Benchmark solution for a three-dimensional mixed convection flow - Part 1: reference solutions

International audienceAbstract A solution to a benchmark problem for a three-dimensional mixed convection flow in a horizontal rectangular channel heated from below and cooled from above (Poiseuille-Rayleigh-Bénard flow) is proposed. This flow is a steady thermoconvective longitudinal roll flow in a large aspect ratio channel at moderate Reynolds and Rayleigh numbers (Re=50, Ra=5000) and Prandtl number Pr=0.7. The model is based on the Navier-Stokes equations with Boussinesq approximation. We propose reference solutions resulting from computations on large grids, Richardson extrapolation (RE) and cubic spline interpolations. The solutions obtained with one finite difference, one finite volume and two finite element codes are in good agreement and reference values for the flow and thermal fields and the heat and momentum fluxes are given with 4 to 5 significant digits

Towards an integrative, eco-evolutionary understanding of ecological novelty: studying and communicating interlinked effects of global change

Global change has complex eco-evolutionary consequences for organisms and ecosystems, but related concepts (e.g., novel ecosystems) do not cover their full range. Here we propose an umbrella concept of “ecological novelty” comprising (1) a site-specific and (2) an organism-centered, eco-evolutionary perspective. Under this umbrella, complementary options for studying and communicating effects of global change on organisms, ecosystems, and landscapes can be included in a toolbox. This allows researchers to address ecological novelty from different perspectives, e.g., by defining it based on (a) categorical or continuous measures, (b) reference conditions related to sites or organisms, and (c) types of human activities. We suggest striving for a descriptive, non-normative usage of the term “ecological novelty” in science. Normative evaluations and decisions about conservation policies or management are important, but require additional societal processes and engagement with multiple stakeholders

Méthodes d’éléments finis de Trio_U stabilité et expériences numériques

National audienceDans cette présentation, on étudie le comportement des méthodes d’éléments finis disponibles dans Trio_U du point de vue de la problématique des vitesses parasites. On propose également deux extensions a ces méthodes en vue de gagner en coût calcul et d'autoriser d'autres formes géométriques pour les éléments

A manufactured solution for a steady capillary free surface flow governed by the Navier-Stokes equations

International audienc

A manufactured solution for a steady capillary free surface flow governed by the Navier-Stokes equations

International audienc

Vers une solution numérique de référence pour un écoulement 3D de convection mixte : démarche et résultats

National audienceNous présentons dans cette communication la démarche que nous avons adoptée pour conduire un exercice de comparaison de codes de calculs (benchmark) sur une configuration d'écoulement 3D de convection mixte, ainsi que la synthèse des résultats que nous avons obtenus. L'objectif de cette action vise à proposer une première solution numérique tridimensionnelle de référence sur ce type de configuration afin de permettre, une fois celle-ci admise et reconnue par la communauté, de valider des codes de calculs

A CFD benchmark study with an analysis of Richardson Extrapolation in the presence of a singularity

Abstract # V&V2012-607

Verification of a CFD benchmark solution of transient low Mach number flows with Richardson extrapolation procedure

Abstract # V&V2012-6072International audienc

Benchmark Solution for a Three-Dimensional Mixed-Convection Flow, Part 2: Analysis of Richardson Extrapolation in the Presence of a Singularity

Abstract A reference solution to a benchmark problem for a 3D mixed convection flow in a horizontal rectangular channel differentially heated (Poiseuille-Rayleigh-Bénard flow) has been proposed in "Part 1: reference solution" of the present paper [Num. Heat Trans. A, vol.?, pp.?-? (2011)]. Since mixed Dirichlet and Neumann thermal boundary conditions are used on the horizontal walls of the channel, a temperature gradient discontinuity is generated. The aim of this paper is to analyze the consequences of this singularity on Richardson extrapolation (RE) of the numerical solutions. The convergence orders of the used numerical methods (finite difference, finite volume, finite element), observed from RE of local and integral quantities are discussed with an emphasis on singularity influence. With the grids used, it is shown that RE can increase the accuracy of the discrete solutions, preferentially with the discretization methods of low space accuracy order, but only in some part of the channel and for a restricted range of the extrapolation coefficient. A correction to the Taylor expansion involved in the RE formalism is proposed to take into account the singularity and to explain the majority of the RE behaviors observed