1,355,157 research outputs found
Todor Krastev – A Life Dedicated to the Geomorphology and Geology of Eastern Bulgaria and Black Sea
No full textThe article is dedicate to the life and the creation of one notable Bulgrian investigator, scientist and pedagogue – Prof. Todor Ivanov Krastev DSc (Geography). The principal features of his personality are the big creative energy, impressive capacity for work and restless research spirit. It worldly and creative way is a splendid example for a dedicated work for the science. The results of Prof. Krastev investigations belong to the most Bulgarian Natural Geography achievements for the second part of the twenty century
Validation of a zonal hybrid URANS/LES turbulence modeling method for multi-cycle engine flow simulation
No full textA zonal hybridization of the RNG (Formula presented.) - (Formula presented.) URANS model is proposed for the simulation of turbulent flows in internal combustion engines. The hybrid formulation is able to act as URANS, DES or LES in different zones of the computational domain, which are explicitly set by the user. The resulting model has been implemented in a commercial computational fluid dynamics code and the LES branch of the modified RNG (Formula presented.) - (Formula presented.) closure has been initially calibrated on a standard homogeneous turbulence box case. Subsequently, the full zonal formulation has been tested on a fixed intake valve geometry, including comparisons with third-party experimental data. The core of the work is represented by a multi-cycle analysis of the TCC-III experimental engine configuration, which has been compared with the experiments and with prior full-LES computational studies. The applicability of the hybrid turbulence model to internal combustion engine flows is demonstrated, and PIV-like flow statistics quantitatively validate the model performance. This study shows a pioneering application of zonal hybrid models in engine-relevant simulation campaigns, emphasizing the relevance of hybrid models for turbulent engine flows
Simulating Engineering Flows through Complex Porous Media via the Lattice Boltzmann Method
No full textIn this paper, recent achievements in the application of the lattice Boltzmann method (LBM) to complex fluid flows are reported. More specifically, we focus on flows through reactive porous media, such as the flow through the substrate of a selective catalytic reactor (SCR) for the reduction of gaseous pollutants in the automotive field; pulsed-flow analysis through heterogeneous catalyst architectures; and transport and electro-chemical phenomena in microbial fuel cells (MFC) for novel waste-to-energy applications. To the authors’ knowledge, this is the first known application of LBM modeling to the study of MFCs, which represents by itself a highly innovative and challenging research area. The results discussed here essentially confirm the capabilities of the LBM approach as a flexible and accurate computational tool for the simulation of complex multi-physics phenomena of scientific and technological interest, across physical scales
Asymmetric water impact of a two dimensional wedge: A systematic numerical study with transition to ventilating flow conditions
No full textVessels and other marine structures are frequently subject to intense loads deriving from water impact under various conditions. Such forces influence both the structural resistance and the maneuvering capabilities of boats. Water impacts are also relevant in other fields, such as civil engineering, energy harvesting, and aerospace engineering.In this paper we numerically investigate the hydrodynamics related to the asymmetric water impact of a two dimensional wedge shape. We study the combined effects of geometrical and kinematic asymmetry by systematically varying the wedge roll angle and the direction of the impact velocity. The Volume Of Fluid (VOF) is utilized to model the free surface flow. The numerical model is validated against independent experimental data available in the literature.The results provided evidence the capabilities of multidimensional modeling in predicting global hydrodynamics and local fluid dynamics features of asymmetric impacts. Moreover, we demonstrate the importance of some fundamental methodological aspects, such as the correct initialization of the computational domain. The role of kinematic asymmetry in flow ventilation occurrence is also clearly highlighted. Our results are expected to facilitate the development of analytical and semi-analytical models and to offer guidelines for conducting experiments and parametric studies for the design of marine vessels
Effects of the Domain Zonal Decomposition on the Hybrid URANS/LES Modeling of the TCC-III Motored Engine Flow
No full textHybrid URANS/LES turbulence modeling is rapidly emerging as a valuable complement to standard LES for full-engine multi-cycle simulation. Among the available approaches, zonal hybrids are potentially attractive due to the possibility of clearly identify URANS and LES zones, eventually introducing further zone types with dynamically switching behavior. The present work aims at evaluating the impact of different zonal configurations on the simulated flow statistics using the well-assessed TCC-III experimental engine setup. More specifically, different methods (URANS, LES or seamless DES) are applied inside the cylinder volume, as well as into the intake/exhaust ports and plenums. For each of the five tested configurations, in-cylinder flow features are compared against the reference TCC-III experimental measurements, in terms of velocity field statistics and quality indices. In addition, a detailed analysis using Proper Orthogonal Decomposition (POD) is carried out to quantitatively compare the results from experiments and simulation sets. The study outcomes are used as a starting point for discussing the applicability of zonal hybrid turbulence modeling to realistic engine geometries, critically analyze the model assumptions (e.g. the domain zonal decomposition) and provide guidelines for general application of such method
The Post-Political Democracy of the Distrustful: Commentary on Essays by Ivan Krastev
No full textIn his essays, collected in In Mistrust We Trust: Can Democracy Survive When We Don’t Trust Our Leaders? and Democracy Disrupted: The Politics of Global Protest, Ivan Krastev questions the state of contemporary democracy. He describes it as ‘post-political’ because while procedures are observed, democratic elections take place, and governments are sometimes replaced, nothing of substance changes in politics and voters lack any sense of having influence or that their votes actually matter. Democracy is obviously in crisis and a variety of solutions to this predicament have been proposed: even more elections more direct democracy, or more transparency. Or perhaps a remedy to the crisis of democracy will stem from protests and from ‘taking to the streets’—these being ‘alternate means’ of doing politics? Krastev criticizes all the above proposals, concluding that none is satisfactory or likely to restore trust in democratic institutions. Perhaps democracy ought not to be superficially improved, but instead rethought from the be ginning? The author points to several questions that should be taken into account in thinking about a new form of democracy. She also considers whether the mass protests of the 2010s were a new phenomenon and involved new ideas for doing politics, or were typical modern social movements, only on a global scale and employing novel instruments of mobilization
Numerical simulation of MFC performance: a Lattice Boltzmann study
No full textIn this work, a novel numerical approach is proposed for the simulation of electrochemical and power performance of Microbial Fuel Cells (MFC). Our model is based on the Lattice Boltzmann Method, a numerical approach based on an optimized formulation of Boltzmann's Kinetic Equation, which has been successfully applied to phenomena of technical and engineering interest in recent years. Employing a multi-component LBM solver, an accurate prediction of species transport and electrochemical reactions is achieved inside the reactor chamber. The direct conversion of organic substrate into e− and H+ as by-products of microbes metabolism has been modeled according to previous experimental activity. The physical and electrochemical characteristics of anode and cathode electrodes have been accounted for and their effects on internal species transport and charge transfer is accurately simulated. The good agreement between our results and the experiments in literature highlight the reliability and versatility of LBM to predict the performance of MFCs and to shed light on the complex phenomena occurring inside the reactors
On the detailed multidimensional modeling of HT PEM fuell cells and stacks
No full textA detailed multidimensional CFD-electrochemical model of a single HT PEM fuel cell has been firstly developed, in order to assess its reliability as an engineering simulation tool for HT PEM based energy systems. The model performances have been validated against ad hoc experimental measurements made on a single HT PEM cell, including different anode gas compositions (either pure H-2 or Syngas).In a second stage, a reduced single cell model has been derived from the fully detailed configuration, with the aim of evaluating its feasibility in HT PEM stack performance predictions. The reduced model was then replicated for the reproduction of a mini-stack configuration, carrying out some preliminary simulations on the latter
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