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High-order discontinuous Galerkin solutions of three-dimensional incompressible RANS equations
Full text linkAssessment of a high-order discontinuous Galerkin method for incompressible three-dimensional Navier–Stokes equations: Benchmark results for the flow past a sphere up to Re=500
No full textThis paper deals with the implementation of the high-order Discontinuous Galerkin (DG) artificial compressibility flux method into a three-dimensional incompressible Navier–Stokes (INS) solver. The method is fully implicit in time and its distinguishing feature is the formulation of the inviscid interface flux, which is based on the solution of the Riemann problem associated with a local artificial compressibility-like perturbation of the equations.
The code has been tested on a wide range of flow regimes considering the flow past a sphere at moderate Reynolds numbers. In order to asses the code reliability and its accuracy in space, up to the sixth order polynomial approximation, and in time, up to the fourth order, both steady (Re = 20, 200, 250) and unsteady (Re = 300, 500) problems have been approached.
With the largest Reynolds number here considered the flow exhibits a complex behavior, even if it still laminar, since undergoes the transition from a regular to an almost chaotic system. For this problem, for which the flow field characteristics are not completely well established and no many data are available in the present literature, detailed results are reported in this paper
A Spalart-Allmaras turbulence model implementation in a discontinuous Galerkin solver for incompressible flows
Full text linkIn this paper the artificial compressibility flux Discontinuous Galerkin (DG) method for the solution of the incompressible Navier–Stokes equations has been extended to deal with the Reynolds-Averaged Navier–Stokes (RANS) equations coupled with the Spalart–Allmaras (SA) turbulence model. DG implementations of the RANS and SA equations for compressible flows have already been reported in the literature, including the description of limiting or stabilization techniques adopted in order to prevent the turbulent viscosity View the MathML sourceν˜ from becoming negative. In this paper we introduce an SA model implementation that deals with negative View the MathML sourceν˜ values by modifying the source and diffusion terms in the SA model equation only when the working variable or one of the model closure functions become negative. This results in an efficient high-order implementation where either stabilization terms or even additional equations are avoided. We remark that the proposed implementation is not DG specific and it is well suited for any numerical discretization of the RANS-SA governing equations. The reliability, robustness and accuracy of the proposed implementation have been assessed by computing several high Reynolds number turbulent test cases: the flow over a flat plate (Re=107Re=107), the flow past a backward-facing step (Re=37400Re=37400) and the flow around a NACA 0012 airfoil at different angles of attack (View the MathML sourceα=0°,10°,15°) and Reynolds numbers (Re=2.88×106,6×106Re=2.88×106,6×106)
High-order discontinuous Galerkin RANS solutions of the incompressible flow over a delta wing
Full text linkIn this paper, high-order Discontinuous Galerkin (DG) Reynolds Averaged Navier Stokes (RANS) computations of the turbulent incompressible flow over a 65° deg sweep delta wing are presented. The flow regimes and the wing geometric configuration refer to those adopted in the international Vortex Flow Experiment 2 (VFE-2) project (Hummel, 2009). Here we consider the incompressible case, at Reynolds numbers 10^6 and 2 × 10^6, which has not yet been analyzed in-depth in literature from the numerical point of view. An extensive comparison of our results with experimental data, mainly those obtained by Furman and Breitsamter (2006, 2008, 2009, 2013) is here supplied.
As regards the turbulence modeling approach, recent researches have revealed that fully-turbulent RANS computations, at Reynolds number greater than 3 × 10^6 and at Mach numbers above 0.4, predict the main flow field features correctly.
The same behavior was not observed in the incompressible case, however we have found that it is sufficient to fix a turbulent transition, at approximately the 25% of the delta wing root chord, to greatly improve the results quality.
The employed transition model is quite simplistic and the resulting simulation approach is not in general completely satisfactory, however the results accuracy establishes the major role of the turbulent transition in predicting the delta wing flow-field. Moreover our solutions fully confirm the interpretation of this flow given by Furman and Breitsamter (2006, 2008, 2009, 2013). Finally, these computations put in evidence the robustness and the effectiveness of our high-order DG solver in dealing with large and complex problems on massively parallel architectures, using up to 4096 CPU cores
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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