1,721,035 research outputs found
LES modeling of scramjet combustion
No full textThe physics of supersonic combustion is analyzed in order to derive a new subgrid scale model for Large Eddy Simulation. Anisotropy associated to the directional Mach number typical of supersonic flows (i. e., M > 1 in only one direction) is explicitly considered by means of non-dimensionalized Navier-Stokes equations. The study shows that high Mach number flows experience mainly streamwise vorticity and consequently maximum helicity. Both affect mixing and may alter the turbulent kinetic energy decay by decreasing its rate, i.e., decreasing its characteristic spectral slope below that predicted by Kolmogorov scaling. Furthermore, it is analytically predicted that transversal pressure gradients increase vorticity, thus plausibly explaining the improved mixing realized by certain injectors. The supersonic regime is also found to affect the combustion regime: analysis of characteristic acoustic and convective times shows that while subsonic combustion takes place at approximately constant pressure, supersonic combustion takes place at approximately constant volume. Furthermore, collisional frequency is shown to increase due to local dilatation, resulting in faster kinetics and shorter ignition delay times. This effect could explain flame anchoring observed in some SCRJ combustor experiments. All the physical features and aspects of supersonic combustion found are used as ingredients to build a new subgrid scale model. In particular, micro-scale physics has been included by means of a subgrid kinetic energy equation that is algebraically modeled to provide the velocity fluctuation needed by the eddy viscosity SGS closure. Numerical simulations of a supersonic combustion NASA - Langley test case provide qualitative validation of the proposed model
Development of Thrust Chamber Components for a System Analysis Tool
No full textIn this paper a new thrust chamber component for the object oriented tool EcosimPro is presented. The numerical approach consists of a finite volume formulation of the unsteady quasi one-dimensional Euler equations for multispecies flow coupled with finite-rate chemistry. The inviscid convective fluxes are treated with two schemes, specifically formulated for multispecies flows: the approximate Riemann solver of Roe and the AUSM+ -up. Both the schemes are implemented with a spatial accuracy up to the third order by means of the Monotonic Upstream Centered Scheme for Conservation Laws (MUSCL). The reaction mechanism presented consists of six species and eight reactions for the combustion of hydrogen and oxygen while time integration is left to the DASSL implicit solver embedded in EcosimPro. After the description of the numerical model, some
validation test cases for the schemes and the finite-rate chemistry mechanism are presented. The component is then tested on the Space Shuttle Main Engine (SSME) Main Combustion Chamber (MCC) and the results are compared against those obtained with an already validated software. The tests show that the component is able to reach the expected steady-state solution in terms of both evolution of the thermodynamic properties and mixture composition and that the implicit solver is able to deal with the stiffness introduced by the source terms representing the finite-rate chemistry. The SSME MCC and its regenerative cooling channel are then modelled in EcosimPro. Limitations related with the use of classical semi-empirical correlations for the hot gas side heat transfer coefficient are highlighted and overcome through a coupling procedure, in which the solution coming from a CFD analysis of the MCC is coupled with those obtained with EcosimPro for the cooling channels. The results of this iterative procedure are compared with those available in open literature, showing that wall heat flux and wall temperature profile are in line with those obtained by other methods. Furthermore, an accurate calculation of the wall heat flux allows the cooling channel component presently available in EcosimPro to obtain results that are comparable with those proposed by higher fidelity models
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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