A suitable parametrization to simulate slug flows with the Volume-Of-Fluid method

Diffuse–interface methods, such as the Volume-Of-Fluid method, are often used to simulate complex multiphase flows even if they require significant computation time. Moreover, it can be difficult to simulate some particular two-phase flows such as slug flows with thin liquid films. Suitable parametrization is necessary to provide accuracy and computation speed. Based on a numerical study of slug flows in capillary tubes, we show that it is not trivial to optimize the parametrization of these methods. Some simulation problems described in the literature are directly related to a poor model parametrization, such as an unsuitable discretization scheme or too large time steps. The weak influence of the mesh irregularity is also highlighted. It is shown how to capture accurately thin liquid films with reasonably low computation times

A penalization technique applied to the “Volume-Of-Fluid” method: wettability condition on immersed boundaries

A penalization approach is presented to simulate two-phase flow in the presence of immersed solid boundaries so as to consider highly complex objects such as porous media microstructures. Based on the standard Volume-Of-Fluid formulation, the method takes into account the wettability effects which may occur on the surface of immersed solid boundaries. A spatial shift between the no-slip and the wettability conditions is introduced to make the method stable, regardless of the simulation parameters. The penalized VOF model and the numerical choices are then validated by a series of tests on capillary-dominated flows, which represent the most challenging cases for VOF simulations

A comparison of various methods for the numerical evaluation of porous media permeability tensor from pore-scale geometry

In this work, several boundary value problems used to numerically evaluate the absolute permeability tensors of porous media using core-scale images are compared and discussed. The various configurations differ by the type of boundary conditions used to compute the flow at the micro-scale. The issue is the ability of the method to capture anisotropy correctly and to avoid possible percolation artifacts. This study is carried on two-dimensional synthetic, isotropic or anisotropic, porous media, that are chosen to illustrate the various difficulties mentioned above. A new method is proposed which consists in embedding the porous medium in question in a homogenized one. Using an iterative optimization procedure on the surrounding permeability, the method determines the absolute permeability tensor of the original medium. The equivalent permeability tensor that minimizes the effect on the surrounding porous medium is, unlike that of classical methods, de facto symmetrical due to the use of periodic boundary conditions and exhibits significantly lower permeabilities. The way in which non-diagonal terms of the permeability tensor are obtainedwith the various methods are thoroughly discussed

Critères de stabilité de l'IMPES

L'utilisation de l'algorithme IMPES (IMplicit Pressure - Explicit Saturation) (Sheldon et al. ,1959) pour la simulation d'écoulements multiphasiques en milieux poreux est très courante notamment pour la prédiction de production des champs pétroliers et gaziers. L'IMPES propose une résolution découplée des équations en saturation et pression. Il présente l'avantage de résoudre de manière explicite l'équation en saturation du modèle multiphasique, permettant un gain de temps à la résolution. Cependant, les non-linéarités engendrées par les lois de perméabilités relatives et de pression capillaire associées vont restreindre le domaine de stabilité, faisant émerger plusieurs critères de stabilité spécialisés (Coats et al., 2003; Todd et al., 1972; Aziz et Settari, 1979) dans la littérature au cours des quarante dernières années

Assessment of Solute Transfer Between Static and Dynamic Water During Percolation Through a Solid Leach Bed in Dry Batch Anaerobic Digestion Processes

The aim of this work was to characterize solute transfer between static and dynamic water during percolation through a solid leach bed reactor. A new experimental procedure was set up to measure the solute exchange rate between macro-and micro-porosity. Tracer tests were performed in closed-circuit recirculation experiments. The water behavior was modeled by a multiphase flow model in a double porosity medium using a previously published methodology. The solute exchange rate between static and dynamic water was described by first-order kinetics. The methodology was applied to wheat straw and solid cow manure beds. The solute exchange rate (hs was 0.054 and 0.324 h−1) for wheat straw and solid cow manure, respectively. The measured data was used to improve the prediction capacity of a CFD tool. The results of this work could be used to develop appropriate leachate recirculation strategies to optimize full-scale dry batch anaerobic digestion processes

Pore-network modeling of trickle bed reactors: Pressure drop analysis

A pore network model (PNM) has been developed to simulate gas–liquid trickle flows inside fixed beds of spherical particles. The geometry has been previously built from X-ray micro-tomography experiments, and the flow in the throats between pores is modeled as a pure viscous Poiseuille two-phase flow. The flow distribution between pores and throats is obtained by solving mass and momentum balance equations. As a first application of this simple but powerful meso-scale model, a focus is proposed on the ability of PNM to estimate pressure drop and liquid saturation in co-current gas–liquid flows. PNM results are compared to the classical 1D pressure drop models of Attou et al. (1999), Holub et al. (1992) and Larachi et al. (1991). Agreement and discrepancies are discussed, and, finally, it has been found that the actual PNM approach produces realistic pressure drops as far as inertial contributions to friction are negligible. Concerning liquid saturation, the PNM only estimates its value in the throats between pores. As a consequence, liquid saturations are overestimated, but they can be easily corrected by an ad hoc empirical model

Morfotipos de ammonoideos del Albiense superior de la Cuenca Vasco-Cantábrica: paleoecología y relación con las facies sedimentarias

In this work we present a morphological study of 65 planispiral ammonoid specimens occurring in the stratigraphic succession of the lower upper Albian of the central region of the Basque-Cantabrian Basin, northern Spain. The specimens correspond to the Zones of the ammonoids Hysteroceras varicosum and Mortoniceras inflatum. They are grouped into different morphotypes following the method of “Westerman Morphospace” which suggests diverse habitats for ammonoids, based on shell architecture and shape. The objective of this work is to check the likely correspondence of the suggested habitats with the information given by sedimentology. Accordingly, it has been possible to establish a distribution of the ammonoid ecomorphotypes demersal, nektonic, planktonic and vertical migrant, from shallow (neritic) to deeper marine areas (epipelagic to mesopelagic). The distribution of these ecomorphotypes with different bathimetric affinities is in agreement with the environmental interpretation of sedimentological dataSe han estudiado 65 especímenes de ammonoideos planoespirales de las Zonas de Hysteroceras varicosum y de Mortoniceras inflatum obtenidos de la serie estratigráfica correspondiente a la parte inferior del Albiense superior de la región central de la Cuenca Vasco-Cantábrica, norte de España. Los especímenes se han agrupado en diferentes morfotipos siguiendo su análisis mediante el método de “Westerman Morphospace” , el cual sugiere diversos hábitats para ammonoideos, basado en la arquitectura y forma de la concha. El objetivo de este trabajo es contrastar la posible correspondencia de los hábitats con la información aportada por la sedimentología. De esta manera, se ha podido establecer una distribución de los ecomorfotipos de ammonoideos demersal, nectónico, planctónico y migrante vertical, en áreas marino someras (neríticas) a más profundas (epipelágicas a mesopelágicas). La distribución de estos ecomorfotipos con diferentes afinidades batimétricas se correlaciona de manera bastante precisa con la interpretación ambiental de los datos sedimentológico

A shallow-water cyrtocrinid crinoid (Articulata) from the upper Albian of the Western Pyrenees, North Spain

The cyrtocrinid crinoid Proholopus holopiformis (Remeš, 1902) is described from the upper Albian succession that may be included in the Albeniz unit to the east of Iruñea-Pamplona (Navarre, Western Pyrenees, Spain). Although based on partially disarticulated material, this taxon preserve calyx, stem, attachment structure, and brachial plates from the arms. Proholopus holopiformis was previously described from the Upper Jurassic-Lower Cretaceous of the Czech Republic and Lower Cretaceous of France and Crimea, thus the occurrence from Spain represents the youngest of the species. This allows a better characterization of the family Proholopodidae that was originally described based on calyx morphology only and expands its distribution to the upper Albian. Proholopus holopiformis inhabited the fore-reef areas of coral-sponge bioconstructions. Based on coral types, crinoids are thought to have dwelled near the euphotic-oligophotic zones transition and, thus, thrive in shallow depths. Most specimens have bite marks compatible with cidaroid predation. This represents one of the youngest occurrences of cyrtocrinids inhabiting shallow marine environments before their migration to the deep sea due to the ongoing Mesozoic Marine Revolution