1,720,989 research outputs found
Discontinuous Galerkin solution of the Reynolds averaged Navier Stokes and k-omega turbulence model equations
No full textDiscontinuous Galerkin methods, originally developed in the advective case, have been successively extended to advection–diffusion problems, and are now used in very diverse applications. We here consider
the numerical solution of the compressible Reynolds-averaged Navier–Stokes and k–w turbulence model equations by means of DG space discretization and implicit time integration. Detailed description of the
DG discretization of the viscous part of the equations and of several implementation details of the k–w turbulence model are given. To assess the performance of the proposed methodology we present the results
obtained in the computation of the turbulent flow over a flat plate and of the turbulent unsteady wake developing behind a turbine blade
Simulation of the Transitional Flow in a Low Pressure Gas Turbine Cascade With a High-Order Discontinuous Galerkin Method
No full textIn the last decade, discontinuous Galerkin (DG) methods have been the subject of extensive research efforts because of their excellent performance in the high-order accurate discretization of advection-diffusion problems on general unstructured grids, and are nowadays finding use in several different applications. In this paper, the potential offered by a high-order accurate DG space discretization method with implicit time integration for the solution of the Reynolds-averaged Navier-Stokes equations coupled with the k-ω turbulence model is investigated in the numerical simulation of the turbulent flow through the well-known T106A turbine cascade. The numerical results demonstrate that, by exploiting high order accurate DG schemes, it is possible to compute accurate simulations of this flow on very coarse grids, with both the high-Reynolds and low-Reynolds number versions of the k-ω turbulence model
Modified extended BDF scheme for the discontinuous Galerkin solution of unsteady compressible flows
No full textIn this paper, a high-order DG method coupled with a modified extended backward differentiation formulae (MEBDF) time integration scheme is proposed for the solution of unsteady compressible flows. The objective is to assess the performance and the potential of the temporal scheme and to investigate its advantages with respect to the second-order BDF. Furthermore, a strategy to adapt the time step and the order of the temporal scheme based on the local truncation error is considered. The proposed DG-MEBDF method has been evaluated for three unsteady test cases: (i) the convection of an inviscid isentropic vortex; (ii) the laminar flow around a cylinder; and (iii) the subsonic turbulent flow through a turbine cascade
Robustness and efficiency of an implicit time-adaptive discontinuous Galerkin solver for unsteady flows
No full textHigh-fidelity fluid dynamics simulations of unsteady flows are nowadays of great interest for many industrial fields. This class of simulations, as they are characterized by a wide range of temporal scales, requires robust, accurate and efficient long time integration strategies. These features can be achieved by an appropriate coupling of high-order time integration schemes and time-step adaptation algorithms. The adaptation algorithms are typically based on a local error estimator, which exploits the local truncation error of the time integration scheme and of its lower order embedded scheme. In literature few information are available to assess the benefits in terms of robustness, accuracy, and efficiency provided by the coupling between temporal schemes and adaptation strategies for unsteady CFD simulations. The aim of this work is to reduce this gap, presenting a numerical investigation of the performance for different adaptive time-step strategies, based on implicit Rosenbrock-type temporal schemes, in a high-order discontinuous Galerkin solver. The performance of the considered time integration strategies for the autonomous ODE system resulting from the DG space discretization of the Navier–Stokes equations is assessed for several test cases of increasing stiffness and difficulty, identifying the best scheme and algorithm: (i) the 2D laminar flow around a circular cylinder and around a tandem of cylinders at ReD=100; (ii) the 2D viscous flow through a porous media, modelled as an array of cylinders, at ReD=2100 and ReD=10,000; (iii) the 3D turbulent flow through a 4-wheels rudimentary landing gear (RLG) at ReD=1×106
p -Multigrid High-Order Discontinuous Galerkin Solution of Compressible Flows
No full textDiscontinuous finite element methods are finding widespread use in a wide range of scientific and technical applications since they are among the few available methods for the approximation of partial differential problems that combines high-order accuracy, geometric flexibility, and robustness. The price to pay for the robustness, accuracy, and flexibility of these methods is their high computational cost and storage requirement. However, the computational efficiency of discontinuous finite element methods can be substantially improved by resorting to multilevel solution techniques. This chapter presents the application of a p-multigrid high-order accurate discontinuous finite element method to the numerical solution of compressible laminar viscous flows (compressible Navier–Stokes equations) and to compressible turbulent flows modeled with the Reynolds-Averaged Navier–Stokes equations coupled with the k- ω turbulence model
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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