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iTi Conference on Turbulence III
No full textThe objectives of this conference are comprising basic research as well as research related to application. Therefore, both engineers and physicists working in the field of turbulence joined the conference. The invited speakers presented their contributions in fields of experimental, numerical, and theoretical research. Discussed topics are - Fundamentals, Modeling, Simulation (DNS and LES), Mathematical Methods, Coherent structure/Vortices, Scaling Laws and Intermittency, - Experiments, Large Re flows experiments, Convection, Polymer and Scalar, Scalar Mixing and Particle, Turbulent Boundary Layers, Atmospheric flows, MHD. A special session on turbulence effects on the wind energy conversion process has been organized
Progress in Turbulence V: Proceedings of the ITi Conference in Turbulence 2012
No full textThis volume collects the edited and reviewed contributions presented in the 5th iTi Conference in Bertinoro. covering fundamental aspects in turbulent flows. In the spirit of the iTi initiative, the volume is produced after the conference so that the authors had the possibility to incorporate comments and discussions raised during the meeting.
Turbulence presents a large number of aspects and problems, which are still unsolved and which challenge research communities in engineering and physical sciences both in basic and applied research. The book presents recent advances in theory related to new statistical approaches, effect of non-linearities and presence of symmetries. This edition presents new contributions related to the physics and control of laminar-turbulent transition in wall-bounded flows, which may have a significant impact on drag reduction applications. Turbulent boundary layers, at increasing Reynolds number, are the main subject of both computational and experimental long research programs aimed at improving our knowledge on scaling, energy distribution at different scales, structure eduction, roughness effects to name only a few. Like previous editions several numerical and experimental analysis of complex flows, mostly related to applications, are presented.
The structure of the present book is as such that contributions have been bundled according to covering topics i.e. I Theory, II Stability, III Wall bounded flows, IV, Complex flows, V Acoustic, VI Numerical methods.
The volume is dedicated to the memory of Prof. Rudolf Friedrich who prematurely died in Münster/Germany on the 16th of August 2012. In his honor the conference has started with a special session dedicated to his work
iTi Conference on Turbulence IV
No full textDal 19 al 24 settembre il CeUB di Bertinoro ha ospitato la quarta edizione dell’iTi Conference on Turbulence, cioè del Convegno interdisciplinare sulle tecnologie applicate allo studio della turbolenza, coordinato dal Prof. Martin Oberlack della Technische Universität di Darmstadt, dal Prof. Jochim Peinke della Carl von Ossietzky Universität di Oldenburg e dal Prof. Alessandro Talamelli della Seconda Facoltà di Ingegneria dell’Università di Bologna con sede a Forlì. Il convegno ha affrontato aspetti innovativi sia per quanto riguarda la ricerca di base che quella applicata e si è rivolto, quindi, sia agli ingegneri che ai fisici che si occupano della turbolenza sviluppandone in particolare le diverse problematiche nei campi della ricerca sperimentale, numerica o teorica.
Al centro del dibattito, a cui hanno partecipato tra i più famosi ricercatori del settore provenienti da tutte le parti del mondo, sono stati trattati temi come la simulazione e modellizzazione, nuove metodologie matematiche, vortici e strutture coerenti, leggi di scala, la convezione turbolenta, gli strati limite atmosferici e la turbolenza magneto-idrodinamica.
Durante il convegno è stata organizzata una visita al laboratorio internazionale per gli studi sulla turbolenza CICLoPE (Center for International Cooperation in Long Pipe Experiments) in fase di realizzazione presso i tunnel delle “Ex Industrie Caproni” a Predappio, finanziato dall’Università di Bologna in collaborazione con Regione Emilia Romagna, Provincia di Forlì-Cesena e Comune di Predappio.
Ha chiuso il convegno un workshop dal titolo The Impact of Turbulence on Wind Energy Converters sponsorizzato dal Center for Wind Energy Research dove sono state discusse problematiche riguardanti gli effetti della turbolenza sui processi di produzione dell’energia eolica, sull’efficienza delle wind farm e sul vento generato da strati limite atmosferici
Main instabilities of coaxial jets
No full textTwo coaxial jets which interact and mix belong to the class of flows which are of great interest from
both the research and industrial point of view. They have a simple geometry but still the possibility
to easily change various parameters makes them suitable for studies of different phenomena related to
stability, mixing and turbulence. The definition of the variables able to control the flow dynamics has
high applicative potential because coaxial jets are a prototype of many industrial burners but, on the
other hand, they are simple enough to be experimentally characterized in laboratory. Due to the high
number of parameters able to influence the flow evolution, a complete characterization of such flow is still
missing and, therefore, motivates this paper.
An experimental analysis of the dominant instabilities in the near field of two coaxial jets has been
performed in order to determine the leading processes which start the transition from the initial laminar
state, where the two streams are segregated, to the turbulent state. Different inner/outer jet velocity pairs
(Ui,Uo) have been tested in order to investigate the effect of both velocity ratio ru = Uo/Ui and Reynolds
number. Three main instabilities have emerged depending on the velocity ratio as can be appreciated from
figure 1(a) where isocontours of the dominant frequencies have been plotted. For ru < 0.75, the coaxial
jets dynamics are driven by the inner shear layer instability, in agreement with [1]. For ru > 1.6, the
outer shear layer dominates the near field vortex dynamics [2, 3] while, for ru nearly unitary (i.e. where
0.75 < ru < 1.6), the vortex shedding behind the separating wall imposes its own dynamics [4]. The
latter phenomenon is clearly shown in figure 1(b) where a flow visualization of the near field at ru = 1 is
reported. Behind the inner separating wall there is a flow pattern composed by staggered vortices which
influence the dynamics of the outer shear layer too.
An improved scaling relationship for the Strouhal number StŒ
tx is proposed in order to calculate the
shedding frequency inside the intermediate velocity ratio region. This relationship takes into account
Reynolds number as well as velocity ratio effects and leads to a constant Strouhal number value in the
whole region where vortex shedding is observable, as showed in figure 2.
The present paper confirms experimentally the theoretical results of [5], who proposed that the wake
behind the separation wall between the two streams of two coaxial jets creates the conditions for an
absolute instability. Evidences of the dominance of the vortex shedding phenomenon in the whole near
field inside a certain range of velocity ratios will be presented in the paper. The characterization of this
operating region is of utmost importance because the vortex shedding provides a continuous passive forcing
mechanism for the control of the flow field, opposite to conventional strategies which use active methods
focused to control the outer shear layer dynamics [3]. Therefore, these results allow many improvements
in the industrial geometries where coaxial jets are employed by means of just a proper choice of the exit
geometry
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
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