102,438 research outputs found
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
High reynolds number hybrid RANS/LES modeling with turbulent time scale bounding
No full textAn existing two-equation eddy viscosity turbulence model was modified by the authors by application of the normal Reynolds stresses "realizability" constraint to the turbulent time scale τ=k/ε. The model was then sensitized to local grid spacing through relatively straightforward modifications in the k-equation destruction term, obtaining a scale-resolving hybrid RANS/LES formulation. The resulting hybrid form was implemented into an open source finite volume CFD code and evaluated for the resolution of high Reynolds number essentially incompressible flows. The cases studied here include aerodynamic and aeroacoustic predictions for a standard simplified car mirror shape
Hybrid URANS/LES Turbulence Modeling for Spray Simulation: A Computational Study
No full textTurbulence modeling for fuel spray simulation plays a prominent role in the understanding of the flow behavior in Internal Combustion Engines (ICEs). Currently, a lot of research work is actively spent on Large Eddy Simulation (LES) turbulence modeling as a replacement option of standard Reynolds averaged approaches in the Eulerian-Lagrangian spray modeling framework, due to its capability to accurately describe flow-induced spray variability and to the lower dependence of the results on the specific turbulence model and/or modeling coefficients. The introduction of LES poses, however, additional questions related to the implementation/adaptation of spray-related turbulence sources and to the rise of conflicting numerics and grid requirements between the Lagrangian and Eulerian parts of the simulated flow. About the latter, an efficient alternative might be found in hybrid URANS/LES formulations, which are still relatively unexplored for spray modeling applications and for ICE modeling in general. In this work, we conduct a systematic analysis aimed to assess the effects of several URANS, LES and hybrid turbulence modeling formulations on the spray dynamics. The hybrid form is based on a purposely developed version of the k-g URANS closure, and the simulation campaign is focused on a standard n-dodecane evaporating spray case in a constant volume vessel configuration. The spray is modeled within the Eulerian-Lagrangian framework, with primary and secondary breakup taken into account by means of the Kelvin-Helmholtz-Rayleigh-Taylor (KHRT) model. Further, we investigate on the effects due to the Stochastic Turbulence Dispersion (STD) of parcels. Numerical experiments are carried out via the open-source CFD code OpenFOAM. The results are validated against the baseline experimental data for evaporating ECN Spray A and with previous computational findings available in literature
Comparison of enthalpy-porosity and lattice Boltzmann-phase field techniques for the simulation of the heat transfer and melting processes in LHTES devices
No full textThermal energy torage (TES) is a key enabling technology for the efficient exploitation of distributed generation systems based on renewable energy sources. Among the available options, research on latent heat TES (LHTES) solutions has been particularly active in the last decade, due to their ability to store and release high amounts of thermal energy in a very narrow temperature range. LHTES devices are based on phase change materials (PCMs), which act as thermal sinks or sources during their solid-to-liquid transition and vice-versa. As such, the development of reliable numerical tools for the prediction of the heat transfer and phase change characteristics of PCMs is of foremost importance, to help designing innovative and efficiently integrated LHTES implementations. In the present paper, the consolidated enthalpy-porosity (EP) method is compared to a novel lattice Boltzmann-phase field (LB-PF) algorithm in the simulation of a standard numerical benchmark for paraffin-like PCM melting problems. Performances and limitations of the two approaches are discussed, including the influence of model-related and purely numerical parameters. Outcomes from this study are used to confirm general guidelines for the application of well established methodologies, as well as to suggest new pathways for out-of-standard modeling techniques
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
Evaluating the electrochemical and power performances of microbial fuel cells across physical scales: A novel numerical approach
No full textOn 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
On the application of hybrid turbulence models for fuel spray simulation in modern internal combustion engines
No full textIn order to satisfy the increasingly restrictive EU norms on air pollutant emissions, most of the world-leading passenger car manufacturers are currently forced to apply different engine electrification solutions to a large part of their model portfolio, ranging from Mild-Hybrid Electric Vehicles (MEHVs) to Plug-in Hybrid Electric Vehicles (PHEVs). Nonetheless, the efficient design of the thermal engine part still plays a fundamental role in the overall fuel consumption and polluting emissions reduction. Both gasoline-fueled and diesel-fueled modern engines rely on finely tuned direct fuel injection strategies, in order to simultaneously optimize primary energy consumption and particulate matter and/or gaseous emissions. Therefore, it is of foremost importance to develop robust and reliable multidimensional numerical tools, to support engineers during the injection system design and testing processes. In that sense, turbulence modeling is a key point for the accurate description of fuel spray evolution and mixture formation, due to the very high injection pressures (in diesel-fueled engines) or the complex spray patterns and severe flow cyclic variability (in downsized, turbocharged, gasoline-fueled engines). In the present paper, we evaluate the usage of hybrid URANS/LES turbulence modeling techniques for fuel spray simulation, based on the current scientific literature on this topic and on some recent computational studies from the authors. Aspects such as the comparison with URANS and standard LES models are discussed, and strengths and weaknessess of the analyzed hybrid approaches are pointed out. The authors assume that this work could pave the way for further debates on the potential vs. actual benefits of mixing statistically-derived (URANS) and scale-resolving (LES) turbulence modeling options for engine flow simulation
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