Phase appearance or disappearance in two-phase flows

This paper is devoted to the treatment of specific numerical problems which appear when phase appearance or disappearance occurs in models of two-phase flows. Such models have crucial importance in many industrial areas such as nuclear power plant safety studies. In this paper, two outstanding problems are identified: first, the loss of hyperbolicity of the system when a phase appears or disappears and second, the lack of positivity of standard shock capturing schemes such as the Roe scheme. After an asymptotic study of the model, this paper proposes accurate and robust numerical methods adapted to the simulation of phase appearance or disappearance. Polynomial solvers are developed to avoid the use of eigenvectors which are needed in usual shock capturing schemes, and a method based on an adaptive numerical diffusion is designed to treat the positivity problems. An alternate method, based on the use of the hyperbolic tangent function instead of a polynomial, is also considered. Numerical results are presented which demonstrate the efficiency of the proposed solutions

The adsorption behaviour of isobutane on Pt(533): A combined RAIRS and TPD study

The adsorption of isobutane on a Pt(533) stepped surface has been investigated using temperature programmed desorption (TPD) and reflection absorption infrared spectroscopy (RAIRS). Isobutane exists in two monolayer states and one multilayer phase on the Pt(533) surface. The most stable desorption state is caused by isobutane desorbing from the terrace planes. The orientation of isobutane in this state was determined from RAIRS measurements. The second monolayer phase probably belongs to isobutane molecules with only two hydrogen atoms in direct contact with the surface. RAIRS spectra also showed there was little bond weakening due to metal adsorbate interaction

Étude palynologique du Dévonien terminal et du Carbonifère inférieur du bassin d'Illizi (Fort-Polignac), Algérie

L'étude de la microflore des formations Djebel llleréne, Issendjel, Assekaïfaf, Oubarakat et El Adeb Larache du bassin d'Illizi (Sahara algérien) a permis d'établir, depuis le Dévonien terminal jusqu au Namurien, six palynozones. Une comparaison est faite avec les travaux de Lanzoni et Magloire et de Massa et al. (bassin de Rhadamès, Libye occidentale)

Age oí the so called "Transitional beds" between Permian and Jurassic formations in the Gijón Area (Asturias, NW Spain)

Palynological study of black marls below the Jurassic doldmltic limestones (Gijdn Formation) in the Gijdn Area (Asturias, NW Spain) show them to be of Rhetian (late Triassic) age. It appears that the so-called "transitional beds" (black arid red marls, sandstones and gypsum) between the Jurassic liiihestones and underlying Permian red-beds are in non-sequence with the latte

Finite Volume Solution of 2D and 3D Euler and Navier-Stokes Equations

This contribution deals with the modern finite volume schemes solving the Euler and Navier-Stokes equations for transonic flow problems. We will mention the TVD theory for first order and higher order schemes and some numerical examples obtained by 2D central and upwind schemes for 2D transonic flows in the GAMM channel or through the SE 1050 turbine cascade of Skoda Plzen. In the next part two new 2D finite volume schemes are presented. Explicit composite scheme on a structured triangular mesh and implicit scheme realized on a general unstructured mesh. Both schemes are used for the solution of inviscid transonic flows in the GAMM channel and the implicit scheme also for the flows through the SE 1050 turbine cascade using both triangular and quadrilateral meshes. For the case of the flows through the SE 1050 turbine we compare the numerical results with the experiment. The TVD MacCormack method as well as a finite volume composite scheme are extended to a 3D method for solving flows through channels and turbine cascades. 1. Mathematical model We consider the system of 2D Navier-Stokes equations for compressible medium in conservative form: W t + F x +G y = R x + S y , W = [#, #u, #v, e], p = (# #(u F = [#u, #u + p, #uv, (e + p)u], G = [#v, #uv, #v + p, (e + p)v], R = [0, # 11 , # 12 , u# 11 + v# 12 + kT x ], S = [0, # 21 , # 22 , u# 21 + v# 22 + kT y ], (1) where # is the density, (u, v) the velocity vector, e the total energy per unit volume, the viscosity coe#cient, k is the heat conductivity, p is the pressure, # is the adiabatic coe#cient, and the components of the stress tensor # are # 11 = u x , # 21 = # 12 = (u y + v x ) , # 22 = u x + 4 . (2) The 2D Euler equations are obtained from the Navier-Stokes equations by..

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