1,720,955 research outputs found
EXPERIMENTAL ANALYSIS OF TRANSITIONAL FLOWS UNDER TURBINE-LIKE CONDITIONS VIA APPLICATION AND DEVELOPMENT OF ADVANCED POST-PROCESSING TECHNIQUES
No full textThe present thesis is primarily devoted to developing and applying advanced post-processing techniques to inspect complex transitional boundary layer (BL) flows evolving under variable inflow conditions. A large amount of data has been experimentally acquired utilizing particle image velocimetry (PIV) and laser Doppler velocimetry (LDV) in a test section consisting of a flat plate installed between two adjustable endwalls. Depending on the Reynolds number (Re), the free-stream (FS) turbulence intensity (Tu) and the adverse pressure gradient (APG) imposed to the flow, attached or separated boundary layer transition was obtained.
The effects of the inflow parameters variation have been studied in detail, focusing on the flow statistical and dynamical behavior.
Due to the complexity and variety of the transitional phenomena, data-driven modal decomposition techniques have been employed to reduce the large amount of experimental data collected here. Moreover, new variants of well-established post-processing techniques have been developed to identify the main features embedded in the extensive databases.
In the case of separated flow transition, the modal decomposition procedures allowed a deep insight into the instability mechanism developing in the shear layer. Dynamic Mode Decomposition (DMD) was used to analyze the most unstable wavelengths related to the Kelvin-Helmholtz (K-H) vortices driving transition. Proper Orthogonal Decomposition (POD) was applied to PIV data, inspecting the main flow structures developing in the different regions of the LSB. Subsequently, an Extended Proper Orthogonal Decomposition (E-POD) procedure was applied, highlighting the correlation between the main dynamics observed in the forward part of the bubble and the breakup events occurring in the reattachment region.
Regarding the data reduction, the extensive database was used to develop new empirical correlations predicting the transition process regarding the geometry of a LSB and the related shedding process.
The transition process was systematically analyzed using decomposition techniques in the context of the free-stream turbulence induced transition. In order to inspect BL receptivity to free-stream disturbances, a variant of the E-POD was proposed, based on the correlating events between the FS and the BL. Low-order reconstructions of the original data were used to highlight the most correlating events directly linked to the formation and the breakup of streaky structures. Moreover, a turbulent spot recognition algorithm was implemented to identify the BL statistical response to the inflow parameters through the probability density function (PDF) of spot nucleation. Thus, a model for the PDF of spot nucleation is proposed as a function of the main flow parameters involved in the transition process.
Based on the results of the previous analyses, engineering correlations for predicting the free-stream turbulence induced transition are also introduced.
Independently on the transition type, results obtained employing the aforementioned procedures allowed a fruitful characterization of the different instability mechanisms developing in the first stage of transition, the description and evolution of coherent structures, and the correlation between their dynamics
Stability of low-pressure turbine boundary layers under variable Reynolds number and pressure gradient
No full textThe free-stream turbulence induced transition occurring under typical low-pressure turbine flow conditions is investigated by comparing linear stability theory with wind tunnel measurements acquired over a flat plate subjected to high turbulence intensity. The analysis was carried out, accounting for three different Reynolds numbers and four different adverse pressure gradients. First, a non-similarity-based boundary layer (BL) solver was used to compute base flows and validated against pressure taps and particle image velocimetry (PIV) measurements. Successively, the optimal disturbances and their spatial transient growth were calculated by coupling classical linear stability theory and a direct-adjoint optimization procedure on all flow conditions considered. Linear stability results were compared with experimental particle image velocimetry measurements on both wall-normal and wall-parallel planes. Finally, the sensitivity of the disturbance spatial transient growth to the spanwise wavenumber of perturbations, the receptivity position, and the location where disturbance energy is maximized were investigated via the built numerical model. Overall, the optimal perturbations computed by linear stability theory show good agreement with the streaky structures surveyed in experiments. Interestingly, the energy growth of disturbances was found to be maximum for all the flow conditions examined, when perturbations entered the boundary layer close to the position where minimum pressure occurs.</p
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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