1,720,991 research outputs found
Dispersed bubble and particle-laden turbulent flows in the two-way coupling regime
Full text linkThe momentum exchange of bubble and particle laden incompressible turbulent flows is investigated by means of Direct Numerical Simulations (DNS), employing the Eulerian-Lagrangian approach. The Exact Regularised Point Particle method (ERRP) is used to achieve the inter-phase momentum coupling between the two phases.
The first part of the research deals with bubble-laden turbulent homogeneous shear flow. The aim of this study consists in addressing the modulation of shear turbulence and the bubble clustering geometry in presence of different inter-phase momentum coupling conditions. Suspensions with different combinations of void fraction and Kolmogorov-based Stokes number, in the dilute regime, are studied. Bubbles suppress the turbulent kinetic energy and turbulent dissipation as well. Turbulent modulation occurs via the direct change of the Reynolds shear stress. In fact, the bubble energy source is proved to be negligible in the scale-by-scale turbulent energy budget. The bubble clustering, in agreement with the literature, occurs in the form of thin elongated structures. The clusters are aligned with principal strain direction of the mean flow, as usual in shear flows. The bubble clustering and turbulent modification are strictly related: both increase with the Stokes number and are independent of the void fraction, in the range of parameters considered in our simulations. The data show that the turbulent modification is disadvantaged when the bubble distribution is homogeneous (i.e. small Stokes number). Finally, the small scale bubble clustering is slightly reduced by two-way coupling effects
even though the clustering anisotropy still persists at small scales as it occurs for inertial particles. In the next stage of the research, the objective is to study multiphase wall-bounded turbulent flows. Under the same flow rate, the dispersed phase can either reduce, as in bubbly-flows, or increase, as in particles-laden flows, the viscous wall drag. However, it is well acknowledged that bubbles must be large, and deformable, in order to reduce the viscous resistance in wall turbulence. On the other hand it is known that small inertial particles lead to a wall drag increase.
Since we are interested on important turbulence modifications, the second part of the research is devoted to particle-laden wall turbulence flows. In this new investigation, the turbulence modulation is addressed in an particle-laden annular pipe flow, via Direct Numerical Simulation (DNS). The alteration of the heat exchange induced by the different turbulent mixing is studied as well. The turbulence modulation induced by small particles is addressed for the first time in the annular geometry, in the context of Direct Numerical Simulations. A wall correction is included in ERPP in order to take into account wall effects in the particle disturbance. The research also focuses on the particle preferential concentration close to the wall, the so-called turbophoresis.
The relation between the particle concentration and the friction wall drag and heat exchange modification is explored. The first and second moment statistics, the two-point correlation functions and the energy spectra are studied. The two-way coupled momentum exchange leads up to 30% wall drag increase. The phenomenon is controlled by the particle mass loading and the wall radius ratio Ri/Ro, where Ri is the internal wall radius and Ro the external one. The mechanism leading to the increase of resistance is attributed to the modified Reynolds shear stress.
The heaviest suspensions show a drastic modification of the coherent structures by the external wall, although the flow is altered in the whole annular pipe. The TKE significantly increases close the external wall, while it is suppressed close the internal wall. The increase of the heat-exchange, induced by the different turbulent mixing, is small, below 5%. In the annular pipe the dispersed phase preferentially migrates toward the external wall. In fact, the internal peak of the particle concentration is up to 100 times lower than the external one. Moreover, the findings suggest that the particle concentration is largely overestimated in the central and internal regions, in the one-way coupling regime ( i.e. no turbulence modification ).
In fact, the particle feedback promotes the turbophoresis of the external wall, while the particle accumulation close the internal side is attenuated
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
Corner liquid imbibition during capillary penetration in lithographically made microchannels
No full textDispelling 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
Reaction spreading on graphs
No full textWe study reaction-diffusion processes on graphs through an extension of the standard reaction-diffusion equation starting from first principles. We focus on reaction spreading, i.e., on the time evolution of the reaction productM(t). At variance with pure diffusive processes, characterized by the spectral dimension d(s), the important quantity for reaction spreading is found to be the connectivity dimension d(l). Numerical data, in agreement with analytical estimates based on the features of n independent random walkers on the graph, show that M(t) t(dt). In the case of Erdos-Renyi random graphs, the reaction product is characterized by an exponential growth M(t) similar to e(alpha t) with alpha proportional to ln , where is the average degree of the graph
Probability distribution of intrinsic filtering errors in Lagrangian particle tracking in LES flow fields
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