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Discontinuous Galerkin Method for the numerical investigation of the effects of an active Gurney flap on the characteristics of an airfoil
No full textIn the last two decades in fluid dynamics it has been reported an increasing attention toward higher order methods because of their capability to simulate with great accuracy some phenomena involving wave propagation and/or turbulence which are of great practical interest. At the same time the methods based on a Discontinuous Galerkin formulation for the spatial discretization have been investigated with increasing interest since the correspondent high order versions of the methods traditionally employed in fluid dynamics (Finite Elements Methods, Finite Volumes and Finite Differences) have shown important drawbacks in terms of efficiency or their implementation is hard. Nowadays the Discontinuous Galerkin Method can be considered mature as a great amount of numerical studies are available in literature in which the properties of this discretization such as robustness and stability are investigated. However studies regarding complex applications of practical interest are still missing. In this work an efficient Discontinuous Galerkin method is proposed for the solution of the Favre averaged Navier Stokes equations written adopting an Arbitrary Lagrangian Eulerian formulation, for turbulent compressible flows in two dimensions and for bodies whose velocity with respect to the mean flow field is not constant. The turbulence model is based either on the Spalart Allmaras equation or the k-ω. To partially mitigate its intrinsic high computational cost, a nodal formulation of the Discontinuous Galerkin Method was adopted. The integration in time of the governing equations is carried out either with an explicit Runge-Kutta fourth order scheme or with an implicit time discretization based on a preconditioned Generalized Minimal RESidual algorithm for the solution of the Newton linearized system. The numerical model is applied to the solution of unsteady flows associated to an actively controlled Gurney Flap (or micro-tab) located in proximity of the trailing edge of an airfoil, with oscillations up to 20Hz. Several configurations of deployment motions are considered under different free stream conditions in order to demonstrate the capability of the solver to predict accurately unsteady non-linear problems at high Reynolds numbers. Moreover the numerical calculations are compared with experimental data in the case of the NACA 0012 airfoil, and of a modified version of the base shape employed in the experiments whose trailing edge is slightly thickened in order to accommodate the Gurney flap and the mechanism for the active flap tests. The results are in good agreement with the experimental data. The flow scenarios proposed in literature in the case of a static Gurney flap, under different flow conditions and flap geometries, are confirmed. The dynamic case is investigated for different motion frequencies and flap heights, and compared with available experimental data. Extensive numerical simulations of active Gurney flaps are still missing, and the present work represents an attempt to give an insight into the effectiveness of active flaps
Discontinuous Galerkin Method for the Study of Active Gurney Flaps
No full textA discontinuous Galerkin method is proposed for the solution of the Reynolds-averaged Navier-Stokes equations, for turbulent flows in two dimensions. The numerical model is applied to the solution of unsteady flows associated to an actively controlled Gurney flap located in proximity of the trailing edge of an airfoil, with oscillations up to 20 Hz. The motion of the Gurney flap is simulated through no-slip viscous wall conditions applied to the interfaces between neighboring elements that coincide with the position of the flap at a given time instant. Several configurations of deployment motions are considered under different freestream conditions to demonstrate the capability of the solver to predict accurately unsteady nonlinear problems at high Reynolds numbers. The numerical calculations are compared with experimental data in the case of the NACA 0012 airfoil
A Discontinuous Galerkin Method for the Solution of the Linearized Navier-tokes Equations
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Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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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