1,720,966 research outputs found
Aerodynamic characterization of rolling wheels at high Reynolds numbers
No full textComplex and unstable phenomena, such as large-scale boundary layer separations, recirculation zones, and three-dimensional vortical structures, characterize the flow around rotating cylinders. These phenomena are even more interesting when the cylinder is rolling on a solid surface, like a wheel on the ground, because the knowledge of the unsteady features of the wake matters for the aerodynamic design of race cars. For this purpose, we investigated the flow past an isolated wheel in different configurations. We focus on the effect of the aspect ratio and the Reynolds number on the wake for values that reflect the actual operating conditions for a race car. We validated our Detached-Eddy simulation by comparing the results with particle image velocimetry measurements. Then, we analyzed the flow by exploiting proper orthogonal decomposition to identify the turbulence characteristics. The simulation showed excellent agreement with the available experimental data and helped highlight the physics of the wake downstream rolling wheels in different operating conditions
Under-Expanded Jets in Advanced Propulsion Systems—A Review of Latest Theoretical and Experimental Research Activities
Full text linkThe current ongoing rise in environmental pollution is leading research efforts toward the adoption of propulsion systems powered by gaseous fuels like hydrogen, methane, e-fuels, etc. Although gaseous fuels have been used in several types of propulsion systems, there are still many aspects that can be improved and require further study. For this reason, we considered it important to provide a review of the latest research topics, with a particular focus on the injection process. In advanced engine systems, fuel supply is achieved via enhanced direct injection into the combustion chamber. The latter involves the presence of under-expanded jets. Under-expanded jets are a particular kind of compressible flow. For this reason, the review initially provides a brief physical explanation of them. Next, experimental and numerical CFD investigation techniques are discussed. The last section of this manuscript presents an analysis of the jet’s structure. The injection parameters commonly used are examined; next, the characteristics of the near-nozzle field are reviewed and finally, the far-field turbulent mixing, which strongly affects the air–fuel mixture formation process, is discussed
Gasoline direct injection engines – A review of latest technologies and trends. Part 1: Spray breakup process
No full textThe ever more stringent vehicle emissions rules are leading gasoline engine research and development toward the use of direct injection systems. This technology is already present in commercial vehicles, but there are still many aspects that can be improved and need a deeper investigation. For this reason, it was considered important to provide a review of the latest research topics, sorting them as if we are following the ideal life of a fuel droplet, beginning from the injection and ending after the combustion reaction, making available to researchers a tool to understand the state of the art of gasoline direct injection's research and technologies. Spray breakup is the first and crucial process that occurs when the fuel is injected within the combustion chamber, and it is treated extensively and in detail in the literature. In this work, a broad analysis of new mathematical models and experimental imaging techniques, used to study spray breakup and the subsequent impact on the engine surfaces, is reported and commented on. The studies aim at a broader understanding of the phenomena, a better characterisation of the jet, and the final optimisation of the engine design. In a subsequent work (Part 2), a research review on the mixture formation process, combustion and emission characterisation will be addressed
Enabling technologies assessment for reducing Italian LPT emissions on short and long-term time frames
Full text linkThe international policies on energy transition and sustainable development for mitigating global warming aim to limit the rise in global temperatures to 1.5 °C and consequently to outline a transition towards zero greenhouse gas emissions (GHG) by 2050. Vehicular traffic is responsible for about 30% of the total direct GHG, making it one of the most critical sectors. The achievement of net zero GHG emission goal in transportation sector relies in both improving the energy efficiency of the actual vehicles and promoting more efficient modes of transport. In this context, the development and enhancement of local public transport (LPT) systems represent a key point for future mobility, due to the reduced consumption and emissions per unit of transported passenger. As a result, public transport companies need to take rapid action to modernize their fleets, which currently consist mostly of diesel buses, by introducing vehicles and fuels with a lower environmental impact. With reference to the bus transit component of LPT, this article provides an assessment of vehicle and energy enabling technologies for emission mitigation in Italian LPT in a short (2030) and medium-long term (2050) application time frame, in accordance with the EU policy objectives contained in the "Fitfor55" proposal. The study shows that achieving GHG reduction targets requires the use of a mix of technological solutions, both vehicular and energy. Some of them, reduced environmental benefits, are immediately exploitable, in terms of maturity and cost-effectiveness, while others, more promising, are based on less mature technologies, now more expensive, and on the use of energy vectors produced from renewable sources, for which a significant research and development effort is required
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
CFD Numerical Reconstruction of the Flash Boiling Gasoline Spray Morphology
No full textThe numerical reconstruction of the liquid jet generated by a multi-hole injector, operating in flash-boiling conditions, has been developed by means of a Eulerian- Lagrangian CFD code and validated thanks to experimental data collected with schlieren and Mie scattering imaging techniques. The model has been tested with different injection parameters in order to recreate various possible engine thermodynamic conditions. The work carried out is framed in the growing interest present around the gasoline direct-injection systems (GDI). Such technology has been recognized as an effective way to achieve better engine performance and reduced pollutant emissions. High-pressure injectors operating in flashing conditions are demonstrating many advantages in the applications for GDI engines providing a better fuel atomization, a better mixing with the air, a consequent more efficient combustion and, finally, reduced tailpipe emissions
Cartesian mesh generation with local refinement for immersed boundary approaches
Full text linkIn this paper, an efficient and robust Cartesian Mesh Generation with Local Refinement for an Immersed Boundary Approach is proposed, whose key feature is the capability of high Reynolds number simulations by the use of wall function models, bypassing the need for accurate boundary layer discretization. Starting from the discrete manifold model of the object to be analyzed, the proposed model generates Cartesian adaptive grids for a CFD simulation, with minimal user interactions; the most innovative aspect of this approach is that the automatic generation is based on the segmentation of the surfaces enveloping the object to be analyzed. The aim of this paper is to show that this automatic workflow is robust and enables to get quantitative results on geometrically complex configurations such as marine vehicles. To this purpose, the proposed methodology has been applied to the simulation of the flow past a BB2 submarine, discretized by non-uniform grid density. The obtained results are comparable with those obtained by classical body-fitted approaches but with a significant reduction of the time required for the mesh generation
A real-fluid low-dissipative solver for flash boiling simulations of non-equilibrium mixtures
No full textAn Eulerian fluid-dynamic code for simulating compressible, multi-phase flows with phase transition modeling was developed. The code features a low-dissipative flux-splitting discretization scheme, a real-fluid library to properly describe thermophysical properties, and a phase transition model for flows with thermal non-equilibrium. Large Eddy Simulations of the internal and near nozzle flow of a fuel injector were carried out to assess the capabilities of the developed approach. X-ray measurements of iso-octane injections were exploited for validation purposes. Propane injections were then deeply investigated to verify the ability of the mathematical model to represent under-expanded two-phase jets properly. The results provide essential insights on the fluid-dynamic behavior of such two-phase jets, which can also be extended to the injection of alternative fuels like methanol, hydrogen, propane, and in general high-volatility e-fuels
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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