An interface-capturing method for incompressible two-phase flows. Validation and application to bubble dynamics

We report on the development and applications of an interface-capturing method aimed at computing three-dimensional incompressible two-phase flows involving high density and viscosity ratios, together with capillary effects. The numerical approach borrows some features to the Volume of Fluid method (since it is essentially based on the transport of the local volume fraction of the liquid) as well as to the Level Set technique (as no explicit reconstruction of the interface is carried out). The transport of the volume fraction is achieved by using a flux-limiting Zalesak scheme and the fronts are prevented from spreading in time by a specific strategy in which the velocity at nodes crossed by the interface is modified to keep the thickness of the transition region constant. As shown on several test cases, this algorithm allows the interface to deform properly while maintaining the numerical thickness of the transition region within three computational cells whatever the structure of the local flow field. The full set of governing equations is then used to investigate some fundamental aspects of bubble dynamics. More precisely we focus on the evolution of shape and rise velocity of a single bubble over a wide range of physical parameters and on head-on and side-by-side interactions between two rising bubbles.     

Uniformly valid approximation for channel flowApproximation valable uniformément pour l'écoulement dans un canal

The flow at high Reynolds number in a two-dimensional channel whose walls are slightly deformed is considered. This Note addresses the problem of constructing a uniformly valid approximation leading to a better understanding of two-dimensional steady laminar incompressible separated flow. It is proposed to use a new asymptotic approach: the Successive Complementary Expansions Method (SCEM). The starting point is an assumed form of the approximation. The matching principle is a by-product of the method not at all necessary to construct the uniformly valid approximation. To cite this article: J. Mauss et al., C. R. Mecanique 334 (2006).     

Présentation d'une méthode d'étude de la stabilité linéaire d'écoulements instationnairesPresentation of a method for linear stability analysis of unsteady flow

We propose a linear stability analysis of unsteady viscous flow. We apply this method to an oscillatory pipe flow with an axisymetric 2D perturbation which has received considerable attention. The numerical results are relevant. To cite this article: M. Siouffi et al., C. R. Mecanique 330 (2002) 641–645.     

Écoulement de Couette Taylor diphasiqueTwo phase Couette Taylor flow

This paper presents the study of mutual interactions between dispersed and continuous phase in Couette Taylor flow. The introduction of the dispersed phase is obtained by ventilation or by pressure drop in an airtight chamber. In the first instabilities, the dispersed phase generate a modification of the flow state, the cavitating flow being moreover characterised by an advance to the third instability. The dispersed phase first stands along each of the apparent azimuthal waves as a string of individual bubbles located near the core of the Taylor cells and then migrates to the outflow regions near the inner cylinder. To cite this article: H. Djéridi et al., C. R. Mecanique 330 (2002) 113–119.     

基于径向剪切干涉仪的三维位移测量技术

本文提出一种基于双圆光栅径向剪切干涉仪的三维位移测量方法,其测量原理是径向剪切干涉仪所形成的莫尔条纹不仅由二维平面内位移决定,轴向位移会在+1和–1级莫尔条纹之间产生一个特定的相移.首先,基于标量衍射理论对双圆光栅径向剪切干涉仪的+1和–1级莫尔条纹强度分布进行推导,建立了三维位移量与莫尔条纹强度分布的精确解析关系;其次,在频谱分析的基础上,利用半圆环滤波器进行空间滤波,实现+1和–1级莫尔条纹的同时成像;然后,提出了从莫尔条纹图中定量提取三维位移的算法,并通过数值模拟进行验证;最后,实验结果验证了该方法测量平面内位移的最大绝对误差为4.8×10^–3 mm,平均误差为2.0×10^–4 mm,轴向位移的最大绝对误差为0.25 mm,平均误差为8.6×10^–3 mm.该方法具有装置简单、测量精度高、非接触、瞬时测量等特点,可实现三维位移的同时测量.     

A fast and practical method to pack spheres for mesh generation

Sphere packing is an attractive way to generate high quality mesh. Several algorithms have been proposed in this topic, however these algorithms are not sufficiently fast for large scale problems. The paper presents an efficient sphere packing algorithm which is much faster and appears to be the most practical among all sphere packing methods presented so far for mesh generation. The algorithm packs spheres inside a domain using advancing front method. High efficiency has resulted from a concept of 4R measure, which localizes all the computations involved in the whole sphere packing process.     

指数函数的二次Padé逼近的构造

本文通过e- x的Padé逼近构造e- x的一般二次Padé逼近.     

Numerical simulation of dust explosions in pneumatic conveyors

Dust conveyors are used in a wide range of industrial applications. Explosions can be transmitted through dust conveyors to different parts of a processing facility and thus can cause a large amount of damage. In order to study the evolution of dust explosions in such conveyors, a numerical model was developed which combines a front tracking method with a solver for the Euler equations. In this model the effects of the chemical reactions and of the flow turbulence were summarized in the turbulent burning velocity of the dust-air mixture. This approach results in a large reduction of the computational effort and thus allows to study the influence of parameter variations. Here results are presented for corn starch-air mixtures. The numerical model was first calibrated by comparison with one set of experimental data. The model was then tested by comparison with different experimental data and the sensitivity of the model parameters is discussed. Finally calculations were performed for different dust concentrations, flow velocities and tube lengths. Received: 5 July 1997 / Accepted 21 July 1998     

基于亚波长光栅结构的硅基液晶器件模型研究

金(Au)亚波长光栅被溅射到经典硅基液晶(LCoS)的ITO电极上,它与薄液晶盒和底层铝电极组成复合共振波导结构,简称GLCoS。与基于液晶传播效应的LCoS截然不同,在GLCoS中,上电极的表面等离激元与光栅槽中的TM-FP (TM-Fabry Pérot)共振耦合,诱导一个0阶反射的相位调制;铝(Al)电极既是反射背板又与Au光栅、薄液晶盒组成波导,使共振耦合得到增强。在操控光波阵面的同时,GLCoS也作为电控器件,施加电压改变液晶的折射率,进而控制开腔FP的边缘介质条件,达到有源0~2π相位调制。实验结果表明,本文结构可用于1μm量级像素的相位空间光调制器,在高空间带宽积的全息视频显示中具有广阔的应用前景。     

补偿Lévy流的实践稳定性

本文的目的是讨论补偿Ｌéｖｙ流的实践稳定性问题．我们推广了一些微分不等式,并通过Ｌｙａｐｕｎｏｖ函数与比较原理,得到补偿Ｌéｖｙ流的实践稳定性的若干判据．