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Mathematical modelling of a two streams coanda effect nozzle
No full textThis paper analyses the ACHEON Coanda effect based propulsion nozzle for aircraft propulsion based on the dynamic equilibrium of two jet streams. It presents a large bibliographic analysis and the ACHEON concept and, in particular, the HOMER Nozzle, that is its main component. The Constructal optimization process that allows defining this architecture has presented. A preliminary mathematical model of a 2D case of the system has presented, focusing on the combined effect of the mixing effect of the two streams and the Coanda Effect Adhesion over a convex surface. A CFD preliminary validation has presented in uncompressible regime. The results have been evaluated in 2D cases
COMPUTATIONAL MODELLING OF LIQUID JET IMPINGEMENT ONTO HEATED SURFACE
No full textQuenching of heated surfaces through impinging liquid jets is of great im-portance for numerous applications like steel processing, nuclear power plants, automobile industries, etc. Therefore, computational modelling of the surface quenching through circular water jets impinging normally onto a heated flat surface has vital importance in order to reveal the physics of the quenching process.
At first, a numerical model was developed for single jet impingement process. A conjugate heat transfer problem was solved implying consideration of both regions, one occupied by fluid (multi-phase flow consisting of water, vapor and ambient air) and one accommodating the solid surface within the same solution domain.
Numerical simulations were performed in a range of relevant operating param-eters: jet velocities (2.5, 5, 7.5 and 10 m/s), water sub-cooling (75 K) and wall-superheat (650 K - 800 K) corresponding closely to those encountered in the industrial water jet cooling banks. Due to the high initial temperature of the surface, the boiling process exhibits strong spatial and temporal fluctuations. Its effect on the boundary layer profiles at the stagnation region at different time intervals are analyzed. The analysis reveals a highly distorted field of both mean flow and turbulence quantities. It represents an im-portant outcome, also with respect to appropriate model improvements. The different boiling characteristics are envisaged in detail to increase the level of understanding of the phenomena. The influence of the turbulent kinetic energy investigated at the boiling front as well as the jet-acceleration region has been studied. The physically relevant results are obtained and analyzed along with reference database provided experimentally by Karwa (2012, ‘Experimental Study of Water Jet Impingement Cooling of Hot Steel Plates,' Dissertation, FG TTD, TU Darmstadt). The intensive quenching process is consistent with the high rate of sub-cooling and high jet velocities. The surface temperature predicted by quenching model within the impingement region and the subsequent wall-jet region agrees reasonably well with the measurements, the outcome being particularly valid at higher jet velocities. However, a steep temperature gradient at the position corresponding to boiling threshold has not been captured under the condition of the numerical grid adopted. On the other hand, a reasonably good prediction of the wetting front propagation phenomena advocates the future development of the model. The high-intensity back motion of the vapor phase in the stagnation region at the earlier times of the water jet impingement can induce an appropriately high turbulence level, which could be accounted well by the turbulence model applied.
The second part of the present work deals with multiple liquid jet impingement. When the multiple jets impact onto the heated surface, the heat flux is extracted from the surface by the mass flow rate. The heat flux is dependent on the several flow conditions and configurations of the nozzle array system. Therefore, one needs to study the nozzle array configuration along with several flow parameters for the better design of the cooling header system. Accordingly, the hydrodynamics of the multiple jets has been studied computationally realizing the need for optimum configuration of the nozzle array. The effects of the mass flow rate, target plate width and the turbulence produced due to the impingement were studied. Afterward, an analytical model is proposed for the quenching of the multiple jets system. It has been realized that, when jet impinges onto the surface at very high initial temperature, the film boiling may play a role in the heat transfer mechanism. Therefore, development has been made in the film-boiling model considering the effect of turbulence at the liquid jet stagnation region at the Leidenfrost point. The Leidenfrost point is the minimum temperature at which the film boiling can sustain. However, the vapor-liquid interface has the dynamic character; it oscillates with high frequency and causes the additional momentum diffusivity. Therefore, the need for introducing the effect of associated turbulence has been felt. The length and velocity scale of the turbulent structure has been approximated by assuming homogeneous turbulence. The new model for the heat flux and wall superheat yielded results agreeing well with published experimental results
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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
Preliminary CDF Assessment of an Innovative Propelled Wing with Enhanced Performances by Coanda Effect
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