CNRS Institute of Fluid Mechanics of Toulouse
Toulouse, France
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Lorthois S.,CNRS Institute of Fluid Mechanics of Toulouse | Cassot F.,French Institute of Health and Medical Research | Lauwers F.,French Institute of Health and Medical Research
NeuroImage | Year: 2011

In a companion paper (Lorthois et al., Neuroimage, in press), we perform the first simulations of blood flow in an anatomically accurate large human intra-cortical vascular network (~ 10000 segments), using a 1D non-linear model taking into account the complex rheological properties of blood flow in microcirculation. This model predicts blood pressure, blood flow and hematocrit distributions, volumes of functional vascular territories, regional flow at voxel and network scales, etc. Using the same approach, we study flow reorganizations induced by global arteriolar vasodilations (an isometabolic global increase in cerebral blood flow). For small to moderate global vasodilations, the relationship between changes in volume and changes in flow is in close agreement with Grubb's law, providing a quantitative tool for studying the variations of its exponent with underlying vascular architecture. A significant correlation between blood flow and vascular structure at the voxel scale, practically unchanged with respect to baseline, is demonstrated. Furthermore, the effects of localized arteriolar vasodilations, representative of a local increase in metabolic demand, are analyzed. In particular, localized vasodilations induce flow changes, including vascular steal, in the neighboring arteriolar trunks at small distances (<300μm), while their influence in the neighboring veins is much larger (about 1 mm), which provides an estimate of the vascular point spread function. More generally, for the first time, the hemodynamic component of various functional neuroimaging techniques has been isolated from metabolic and neuronal components, and a direct relationship with several known characteristics of the BOLD signal has been demonstrated. © 2010 Elsevier Inc.

Sennoune M.,French National Center for Scientific Research | Salvador S.,French National Center for Scientific Research | Quintard M.,CNRS Institute of Fluid Mechanics of Toulouse
Combustion and Flame | Year: 2011

One technique used to recover oil from ground oil shale, or to burn oil shale semicoke, consists of propagating a smoldering front through a packed bed. One drawback of this technique is that the mineral structure of the shale is decarbonated due to the high temperature of the front. This phenomenon causes 70% of the CO2 emissions released during such processes. The remaining 30% result from the fixed carbon oxidation. With the aim of decreasing the front temperature and thus avoiding decarbonation at the front passage, the impact of two parameters was experimentally tested in this work: first, increasing the amount of carbonates, as they may play the role of a heat sink, and second, decreasing the amount of fixed carbon in the medium. It is shown that increasing the amount of carbonates can only decrease the front temperature to 800°C but not lower, which is still too high to avoid decarbonation. On the other hand, the front temperature can be decreased enough for decarbonation to be almost completely avoided by reducing the amount of fixed carbon. At the low temperatures reached, almost all the fixed carbon is oxidized, but not all the oxygen transported in the air is consumed by the chemical front. The velocity of the front is consequently decreased. © 2011 The Combustion Institute.

Ceballos L.,National Polytechnic Institute of Toulouse | Ceballos L.,CNRS Institute of Fluid Mechanics of Toulouse | Prat M.,National Polytechnic Institute of Toulouse | Prat M.,CNRS Institute of Fluid Mechanics of Toulouse
Journal of Power Sources | Year: 2010

Liquid water transport in the diffusion porous layers of polymer electrolyte membrane fuel cells (PEMFC) is analyzed as a process of quasi-static invasion from multiple interfacial injection sources. From pore network simulations based on a new version of the invasion percolation algorithm it is shown that a porous layer acts as a two-phase filter: the number of breakthrough points is significantly lower that the number of injection points owing to the merging of liquid paths within the porous layer. The number of breakthrough points at the gas diffusion layer/gas channel interface obtained with this model is consistent with the available experimental observations. © 2009 Elsevier B.V. All rights reserved.

Veran-Tissoires S.,National Polytechnic Institute of Toulouse | Veran-Tissoires S.,CNRS Institute of Fluid Mechanics of Toulouse | Marcoux M.,National Polytechnic Institute of Toulouse | Marcoux M.,CNRS Institute of Fluid Mechanics of Toulouse | And 2 more authors.
Physical Review Letters | Year: 2012

Efflorescence refers to crystallized salt structures that form at the surface of a porous medium. The challenge is to understand why these structures do not form everywhere at the surface of the porous medium but at some specific locations and why there exists an exclusion distance around an efflorescence where no new efflorescence forms. These are explained from a visualization experiment, pore-network simulations and a simple efflorescence growth model. © 2012 American Physical Society.

Wang Y.,University of Notre Dame | Plouraboue F.,CNRS Institute of Fluid Mechanics of Toulouse | Chang H.-C.,University of Notre Dame
Optics Express | Year: 2013

We propose an analytical theory which predicts that Converging Plasmon Resonance (CPR) at conical nanotips exhibits a red-shifted and continuous band of resonant frequencies and suggests potential application of conical nanotips in various fields, such as plasmonic solar cells, photothermal therapy, tip-enhanced Raman and other spectroscopies. The CPR modes exhibit superior confinement and ten times broader scattering bandwidth over the entire solar spectrum than smooth nano-structures. The theory also explicitly connects the optimal angles and resonant optical frequencies to the material permittivities, with a specific optimum half angle that depends only on the real permittivity for high-permittivity and low-loss materials. © 2013 Optical Society of America.

Thual O.,CNRS Institute of Fluid Mechanics of Toulouse
Journal of Fluid Mechanics | Year: 2013

Hydraulic jumps, roll waves or bores in open channel flows are often treated as singularities by hydraulicians while slowly varying shallow water flows are described by continuous solutions of the Saint-Venant equations. Richard & Gavrilyuk (J. Fluid Mech., vol. 725, 2013, pp. 492-521) have enriched this model by introducing an equation for roller vorticity in a very elegant manner. This new model matches several experimental results that have resisted theoretical approaches for decades. This is the case of the roller of a stationary hydraulic jump as well as the oscillatory instability that the jump encounters when the Froude number is increased. The universality of their approach as well as its convincing comparisons with experimental results open the way for significant progress in the modelling of open channel flows. © 2013 Cambridge University Press.

Ceballos L.,CNRS Institute of Fluid Mechanics of Toulouse | Prat M.,CNRS Institute of Fluid Mechanics of Toulouse
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2013

We study numerically the process of quasistatic invasion of a fluid in thin porous layers from multiple inlet injection sources focusing on the effect of trapping or mixed wettability, that is, when hydrophobic and hydrophilic pores coexist in the system. Two flow scenarios are considered. In the first one, referred to as the sequential scenario, the injection bonds at the inlet are activated one after the other. In the second one, referred to as the kinetic scenario, the injection bonds at the inlet are activated simultaneously. In contrast with the case of purely hydrophobic systems with no trapping, studied in a previous work, it is shown that the invasion pattern and the breakthrough point statistics at the end of the displacement depend on the flow scenario when trapping or mixed wettability effects are taken into account. The transport properties of the defending phase are also studied and it is shown that a one-to-one relationship between the overall diffusive conductance and the mean saturation cannot be expected in a thin system. In contrast with thick systems, the diffusive conductance also depends on the thickness when the system is thin. After consideration of various generic aspects characterizing thin porous systems, the main results are briefly discussed in relation with the water management problem in proton exchange membrane fuel cells. © 2013 American Physical Society.

Prat M.,CNRS Institute of Fluid Mechanics of Toulouse
Chemical Engineering and Technology | Year: 2011

Pore network modeling is now a well-established and successful technique for understanding and predicting a wide range of drying features. This paper presents an overview of recent works with special focus on the effect of liquid films and wettability. The capability of pore network models is also illustrated through a discussion of the classical drying curve of capillary porous media, which is divided into three main periods. Some open problems and future prospects are discussed. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Dupont J.-B.,National Polytechnic Institute of Toulouse | Dupont J.-B.,CNRS Institute of Fluid Mechanics of Toulouse | Legendre D.,National Polytechnic Institute of Toulouse | Legendre D.,CNRS Institute of Fluid Mechanics of Toulouse
Journal of Computational Physics | Year: 2010

A numerical "macroscopic-scale" method for static (including hysteresis) and moving contact lines for partially wetting liquids is presented. The numerical method is based on the implementation of a "sub-grid" description of the contact line that consists in imposing the apparent angle for static and moving contact lines. The numerical simulations are validated against several well controlled bi-dimensional situations: the equilibrium shape of a drop released on a hydrophobic or hydrophilic wall, the axisymmetric spreading of a drop for a partially wetting liquid, the migration of a drop placed on a inclined wall and submitted to a Couette or Poiseuille flow. © 2009 Elsevier Inc. All rights reserved.

Magnaudet J.,CNRS Institute of Fluid Mechanics of Toulouse
Journal of Fluid Mechanics | Year: 2011

Several forms of a theorem providing general expressions for the force and torque acting on a rigid body of arbitrary shape moving in an inhomogeneous incompressible flow at arbitrary Reynolds number are derived. Inhomogeneity arises because of the presence of a wall that partially or entirely bounds the fluid domain and/or a non-uniform carrying flow. This theorem, which stems directly from Navier-Stokes equations and parallels the well-known Lorentz reciprocal theorem extensively employed in low-Reynolds-number hydrodynamics, makes use of auxiliary solenoidal irrotational velocity fields and extends results previously derived by Quartapelle & Napolitano (AIAA J., vol. 21, 1983, pp. 911-913) and Howe (Q. J. Mech. Appl. Maths, vol. 48, 1995, pp. 401-426) in the case of an unbounded flow domain and a fluid at rest at infinity. As the orientation of the auxiliary velocity may be chosen arbitrarily, any component of the force and torque can be evaluated, irrespective of its orientation with respect to the relative velocity between the body and fluid. Three main forms of the theorem are successively derived. The first of these, given in (2.19), is suitable for a body moving in a fluid at rest in the presence of a wall. The most general form (3.6) extends it to the general situation of a body moving in an arbitrary non-uniform flow. Specific attention is then paid to the case of an underlying time-dependent linear flow. Specialized forms of the theorem are provided in this situation for simplified body shapes and flow conditions, in (3.14) and (3.15), making explicit the various couplings between the body's translation and rotation and the strain rate and vorticity of the carrying flow. The physical meaning of the various contributions to the force and torque and the way in which the present predictions reduce to those provided by available approaches, especially in the inviscid limit, are discussed. Some applications to high-Reynolds-number bubble dynamics, which provide several apparently new predictions, are also presented. © 2011 Cambridge University Press.

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