An algebraic subgrid scale finite element method for the convected Helmholtz equation in two dimensions with applications in aeroacoustics

An algebraic subgrid scale finite element method formally equivalent to the Galerkin Least-Squares method is presented to improve the accuracy of the Galerkin finite element solution to the two-dimensional convected Helmholtz equation. A stabilizing term has been added to the discrete weak formulation containing a stabilization parameter whose value turns to be the key for the good performance of the method. An appropriate value for this parameter has been obtained by means of a dispersion analysis. As an application, we have considered the case of aerodynamic sound radiated by incompressible flow past a two-dimensional cylinder. Following Lighthill’s acoustic analogy, we have used the time Fourier transform of the double divergence of the Reynolds stress tensor as a source term for the Helmholtz and convected Helmholtz equations and showed the benefits of using the subgrid scale stabilization

A heuristic argument for the sole use of numerical stabilization with no physical LES modeling in the simulation of incompressible turbulent flows

We aim at giving support to the idea that no physical Large Eddy Simulation (LES) model should be used in the simulation of turbulent flows. It is heuristically shown that the rate of transfer of subgrid kinetic energy provided by the stabilization terms of the Orthogonal Subgrid Scale (OSS) finite element method is already proportional to the molecular physical dissipation rate (for an appropriate choice of the stabilization parameter). This precludes the necessity of including an extra LES physical model to achieve this behavior and somehow justifies the purely numerical approach to solve turbulent flows. The argumentation is valid for a fine enough mesh with characteristic element size, $h$, so that $h$ lies in the inertial subrange of a turbulent flow

Computational aeroacoustics of viscous low speed flows using subgrid scale finite element methods

A methodology to perform computational aeroacoustics (CAA) of viscous low speed flows in the framework of stabilized finite element methods is presented. A hybrid CAA procedure is followed that makes use of Lighthill's acoustic analogy in the frequency domain. The procedure has been conceptually divided into three steps. In the first one, the incompressible Navier–Stokes equations are solved to obtain the flow velocity field. In the second step, Lighthill's acoustic source term is computed from this velocity field and then Fourier transformed to the frequency domain. Finally, the acoustic pressure field is obtained by solving the corresponding inhomogeneous Helmholtz equation. All equations in the formulation are solved using subgrid scale stabilized finite element methods. The main ideas of the subgrid scale numerical strategy are outlined and its benefits when compared to the Galerkin approach are described. As numerical examples, the aerodynamic noise generated by flow past a two-dimensional cylinder and by flow past two cylinders in parallel arrangement are addressed

Inestabilitats numèriques i turbulència : l'efecte de les subescales en mecànica de fluids

En aquest treball descrivim dos enfocaments per a l'estudi de les equacions de Navier-Stokes que tradicionalment s'han analitzat de manera independent però per als quals hi ha un nexe d'unió: la descripció matemàtica de la turbulència en problemes de mecànica de fluids i les inestabilitats numèriques que s'observen quan les equacions que regeixen el fenomen s'aproximen amb algun mètode numèric. En ambdós casos, l'objectiu és plantejar un problema aproximat no per a la velocitat i pressió del problema continu, sinó per a una certa component «capturable» en sentit numèric d'aquestes incògnites.In this work we describe two approaches to study the Navier-Stokes equations that, traditionally, have been analyzed independently, but for which there is a natural link: the mathematical description of turbulence in fluid mechanics and the numerical unstabilities encountered when the equations that describe the problem are approximated numerically. In both cases, the objective is to set a problem not for the velocity and pressure of the continuous problem, but for a certain component of these unknowns that can be «captured» in a numerical sense

Parler en L1 pour ecrire en L2

Un des aspects qui caractérise les procédures d’écriture en L2 par rapport à celles mises en œuvre en L1 est le recours à la L1 pour faciliter la rédaction. En situation d’écriture collective dans des contextes de contact de langues, l’usage de cette L1 dans l’interaction prend des formes spécifiques. Dans cet article nous analysons les conditions d’emploi de la L1 et sa double dépendance par rapport aux différents types d’activités interactionnelles et aux normes d’usage.One of the characteristics which differenciates writing processes in L2 as opposed to L1 is the possibility of using L1 as a strategy to facilitate composition. The presence of this L1 in the L2 composition process has some special features in group writing situations in contexts where the languages are in everyday contact. In this article, we analyse the way in which L1 use is determined : by norms of use, and by the (group) writing process itself

La enseñanza de las lenguas en la educación primaria

Los diseños curriculares de las áreas de lengua definidos en el marco de la reforma de la enseñanza obligatoria se han hecho eco en líneas generales de las nuevas directrices surgidas de las aportaciones de la lingüística, la psicología y la pedagogía, y fundamentan sus propuestas en una concepción funcional del lenguaje, una concepción constructivista del aprendizaje y una concepción activa y comunicativa de la enseñanza de la lengua. Pero la propuesta de renovación de la enseñanza de la lengua no se ha producido solamente en el ámbito teórico y metodológico. Por una parte, desde la Constitución de 1978, nuestro país se reconoce como un país plurilingüe en el que conviven diversas lenguas; por otra, la integración plena de España en la Comunidad Europea ha hecho más evidente la necesidad de tener en cuenta la diversidad lingüística de nuestro continente

Processos de composició escrita i programes d'immersió : els canvis de llengua en la interacció per a la composició en L2 /

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