1,720,958 research outputs found
Interaction of separation and transition in laminar separation bubbles in a 3D boundary layer
No full textThe influence of different disturbance combinations and increasing sweep on a family of pressure-induced laminar separation bubbles is studied systematically by means of direct numerical simulation (DNS). Three types of disturbance waves are tested against their potential to stimulate the growth of background disturbances of fundamental or subharmonic frequency. The focus is on 2D-disturbances, which are normally the most amplified disturbances in unswept separation bubbles. For the present 3D-base flows, they are found to lose their dominance for sweep angles larger than 10° to 15°. Instead, oblique waves with a propagation direction between 0° and -6° relative to the potential streamline trigger the strongest growth of background disturbances. Spatial linear stability theory (LST) was utilised to select the mosta mplified disturbances for each sweep angle. LST turned out to be as reliable as in unswept laminar separation bubbles and its excellent agreement with DNS within the linear domain was not adversely affected by the sweep angle
The effect of sweep on laminar separation bubbles
No full textThe effect of a systematic variation of the sweep angle on the disturbance amplification and onset of transition is studied in a generic family of swept laminar separation bubbles (LSB) by means of direct numerical simulation. The detailed analysis of a transition scenario with fundamental resonance in a 30°-LSB shows, that the saturation of background disturbances is the key
event, after which a rapid breakdown of transitional structures to smaller scales and thus turbulent flow occurs. The stages of transition are similar to unswept LSB, but two-dimensional disturbances lose their dominance for sweep angles larger than 15°. Instead, oblique Tollmien-Schlichting waves which travel approximately along the direction of the potential streamline
experience the maximal amplification in the linear stage and stimulate the strongest growth of background disturbances after saturation
Applicability and quality of linear stability theory and linear PSE in swept laminar separation bubbles
No full textFast numerical evaluation of flow fields with vortex cells
Full text linkA vortex cell (in this paper) is an aerodynamically shaped cavity in the surface of a body, for example a wing, designed specially to trap the separated vortex within it, thus preventing large-scale unsteady vortex shedding from the wing. Vortex stabilisation can be achieved either by the special geometry, as has already been done experimentally, or by a system of active control. In realistic conditions the boundary and mixing layers in the vortex cell are always turbulent. In the present study a model for calculating the flow in a vortex cell was obtained by replacing the laminar viscosity with the turbulent viscosity in the known high-Reynolds-number asymptotic theory of steady laminar flows in vortex cells. The model was implemented numerically and was shown to be faster than solving the Reynolds-aver- aged Navier–Stokes equations. An experimental facility with a vortex cell was built and experiments performed. Comparisons of the experimental results with the predictions of the model are reasonably satisfactory. The results also indicate that at least for flows in near-circular vortex cells it is sufficient to have accurate turbulence models only in thin viscous layers, while outside the viscosity should only be small enough to make the flow effectively invisci
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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