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Numerical Simulations of Turbulent Helical Flow in a Ranque-Hilsch Vortex Tube with different RANS closures and Sub-Grid Scales Models
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Numerical analysis of compressible turbulent helical flow in a Ranque-Hilsch vortex-tube
No full textNumerical analysis of the internal flow field in a Ranque-Hilsch vortex tube (RHVT) has been conducted in order to improve understanding of its fluid-dynamic behaviour. The flow field in an RHVT is compressible, turbulent and helical with a very high degree of swirl; hence its numerical simulation is a challenging task. Particular interest has been reserved for turbulence modelling, hence both RANS and LES approaches have been employed. In particular axial-symmetric RANS simulations have been conducted using RNG k-epsilon and a linear RSM (Reynolds Stress differential Model) closure models, while full three-dimensional LESS have been performed using Smagorinsky and Germano-Lilly sub-grid scales (SGS) models. Results showed, that turbulence closure models choice is a crucial issue in the prediction of the flow field in an RHVT. In fact, different simulations exhibit some differences in the description of the velocity vector components. In each simulation, flow government equations have been solved using the commercial finite volume code FLUEN (TM) 6.3.26.
Flow patterns in this device have been also investigated by means of the calculation of the Helical Flow Index or normalized helicity; Power Spectral Density (PSD) of velocity magnitude has been eventually calculated showing a good agreement with K41 theory. An improved understanding of the flow field inside the RHVT can lead to a correct prediction of fluid dynamic and thermal behaviour of outlet jets, fundamental information to define cooling performance of this device
Numerical simulation of turbulent flow in a Ranque-Hilsch vortex tube
No full textThe present work is about numerical simulations of the internal flow in a commercial model of a Ranque– Hilsch vortex tube (RHVT) operating in jet impingement. Simulation of the turbulent, compressible, high swirling flow was performed by both RANS and LES techniques. The effect of different turbulence closure models have been tested in RANS simulations using a first order closure RNG k–e and, for the first time in this kind of flow, a second order RSM (Reynolds Stress differential Model) closure. RANS computations have been executed on an axis-symmetric two-dimensional mesh and results have been compared with LES ones, obtained over a three-dimensional computational grid. Smagorinsky sub-grid scale model was used in LES. All the calculations were performed using FLUENTTM 6.3.26. The use of a common code for the different simulations allowed the comparison of the performances of the different techniques and turbu- lence models, avoiding the introduction of other variables.
In all the simulations performed, consistency with the real commercial vortex tube model in jet impingement operation has been followed by substituting an axial hot computational exit to the usual radial one. Comparison of the results between RANS simulations performed on both a traditional radial hot outlet computational domain and one with an axial hot outlet, demonstrates the suitability of the computational model adopted in this work, closer to the real geometry of the device, particularly in RANS RSM simulations. Results in different sections of the tube show significant differences in the velocity pro- files, temperature profiles and secondary vortex structures, varying turbulence model.
The accurate numerical simulation of the flow in a RHVT, resulting in an improved prediction capability of the kinematic and thermal properties of outgoing jets, could allow a correct estimation of the cooling performance of this device in jet impingement operation
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
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