1,720,965 research outputs found
Aerodynamics and aeroacoustics survey for a low speed subsonic jet operating at mach 0.25
Get PDFThe purpose of this work is to study and characterize, in laboratory, the aerodynamics of a free jet operating at subsonic regime and identify its acoustic signature. This study aims to analyze the fundamental role of turbulent flow structures in the total noise produced at different Mach numbers. This work is focused at low speed subsonic jets operating at Mach number 0.25. The research is done by analyzing the data obtained in experiments using Pitot tube, hot-wire anemometer and acoustic measurements. This work also describes the experimental procedures for each step of analysis, as well as the characteristics of jet noise facility. The data from measurements with Pitot tube is used to study the mean velocity profiles. The average properties are also analyzed with anemometry system, likewise used to study the turbulent intensity of eleven axial lines, ranging from the center line to the edge of the nozzle (lipline). These results are compared with the literature and is verified the accuracy of hot-wire anemometers for turbulent intensities lower than 15%. A database with the sound pressure level as a function of frequency is constructed from experiments serving as data for further numerical analysis to solve this problem
A survey of the turbulence statistics of a model-scale installed jet at low and moderate mach numbers
No full textIn modern high-bypass ratio engine configurations, the exhausted jet is deflected and modified by the wing and high lift devices. The present paper reports a survey on a model-scale jet in the presence of a flat plate installed at two height (h) and two length (l) positions from the center of the nozzle. The aim of this work is to evaluate the one-point statistics of isolated and installed jets. Experimental data of the axial component of the velocity is acquired for a 1½” nozzle via hot-wire anemometry. The investigation is made for several jet velocities, ranging from acoustical Mach numbers 0.2 to 0.8. Mean velocity profile results show a slight acceleration of the jet in regions close to the plate. This effect is notorious for plate locations in which the jet wets the plate close to the nozzle exit. It also seems to have a weak velocity dependency. This acceleration of the jet is consistent with the conservation of mass and changes in the entrainment at that region. As a direct result of the local jet acceleration, locations close to the plate present lower levels of turbulence intensity. Other factor that may contribute to this effect is the break-down of the eddies at the rigid surface. Turbulence intensity profiles have also shown a spike immediately downstream of the trailing edge. This is possibly an effect of the boundary layer separation, or a wake-type of flow originated at the trailing edge. Results for low and higher-order statistics of the shear layer opposite to the plate are exactly the same as results measured for the isolated jet configuration. Boundary layer development along the plate in both streamwise and spanwise direction is presented. It is shown that, even though the present problem consists of a non-uniform flow interacting with a surface, boundary layer properties could be defined for close-coupled, long surfaces. Finally, the spectra information from hot-wire sensors are analysed and qualitatively compared to the spectra measured by near-field surface pressure transducers located streamwise along the plate. The power spectral density of the velocity signal has a -5/3 decay, which is not seen in the pressure spectra.</p
Wall pressure fluctuations induced by a single stream jet over a semi-finite plate
No full textThis work provides an experimental investigation into the interaction between a jet flow and a semi-finite plate parallel to the jet. Wall pressure fluctuations have been measured in a high compressible subsonic regime and for different distances between the jet and the plate trailing edge. The experiment has been carried out in the ISVR anechoic Doak Laboratory at the University of Southampton, using wall pressure transducers flush mounted on the plate surface. Signals were acquired in the stream-wise direction along the jet centreline and in the span-wise direction in a region close to the trailing edge. The radial position of the flat plate was fixed very close to the jet axis to simulate a realistic jet–wing configuration. The plate was moved axially in order to investigate four different jet-trailing edge distances and to include measurements upstream of the nozzle exhaust. The acquired database was analyzed in both the frequency and the time domains providing an extensive statistical characterization in terms of spectral uni– and multi–variate quantities as well as high order statistical moments. A wavelet analysis was performed as well to investigate the time evolution of the wall pressure events
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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