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Computational methodology for investigating the transient interaction between a reaction control jet and a hypersonic crossflow
No full textA computational methodology has been developed to investigate the transient start of a Reaction Control (RC) jet into a hypersonic cross flow. The method uses the rhoCentral-Foam solver, which forms part of the OpenFOAM Computational Fluid Dynamics (CFD) package. Results have been compared to analytical solutions and previous simulations of a one-dimensional shock tube, a two-dimensional wedge, a diamond airfoil and a forward step. Further evidence of validation has been gained by comparing results with experimental data for a two-dimensional jet issuing into a quiescent atmosphere, and the steady interaction between a three-dimensional RC jet and a hypersonic cross flow. This work extends the scope of validation data available for rhoCentralFoam in open literature. Results show that the rhoCentralFoam solver performs well, and is able to capture all relevant flow structures. Shock properties, velocity and density fields were well predicted, but accuracy was decreased in some cases when predicting temperature and pressure fields. Overall, the numerical scheme is suitable for investigating the transient interaction between an RC jet and a hypersonic cross flow
Numerical investigation of a pulsed reaction control jet in hypersonic crossflow
Get PDFThis paper presents a numerical study on the flow structures developed when a pulsed reaction control jet is operated in a hypersonic crossflow with a laminar boundary layer. Understanding these flow structures is important to the design of reaction control jets and scramjet fuel injectors. Implicit large-eddy simulations were performed with a round, sonic, perfect air jet issuing normal to a Mach 5 crossflow over a flat plate, at a jet-to-crossflow momentum ratio of 5.3 and a pressure ratio of 251, and with square-wave pulsing at Strouhal numbers of 1/6 to 1/3, based on jet diameter and free-stream velocity. Pulsing the jet allows the shock structure to partially collapse when the jet is off. This shock collapse affects the shedding frequency of shear-layer vortices, the formation of shear-layers downstream of the jet outlet, and the formation of longitudinal counter-rotating vortices. The lead shocks formed at jet start-up allow deeper penetration by increasing the effective jet-to-crossflow momentum ratio near the jet outlet and by preventing interaction between hairpin vortices. Normalised penetration was increased by a maximum of 68% compared with the steady jet. Pulsing also provides a higher jet interaction force per unit mass flow rate compared with a steady jet, with a 52% increase recorded at a 33% duty cycle. Temporal and spatial variations of surface pressure are important for reaction control applications and have been quantified. Pressure distribution depends strongly on duty cycle, and higher interaction force per unit mass flow rate was observed in cases with low duty cycle.</p
Transient interaction between a reaction control jet and a hypersonic crossflow
Get PDFThis paper presents a numerical study that focuses on the transient interaction between a reaction control jet and a hypersonic crossflow with a laminar boundary layer. The aim is to better understand the underlying physical mechanisms affecting the resulting surface pressure and control force. Implicit large-eddy simulations were performed with a round, sonic, perfect air jet issuing normal to a Mach 5 crossflow over a flat plate with a laminar boundary layer, at a jet-to-crossflow momentum ratio of 5.3 and a pressure ratio of 251. The pressure distribution induced on the flat plate is unsteady and is influenced by vortex structures that form around the jet. A horseshoe vortex structure forms upstream and consists of six vortices: two quasi-steady vortices and two co-rotating vortex pairs that periodically coalesce. Shear-layer vortices shed periodically and cause localised high pressure regions that convect downstream with constant velocity. A longitudinal counter-rotating vortex pair is present downstream of the jet and is formed from a series of trailing vortices which rotate about a common axis. Shear-layer vortex shedding causes periodic deformation of barrel and bow shocks. This changes the location of boundary layer separation which also affects the normal force on the plate.</p
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
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
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