1,720,986 research outputs found
The detrimental effect of increasing the number of cameras on self-calibration for tomographic PIV
No full textHeat transfer enhancement of impinging jets with fractal-generated turbulence
No full textA new passive method for the heat transfer enhancement of circular impinging jets is proposed and tested. The method is based on enhancing the mainstream turbulence of impinging jets using square fractal grids, i.e. a grid with a square pattern repeated at increasingly smaller scales. Fractal grids can generate much higher turbulence intensity than regular grids under the same inflow conditions and with similar blockage ratio, at the expense of a slightly larger pressure drop. An experimental investigation on the heat transfer enhancement achieved by impinging jets with fractal turbulence promoters is carried out. The heated-thin foil technique is implemented to measure the spatial distribution of the Nusselt number on the target plate. The heat transfer rates of impinging jets with a regular grid and a fractal grid insert are compared to that of a jet without any turbulator under the same condition of power input. A parametric study on the effect of the Reynolds number, the nozzle-to-plate distance and the position of the insert within the nozzle is carried out. The results show that a fractal turbulence promoter can provide a significant heat transfer enhancement for relatively small nozzle-to-plate separation (for a distance equal to 2 diameters an increase of 63% at the stagnation point, and 25% if averaged over an area of radius equal to 1 nozzle diameter, are respectively found with respect to the circular jet, against 9% and 6% for the regular grid in the same conditions of power input)
On the effect of fractal generated turbulence on the heat transfer of circular impinging jets
No full textThree-dimensional organization of the flow structure in a non-reactive model aero engine lean burn injection system
No full textFlow field topology of impinging jets with fractal inserts
No full textAn experimental investigation of the flow field features of a round air jet equipped with a fractal (FG) and a regular (RG) grid insert impinging on a flat surface is carried out by means of 2D-2C Particle Image Velocimetry (PIV). The results are compared to those for a round jet without any grid (JWT). The test Reynolds number is set to 10, 000. The average flow fields and the turbulent kinetic energy distributions are presented. In particular, the effect of the presence of the fractal grid on the turbulence intensity distribution and on the planar component of the Reynolds stress is analyzed. Some differences between the location of the maximum of the turbulence intensity profile and the data reported in the literature are found. A possible interaction process between the wakes of the grids and the growing shear layer of the jet might be responsible of this discrepancy. A comparison between the flow field and the heat transfer results obtained by the authors in a previous work is also carried out. What is underlined is that both an higher turbulence level and a much stronger axial velocity cause an increment in the heat transfer rate
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
Active Control of Turbulent Convective Heat Transfer with Plasma Actuators
Full text linkWe study an array of streamwise-oriented Dielectric Barrier Discharge (DBD) plasma actuators as an active control technique in turbulent flows. The analysis aims at elucidating the mechanism of interaction between the structures induced by the DBD-plasma actuators and the convective heat transfer process in a fully developed turbulent boundary layer. The employed flush-mounted DBD-plasma actuator array generates pairs of counter-rotating, stationary, streamwise vortices. The full three-dimensional, velocity field is measured with stereoscopic PIV and convective heat transfer at the wall is assessed by infrared thermography. The plasma actuator forcing diverts the main flow, yielding a low-momentum region that grows in the streamwise direction. The suction effect promoted on top of the exposed electrodes confines the vortices in the spanwise direction. Eventually, the pair of streamwise vortices locally reduces the convective heat transfer with a persistence of several outer lengthscales downstream of the actuation.Rodrigo Castellanos, Stefano Discetti and Andrea Ianiro have been supported by the project ARTURO, ref. PID2019-109717RB-I00/AEI/10.13039/501100011033, funded by the Spanish State Research Agency. Theodoros Michelis and Marios Kotsonis are supported by the European Research Council under StG project GloWing (#803082)
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
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