converti. Après s’être plu à provoquer le bourgeois, Huysmans s’emploie en effet à scandaliser les bigots par le même langage, faisant basculer le point d’équilibre de sa pornographie de pornê à graphê.

Transient growth in Taylor-Couette flow

Transient growth due to non-normality is investigated for the Taylor-Couette problem with counter-rotating cylinders as a function of aspect ratio eta and Reynolds number Re. For all Re < 500, transient growth is enhanced by curvature, i.e. is greater for eta < 1 than for eta = 1, the plane Couette limit. For fixed Re < 130 it is found that the greatest transient growth is achieved for eta between the Taylor-Couette linear stability boundary, if it exists, and one, while for Re > 130 the greatest transient growth is achieved for eta on the linear stability boundary. Transient growth is shown to be approximately 20% higher near the linear stability boundary at Re = 310, eta = 0.986 than at Re = 310, eta = 1, near the threshold observed for transition in plane Couette flow. The energy in the optimal inputs is primarily meridional; that in the optimal outputs is primarily azimuthal. Pseudospectra are calculated for two contrasting cases. For large curvature, eta = 0.5, the pseudospectra adhere more closely to the spectrum than in a narrow gap case, eta = 0.99

Surface freshwater storage variations in the Orinoco floodplains using multi-satellite observations

Variations in surface water extent and storage are poorly characterized from regional to global scales. In this study, a multi-satellite approach is proposed to estimate the water stored in the floodplains of the Orinoco Basin at a monthly time-scale using remotely-sensed observations of surface water from the Global Inundation Extent Multi-Satellite (GIEMS) and stages from Envisat radar altimetry. Surface water storage variations over 2003-2007 exhibit large interannual variability and a strong seasonal signal, peaking during summer, and associated with the flood pulse. The volume of surface water storage in the Orinoco Basin was highly correlated with the river discharge at Ciudad Bolivar (R = 0.95), the closest station to the mouth where discharge was estimated, although discharge lagged one month behind storage. The correlation remained high (R = 0.73) after removing seasonal effects. Mean annual variations in surface water volume represented similar to 170 km(3), contributing to similar to 45% of the Gravity Recovery and Climate Experiment (GRACE)-derived total water storage variations and representing similar to 13% of the total volume of water that flowed out of the Orinoco Basin to the Atlantic Ocean