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Dynamics of large droplets in turbulent channel flow
Get PDFIn this work the behaviour of large deformable droplets dispersed in a wall bounded turbulent flow has been investigated focusing on the role of the droplets deformability.
A simplified physical problem has been considered: density differences and viscosity differences between the two fluids have been neglected while surface tension effects and coalescence/breakup events have been considered. A wide range of Weber numbers We (ratio between inertial forces and surface tension) have been investigated at moderate friction Reynolds numbers Re_\tau = 100 \div 150.
Under these assumptions the problem represents an archetypal model of an industrial turbulent multiphase flow in which only hydrodynamics and capillary effects are considered.
The problem has been studied applying a hierarchical decomposition: first the momentum transfer at the interface of a single large deformable non-breaking droplet in turbulence has been investigated, then the analysis has been extended to a swarm of large droplets: effects on the turbulent wall-drag and the coalescence rate have been measured.
The results show flow field modifications in the vicinity of the droplet interface: the flow field deflections at the interface are smaller the larger is the interface deformability. As a consequence also an increment of the local shear stress is observed when decreasing the droplet deformability (namely, decreasing We).
The role of deformability is central in the wall drag modifications produced by a large number of droplets; droplets with large Weber number can transport more efficiently small velocities from the near wall regions towards the high velocity regions of the channel center and vice-versa.
The deformability is also a leading parameter in determining the coalescence rate and the possibility of breakup of the droplets swarm: when We1 (inertial larger than surface tension).
As a conclusion, large droplets in wall bounded turbulence can produce modifications of the flow field depending on their deformability. Significant Drag Enhancement (DE) is registered when the Weber number is smaller than a critical value (We1, while We_c<1. This indicates that the wall drag modifications are weakly dependent on the droplet diameters d when their size is comparable to the channel heigh
Turbulence modification by dispersion of large deformable droplets
No full textDispersion of large deformable droplets in turbulent channel flow is investigated: the fluids are considered Of same density and viscosity for a broad range of plausible values of surface tension. Droplets much larger than the Kolmogorov length scale are released in a channel flow; the turbulent flow is computed with pseudo-spectral Direct Numerical Simulations (DNS), while phase interactions are described with a Phase Field Model (PFM). It is shown that droplets segregation toward the center of the channel is promoted by deformability in particular, for the considered Weber numbers (ratio between inertia and surface tension), droplets do not deposit on the walls. The turbulent flow is modified by the presence of the droplets: for small values of We the wall drag is increased with respect to the single phase flow. The wall drag enhancement reduces increasing We and its time evolution depends on the droplets coalescence and breakup rates
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
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