Application of a Two-Fluid Model to Simulate the Heating of Two-Phase Flows

International audienceThis paper is dedicated to the simulation of two-phase flows on the basis of a two-fluid model that allows to account for the disequilibrium of velocities, pressures , temperatures and chemical potentials (mass transfer). The numerical simulations are performed using a fractional step method treating separately the convective part of the model and the source terms. The scheme dealing with the convective part of the model follows a Finite Volume approach and is based on a relaxation scheme. In the sequel, a special focus is put on the discretization of the terms that rule the mass transfer. The scheme proposed is a first order implicit scheme and can be verified using an analytical solution. Eventually, a test case of the heating of a mixture of steam and water is presented, which is representative of a steam generator device

Cadophora margaritata sp. nov. and other fungi associated with the longhorn beetles Anoplophora glabripennis and Saperda carcharias in Finland

Symbiosis with microbes is crucial for survival and development of wood-inhabiting longhorn beetles (Coleoptera: Cerambycidae). Thus, knowledge of the endemic fungal associates of insects would facilitate risk assessment in cases where a new invasive pest occupies the same ecological niche. However, the diversity of fungi associated with insects remains poorly understood. The aim of this study was to investigate fungi associated with the native large poplar longhorn beetle (Saperda carcharias) and the recently introduced Asian longhorn beetle (Anoplophora glabripennis) infesting hardwood trees in Finland. We studied the cultivable fungal associates obtained from Populus tremula colonised by S. carcharias, and Betula pendula and Salix caprea infested by A. glabripennis, and compared these to the samples collected from intact wood material. This study detected a number of plant pathogenic and saprotrophic fungi, and species with known potential for enzymatic degradation of wood components. Phylogenetic analyses of the most commonly encountered fungi isolated from the longhorn beetles revealed an association with fungi residing in the Cadophora-Mollisia species complex. A commonly encountered fungus was Cadophora spadicis, a recently described fungus associated with wood-decay. In addition, a novel species of Cadophora, for which the name Cadophora margaritata sp. nov. is provided, was isolated from the colonised wood.Peer reviewe

The coupling of multi-phase flow models

International audienceThis paper provides an overview of some recent developments that were motivated by the unsteady interfacial coupling of existing codes. We describe the framework and the basic ideas first, which mainly rely on the use of a father model. Next we list the main achievements in this domain, and focus then on the interfacial coupling of a three-field model with a two-fluid two-phase flow model. Some numerical results are shown, and we eventually try to point out the main results and give some perspectives for further work

A Mach-sensitive splitting approach for Euler-like systems

Herein, a Mach-sensitive fractional step approach is proposed for Euler-like systems. The key idea is to introduce a time-dependent splitting which dynamically decouples convection from acoustic phenomenon following the fluctuations of the flow Mach number. By doing so, one seeks to maintain the accuracy of the computed solution for all Mach number regimes. Indeed, when the Mach number takes high values, a time-explicit resolution of the overall Euler-like system is entirely performed in one of the present splitting step. On the contrary, in the low-Mach number case, convection is totally separated from the acoustic waves production. Then, by performing an appropriate correction on the acoustic step of the splitting, the numerical diffusion can be significantly reduced. A study made on both convective and acoustic subsystems of the present approach has revealed some key properties as hyperbolicity and positivity of the density and internal energy in the case of an ideal gas thermodynamics. The one-dimensional results made on a wide range of Mach numbers using an ideal and a stiffened gas thermodynamics show that the present approach is as accurate and CPU-consuming as a state of the art Lagrange-Projection-type method

Multidimensional computations of a two-fluid hyperbolic model in a porous medium

International audienceThis paper deals with the computation of two-phase flows in a porous medium, with two main objectives. First of all, we will present a new multi-dimensional well-balanced scheme, with its advantages and draw-backs. Furthermore, we will compare results of the porous model with approximations obtained with a full two-dimensional computation, where all obstacles have been taken into account in the computational domain. The two-phase flow model is hyperbolic, and the scheme takes its roots on a modified Rusanov scheme that integrates effects due to discontinuous porous profiles. The scheme perfectly maintains steady state profiles on any structured mesh

On the Computation of the Baer-Nunziato Model

International audienc

Computing Two-fluid Models of Compressible Water-vapour Flows with Mass Transfer

International audienc