1,721,056 research outputs found
Flow and Viscous Effects on Impedance Eduction
No full textIn principle, the impedance of a locally reacting acoustic liner should be independent of the structure of the sound
field above the liner. Some experimental studies, however, have found that the impedance inversely determined by
available eduction techniques is actually dependent on the direction of incident waves relative to the mean flow. This
dependence has mainly been attributed to the incomplete description of flow physics in the eduction techniques,
particularly to the neglect of the viscous effects. The purpose of the paper is to examine whether such a wave-direction
dependence can be removed by including the flow physics that is absent in previous eduction techniques. To this end,
two eduction methods using the full linearized Navier–Stokes equations are proposed. Possible turbulent effects are
considered by using available turbulence models. The proposed eduction methods are applied to new measurement
data and data available in the literature, and are compared with another eduction method that has been commonly
used in the community. The results show that including viscous effects does not resolve the controversy on the
apparent wave-direction dependence
Experimental Assessment of Noise Generation and Transmission in a High-Pressure Transonic Turbine Stage
No full textThe noise originating from the core of an aero-engine is usually difficult to quantify and the knowledge about its Generation and propagation is less advanced than that for other engine components.
In order to overcome the difficulties associated with dynamic measurements in the crowded core region, dedicated experiments have been set up in order to investigate the processes associated with the generation of noise in the combustor, its propagation through the turbine and the interaction of these two components,
which may produce additional - so-called indirect combustion-noise. In the current work, a transonic turbine stage installed at the Laboratorio di Fluidodinamica delle Macchine of the Politechnico di Milano was exposed to acoustic, entropic, and vortical disturbances. The incoming and outgoing sound fields were analyzed in detail by two large arrays of microphones.
The mean flow field and the disturbances were carefully mapped by several aerodynamic and thermal probes. The results include transmission and reflection characteristics of the turbine stage, latter one was found to be much lower than usually assumed.
The modal decomposition of the acoustic field in the upstream and downstream section show beside the expected rotor-stator interaction modes additional modes. At the frequency of entropy or respectively vorticity excitation, a significant increase of the overall sound power level was observed
Indirect Noise Generation in a High Pressure Turbine Stage
No full textIn order to enhance the insight into core noise generation mechanisms in aero-engines this work investigates the noise generation by accelerated entropy and vorticity fluctuations in a high pressure turbine stage. The experiments are conducted in the high pressure turbine facility at Politecnico di Milano in the framework of the European funded project RECORD (Research on Core Noise Reduction). The entropy and vorticity perturbations are produced by a custom-built injection system. The sound fields up-and downstream of the turbine stage are analyzed by the application of two microphone arrays with more than 200 microphones in total. The results indicate that on the upstream section of the turbine stage the generated noise is potentially dominated by the vorticity noise or the direct noise from the injection system. On the downstream side of the turbine stage a clear linear dependence of the generated entropy sound power from the squared values of the injected temperature fluctuation amplitudes is detected for the different operation conditions. This confirms the basic theoretical understanding of entropy noise generation and gives the opportunity for exploiting this knowledge to full-scale application on aero-engines
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
- …
