Tourbillon de turbulence

Résumé

vignette|upright=0.75|Allées de Karman autour de Madère et des îles Canaries vignette|upright=0.75|Les courants océaniques de Oya shivo et Kuroshio se rencontrent et donnent un tourbillon de turbulence visible par la concentration du phytoplancton dans le vortex. Un tourbillon de turbulence est un élément d'une masse fluide turbulente qui a une certaine individualité et une certaine vie qui lui sont propres. Il peut être causé par un obstacle dans le flot créant un contre-courant, par une différence de densité entre deux sections du fluide ou par la rencontre de deux fluides. Les tourbillons de turbulence sont un élément courant en météorologie, en hydrologie et en océanographie. Principe Un fluide homogène se déplaçant à une vitesse constante est dit en écoulement laminaire et toutes ses particules restent stationnaires par rapport aux autres. Lorsqu'un tel fluide rencontre un obstacle, il doit le contourner, ce qui crée une vitesse nulle en aval. Par conservation du mouv

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https://fr.wikipedia.org/wiki/Tourbillon_de_turbulence

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Dynamic modeling and simulation of a pipeline used for transportation of a fluid near the saturation

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A new district energy network has been developed by using CO2 as a heat transfer fluid. Only two pipes are required by the network, thus allowing the recovery of waste heat from the cooling users to be valorized by the heating users. Understanding and predicting the dynamics as well as identifying control methods and strategies is one of the key issues for the development of such a CO2 network that would operate in a safe, reliable and energy efficient manner. To assess the technical feasibility and address the safety problems, a physical-based model was developed to describe the fluid dynamics of CO2 pipelines used for transportation of a fluid near the saturation. Dynamic simulations were carried out to investigate pressure and flow fluctuation during transient flow and under changes of external perturbations. It shows that the system was able to response all these perturbations although the corresponding pressure wave propagates along the pipe.

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Geometric, variational discretization of continuum theories

Mathieu Desbrun

This study derives geometric, variational discretization of continuum theories arising in fluid dynamics, magnetohydrodynamics (MHD), and the dynamics of complex fluids. A central role in these discretizations is played by the geometric formulation of fluid dynamics, which views solutions to the governing equations for perfect fluid flow as geodesics on the group of volume-preserving diffeomorphisms of the fluid domain. Inspired by this framework, we construct a finite-dimensional approximation to the diffeomorphism group and its Lie algebra, thereby permitting a variational temporal discretization of geodesics on the spatially discretized diffeomorphism group. The extension to MHD and complex fluid flow is then made through an appeal to the theory of Euler-Poincare systems with advection, which provides a generalization of the variational formulation of ideal fluid flow to fluids with one or more advected parameters. Upon deriving a family of structured integrators for these systems, we test their performance via a numerical implementation of the update schemes on a cartesian grid. Among the hallmarks of these new numerical methods are exact preservation of momenta arising from symmetries, automatic satisfaction of solenoidal constraints on vector fields, good long-term energy behavior, robustness with respect to the spatial and temporal resolution of the discretization, and applicability to irregular meshes. (C) 2011 Elsevier B.V. All rights reserved.

2011

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