1,720,966 research outputs found
Numerical Simulation of Non-reacting Ducted Fuel Injection by Means of the Diffuse-Interface Σ-Y Atomization Model
No full textA Study on Accounting for Drift Velocities on Liquid Jets Injected in Cross Flow
No full textThe efficiency and combustion performance of propulsion systems, like internal combustion (IC) engines and gas turbines, is known to be related to the performance of the fuel and air mixing process. Operating conditions and fuels are rapidly changing, therefore new CFD models which accurately accounts for all physical aspects, still maintaining a simple framework, are extremely important. In this work we consider the drift velocity contribution, which often is overlooked or neglected, defined as the velocity of the dispersed phase relative to the mixture volumetric mean velocity in a single fluid formulation, a key variable in two-phase mixture model. Water test cases are here considered for the study. The present work investigates the structure and the droplet velocity field of a plain liquid jet injected into a high-pressure air crossflow. Because of the large scale separation between the small features of the interface and the overall jet we use the diffuse-interface treatment in a single-fluid Eulerian framework. A ς- Y family model is implemented in the OpenFOAM framework which includes liquid diffusion due to drift-flux velocities and a new formulation of the spray atomization. The main objective is to explore the droplet velocity distribution and the jet structure with and without considering the drift flux correction and compare the related results with the experimental data
Lagrangian CFD modeling of ammonia sprays: A correlation across flash boiling and evaporative conditions
No full textSimulations of liquid ammonia spray are performed for different ambient pressures to investigate the transition between flash-boiling and non-flashing regimes, through Computational Fluid Dynamics (CFD). The Lagrangian particle method, within the Reynolds Averaged Navier Stokes (RANS) approach for turbulence is used. Numerical results are compared with experimental liquid and vapor tip penetrations, spray morphology and Sauter Mean Diameter (SMD) measurements, for a multi-hole injector. An adaptation of Kelvin-Helmholtz - Rayleigh-Taylor (KH-RT) breakup model constants and prescribed jet cone angle is necessary for each regime, as standard values used for traditional fuels, e.g., gasoline, appear not to work with ammonia. Capturing local spray details and SMD values across all regimes with a single model setup is very challenging, especially with a new fuel such as ammonia, whose properties differ by a large amount from more established values for hydrocarbons. In this study a correlation for ammonia is proposed for the KH-RT breakup model constants and jet cone angle as a function of operating conditions across flash-boiling and non-flashing regimes. In addition, local temperature predictions are extensively discussed, for both liquid and gaseous phases, highlighting and quantifying the strong cooling effect that ammonia produces during the phase change process
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
Development of a drift-flux velocity closure for a coupled Σ-Y spray atomization model
No full textModeling of spray in a dense near-nozzle region remains a great challenge, because of the large scale separation between the small features of the interface and the overall jet. Diffuse-interface treatment in a single-fluid Eulerian framework, in which the interfacial surface area density (Σ) is used to describe the atomization process, has attracted interest for its potential in providing a manageable and still accurate model. In this work, we propose a new formulation of the Σ-Y spray atomization model that accounts for liquid diffusion due to drift-flux velocities, correctly predicting the behavior under all relevant engine conditions. Additionally, the present formulation allows the interfacial dynamics to impact the transport of the liquid mass fraction, thus making the interfacial density an active scalar fully coupled with the rest of the flow, overcoming limitations of previous formulations. The new model is implemented in the OpenFOAM framework and validated against experimental measurements under non-vaporizing and vaporizing environments, and at reacting conditions
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
LES investigation of cycle-to-cycle variation in a SI optical access engine using TFM-AMR combustion model
No full textMulti-cycle large-eddy simulations (LES) are performed to investigate combustion cycle-to-cycle variability (CCV) in a gasoline spark ignited optical access engine operating under homogeneous stoichiometric conditions. Combustion is addressed with the Thickened Flame Model (TFM) and finite rate chemistry is accounted for through a reduced oxidation reaction mechanism. In view of the fact that computational costs of LES engine simulations are still very high today, this work investigates the use of adaptive mesh refinement (AMR) in the flame zone in conjunction with the artificial flame thickening applied by the TFM model. The paper discusses how the resulting coupled TFM-AMR combustion model allows good resolution of the flame, maintaining accuracy at acceptable costs. First, the details of the coupled model are presented and the effects of the parameters are explored, highlighting their impact on the combustion prediction. Then, computational fluid dynamics (CFD) simulation results are validated against experimental data collected in a low-speed low-load engine point, by comparing 20 LES cycles and 100 measured cycles, for mass fraction burned, combustion phasing, flame images and CCV indices. Lastly, a detailed investigation on the fastest and slowest numerical cycles is presented, analyzing instantaneous flame structures, ignition behaviors, propagation speeds, and probability density function (PDF) of the instantaneous velocity fluctuation around the spark region. The results show that combustion variability is highly correlated to the resolved velocity field and the resolved turbulence intensity, which is found to be the main cause of CCV and affects the early flame kernel growth. This work is an early attempt to use TFM-AMR combustion model for LES simulations of internal combustion engines
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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