Towards Large Eddy Simulation in Internal-Combustion Engines: Simulation of a Compressed Tumble Flow

Copyright © 2004 SAE International The development of the Large Eddy Simulation (LES) 3D CFD code AVBP to yield a CFD tool able to predict cyclic variability in Internal Combustion (IC) engines is reported. In a first step the implementation of an Arbitrary Lagrangian Eulerian (ALE) method into AVBP is described, allowing to move solid boundaries. Then the principles and implementation of the Conditioned Temporal Interpolation (CTI) mesh management technique is described, and some specific adaptations for LES simulations are discussed. Finally a first validation of the so obtained LES IC engine code is presented by comparing predictions with findings on the square piston experiment

Numerical and experimental studies of the flow around a partially submerged vertical cylinder

International audienceL'écoulement et l'injection d'air autour d'un cylindre vertical partiellement immergé, en translation, est étudié expérimentalement et numériquement. Le régime d'écoulement est turbulent avec 15 000 < Re < 60 000 et 0.4 < F r < 1.7, où Re et F r sont les nombres de Reynolds et de Froude adimensionnés à l'aide du diamètre D du cylindre. Une cavité à l'aval du cylindre est observée. L'objectif de ce travail est d'étudier les efforts de traînée, l'élévation de la surface libre et la vitesse critique à partir de laquelle il y a entraînement d'air. Un bon accord entre les expériences et les simulations a été trouvé, évaluant ainsi la profondeur de la cavité, le coefficient de traînée et la vitesse critique d'injection d'air. Abstract : The flow around a vertical cylinder piercing the free-surface is studied experimentally and numerically. The cylinder has a free-end and the range of velocities are in the regime of turbulent wake with experiments and simulations carried out for 15 000 < Re < 60 000 and 0.4 < F r < 1.7, where Re and F r are the Reynolds and Froude numbers based on the cylinder diameter D. A cavity downstream the cylinder is observed. The focus here is on drag force measurement, free-surface elevation, and critical velocity for air-entrainment. Specifically, a good agreement between experiments and simulations is obtained for the cavity depth, the drag coefficient and the critical velocity

Analyse pour la LES d'une base de données de simulations directes

A Direct Numerical Simulation database of a realistic swirl burner is analyzed to provide novel Large-Eddy Simulation closures. The swirl burner features a flow Reynolds number of 40,000 and a turbulent Reynolds number of 1,400, and is operated with a lean air/methane mixture at a constant flow rate. The DNS is performed with a 2.6-billion cell unstructured mesh that leads to a resolution of 0.1 mm. The LES analysis is carried out from two angles: modeling of flux terms entering the balance equation for the reaction progress variable, and modeling of the subgrid-scale scalar variance

An unstructured conservative level-set algorithm coupled with dynamic mesh adaptation for the computation of liquid-gas flows

International audienceAccurate and efficient simulations of 3D liquid-gas flows are of first importance in many industrial applications, such as fuel injection in aeronautical combustion chambers. In this context, it is mandatory to handle complex geometries. The use of unstructured grids for two-phase flow modeling fulfills this requirement and paves the way to isotropic adaptive mesh refinement. This work presents a narrow-band conservative level-set algorithm implemented in the YALES2 incompressible flow solver, which is combined to dynamic mesh adaptation. This strategy enables resolving the small physical scales at the liquid-gas interface at a moderate cost. It is applied to predicting the outcome of a droplet collision with reflexive separation. In the accurate conservative level set framework, the interface is represented using a hyperbolic tangent profile, which is advected by the fluid, and then reshaped using a reinitialization equation. The classical signed-distance function is reconstructed at nodes in the narrow band around the interface using a geometric projection/marker method (GPMM), to calculate the smallest distance to the interface. The interface normal and curvature are computed using this signed-distance function. Within a mesh cell, the interface is approximated by a segment (2D) or one or several triangles (3D). The distance at the nodes is simply obtained by projection to the closest surface elements. If a node is connected to n elements containing interface fragments, it has a n-marker list (a marker contains the coordinates of the crossing points and the distance). To speed-up the algorithm, the markers stored at each node are sorted based on their distance. Markers are propagated from one band to another: each node compares its markers to its neighbors' and keeps the closest only. The GPMM approach for the reconstruction of the level-set signed-distance function used in conjunction with the reinitialization of Chiodi et al. (2017) leads to significant improvement in the interface quality and overall accuracy compared to the reinitialization of Desjardins et al. (2008) in the calculations performed on unstructured grids. Since the accuracy of the interface normal and curvature directly depends on the signed-distance function reconstruction, less spurious currents occur on the implicit surface. The improved level-set algorithm leads to accurate predictions of the outcome of a droplet collision with reflexive separation, and is validated against the experimental results of Ashgriz et al. (1990). Introduction Two-phase flows are ubiquitous in nature and in industrial systems. The understanding of the various phenomena occurring in liquid-gas flows is crucial for aeronautical combustors, in which a fuel is injected in liquid form, goes under an atomization process, evaporation, mixing with air and eventually combustion. Understanding the atomization process and the resulting droplet distribution is of first importance for aircraft engine performance and operability. The prediction of the atomization process is complex, due to many non-linear phenomena such as interface break-up, droplet convection, or droplet collision. Atomization also involves a wide range of time and space scales, which leads to important calculation costs. Thus, the use of dynamic mesh adaptation for unstructured meshes is particularly helpful for simulating industrial liquid-gas flow problems, as it allows implicit interface dynamics calculation in complex geometries at a reasonable cost [1]. To capture the interface, the conservative level set method is used, which accurately predicts the interface dynamics while conserving liquid mass [2]. This article presents a method to compute the signed-distance function on unstructured grids, and an implementation of the reinitialization of [3], adapted to unstructured meshes. Classic test cases are run to check the overall accuracy and robustness of the method, and a droplet collision case is simulated to validate the global algorithm with a front merging scenario against the experimental results of [4]

Dynamic mesh adaptation for moving fronts and interfaces: application to the modeling of premixed flames and primary atomization

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Etude du développement d'une flamme soumise à un gradient de concentration (Rôle de la stratification et des EGR)

La combustion stratifiée, qui consiste à brûler un mélange carburant/oxydant inhomogène, et la combustion diluée, consistant à ajouter une quantité limitée de gaz brûlés, sont deux technologies utilisées dans les moteurs à piston pour réduire leur consommation. Cette thèse est dédiée à l étude de l allumage dans ces deux types de milieux en régimes laminaire et turbulent. Un nouveau schéma cinétique pour la combustion propane/air a été dérivé et combiné à deux approches de modélisation différentes : la chimie complexe et une approche de chimie tabulée de type FPI. Dans le cas laminaire, les deux approches de modélisation donnent des résultats similaires et un modèle simple a mis en évidence l importance de la dynamique des gaz frais et des gaz brûlés sur le développement du noyau. Dans le cas turbulent, plusieurs techniques d analyse ont montré la dépendance de la vitesse absolue de la flamme au champ de vitesse moyen et la décorrélation des fluctuations locales de richesse.Stratified combustion, which consists in burning an inhomogeneous fuel/air mixture, and diluted combustion, which consists in adding a limited quantity of burnt gases, are two technologies used in internal combustion engines to reduce fuel consumption. This Ph.D is devoted to the study of ignition in these two types of combustion in laminar and turbulent regimes. A new kinetic scheme for propane/air combustion has been derived and combined to two modeling approaches: finite-rate chemistry and an FPI tabulated chemistry approach. In the laminar case, both approaches give similar results and a simplified model has highlighted the importance of fresh and burnt gases dynamics on the kernel development. In the turbulent case, several techniques of analysis have shown the dependency of absolute flame speed on the mean fluid velocity and the lack of correlation to the local equivalence ratio.ROUEN-INSA Madrillet (765752301) / SudocSudocFranceF

Review of electrical energy storage systems in EPS

Diplomsko delo podaja pregled baterijskih sistemov. V uvodu predlagam rešitve, kako izboljšati obratovanje elektroenergetskega sistema s shranjevanjem električne energije. Ker sem se osredotočil na baterije in, da lahko pojasnim, v kakšne namene jih lahko uporabljamo v EES, je potrebno razumeti karakteristike in delovanje baterij ter njihovo tehnologijo. Omenil sem različne uporabe BESS, vendar sem se osredotočil na tri najbolj pogoste probleme, in sicer regulacijo frekvence, regulacijo napetosti in rezanje konic. Predstavil sem tudi največje proizvajalce baterijskih sistemov in njihove projekte.The diploma thesis is a general overview of battery systems. It starts with introduction, which presents how the power system can be improved by storing energy. My focus is on batteries and to better understand batteries and their functions in power system it is necessary to understand the characteristics and the technology of batteries. I mentioned various uses of BESS, but I focused on three most common problems, which are frequency regulation, voltage regulation and peak shaving. Then I introduced largest BESS manufacturers and their biggest projects

Experiments and Simulations of Free-Surface Flow behind a Finite Height Rigid Vertical Cylinder

We present the results of a combined experimental and numerical study of the free-surface flow behind a finite height rigid vertical cylinder. The experiments measure the drag and the wake angle on cylinders of different diameters for a range of velocities corresponding to 30,000 &lt;Re&lt; 200,000 and 0.2&lt;Fr&lt;2 where the Reynolds and Froude numbers are based on the diameter. The three-dimensional large eddy simulations use a conservative level-set method for the air-water interface, thus predicting the pressure, the vorticity, the free-surface elevation and the onset of air entrainment. The deep flow looks like single phase turbulent flow past a cylinder, but close to the free-surface, the interaction between the wall, the free-surface and the flow is taking place, leading to a reduced cylinder drag and the appearance of V-shaped surface wave patterns. For large velocities, vortex shedding is suppressed in a layer region behind the cylinder below the free surface. The wave patterns mostly follow the capillary-gravity theory, which predicts the crest lines cusps. Interestingly, it also indicates the regions of strong elevation fluctuations and the location of air entrainment observed in the experiments. Overall, these new simulation results, drag, wake angle and onset of air entrainment, compare quantitatively with experiments

Simulation of a reactive fluidized bed reactor using CFD/DEM

This report presents the numerical study of a semi-industrial fluidized bed, which involves a reactive fluid phase and an inert granular phase. The simulations are based on a meso-scale approach using the Discrete Element Method (DEM) to represent the Lagrangian phase behavior coupled with Large-Eddy Simulation (LES) for the fluid phase. To cope with the limiting ratio between mesh and particle size stemming from the CFD/DEM modeling, a dynamic thickened flame approach is used. This approach yields interesting results regarding the prediction of the bed critical temperature