Instability in Two-Sided Thermocapillary-Buoyancy Convection with Interfacial

A new model of two-phase thermocapillary-buoyancy convection with phase change at gas-liquid interface in an enclosed cavity subjected to a horizontal temperature gradient is proposed,rather than the previous onesided model without phase change.We study the onset of multicellular convection and two inodes of convective instability,and find four different flow regimes.Their transition map is compared with the non-phase-change condition.Our numerical results show the stabilizing effect of interfacial phase change on the thermocapillarybuoyancy convection.     

大尺度环形液池内双层热毛细对流不稳定性

假设双层流体的交界面不发生变形,热毛细力作用于此交界面,三维数值研究了大尺度环形液池中双层流体系统在内外壁面温差加热下的热毛细对流不稳定性,其中外壁面维持高温,内壁面维持低温。计算结果显示,上下层流体的流动特性受Marangoni效应和浮力效应的影响;热毛细对流的振荡产生于内壁面附近,并沿着温度梯度的方向传播;随着温差的增大,热毛细对流的振荡逐渐增强,温度振荡波数增大。     

PIV技术在气体界面不稳定性实验研究中的应用

采用粒子图像测速(Particle Image Velocimetry,PIV)技术,以乙二醇烟雾作为示踪粒子,实验测量了平面激波作用下SF6气柱-空气界面Richtmyer-Meshkov不稳定性演化图像和二维速度场.测量结果揭示了不稳定性流场的典型特征和细微结构,与高速摄影和数值模拟结果符合,说明建立的PIV技术适...     

The Convection Instability of Bhnard-Rayleigh Fluid Under Varied External Force

A new model of Bknard-Rayleigh convection has been put forward from mantle convection and liquid crystal, where the external force deviates from constant to a lineal function of vertical dimension z. The dimensionless parameter ε is induced to describe the scale of this kind of deviations. Through linear stability analyses, we find that even-odd symmetry broken appears. By numerical calculation under rigid boundary conditions, we find that α_c is almost α constant but R_c decreases nonlinearly as ε increases, so the increase of ε benefits convection. When ε=0, all results reduce to the former works automatically.     

Interfacial Stress,Interfacial Energy,and Phase Equilibria in Binary Alloys

A simple model is presented in order to explore the influence of interfacial stress, interfacial energy, and surface stress on the characteristics of phase equilibria in stressed, two-phase binary alloys. Two different system geometries are employed: concentric spheres and thin plates. The conditions for thermodynamic equilibrium are solved and equations of state for each geometry are obtained in terms of the phase fraction, alloy composition, system dimension, and several dimensionless materials parameters. Elastic stress introduces new equilibrium states that are further modified by the interfacial quantities. Those conditions for which interfacial quantities can induce significant changes in the equilibrium phase fraction and phase compositions are identified.     

一个用于界面不稳定性实验研究的竖式激波管

 研制了一个可用于气-气界面Rayleigh-Taylor（RT）不稳定性、气-液界面Richtmyer-Meshkov（RM）不稳定性、气-液界面RT和RM耦合不稳定性实验的竖式激波管装置,配备了相应的光学电学测量系统,给出了装置的主要技术参数,以及典型实验的压力-时间曲线。利用这套实验装置,可以精确地控制不稳定性的初始扰动界面,观测记录界面演化发展全过程。     

波后滑移线引起的界面变形和R-M不稳定性

实验研究复杂波形结构引起平面界面变形和反射激波冲击下的R-M不稳定性的问题.在竖直激波管中生成稳定的N₂/SF₆平面界面,激波在圆柱绕射后,冲击平面界面,由此研究复杂激波引起的界面变形.平面激波在圆柱绕射后的流场,演化成具有初始入射波、三波点、弯曲反射波、Mach波和Mach反射产生的滑移线等复杂结构.研究复杂结构激波对界面的作用,对认识界面扰动的生成具有较大帮助.绕柱激波冲击后,平面界面仅在两对滑移线内部发生变形.绕柱激波冲击界面后,两对滑移线将界面分成"内界面"和"外界面",界面变形形态同滑移线和界面相交位置相关.反射激波二次冲击下,界面扰动的增长与Jacobs-Sheeley涡量模型较吻合.      

Phase Diagram of a Two-Species Lattice Model with a Linear Instability

We discuss the properties of a one-dimensional lattice model of a driven system with two species of particles in which the mobility of one species depends on the density of the other. This model was introduced by Lahiri and Ramaswamy ( Phys . Rev. Lett ., 79 , 1150 (1997)) in the context of sedimenting colloidal crystals, and its continuum version was shown to exhibit an instability arising from linear gradient couplings. In this paper we review recent progress in understanding the full phase diagram of the model. There are three phases. In the first, the steady state can be determined exactly along a representative locus using the condition of detailed balance. The system shows phase separation of an exceptionally robust sort, termed strong phase separation, which survives at all temperatures. The second phase arises in the threshold case where the first species evolves independently of the second, but the fluctuations of the first influence the evolution of the second, as in the passive scalar problem. The second species then shows phase separation of a delicate sort, in which long-range order coexists with fluctuations which do not damp down in the large-size limit. This fluctuation-dominated phase ordering is associated with power law decays in cluster size distributions and a breakdown of the Porod law. The third phase is one with a uniform overall density, and along a representative locus the steady state is shown to have product measure form. Density fluctuations are transported by two kinematic waves, each involving both species and coupled at the nonlinear level. Their dissipation properties are governed by the symmetries of these couplings, which depend on the overall densities. In the most interesting case, the dissipation of the two modes is characterized by different critical exponents, despite the nonlinear coupling.     

Experimental Investigation of Influence of Interfacial Tension on Convection of Two-Layer Immiscible Liquid

Bdnard-Marangoni convections of two-layer fluids heated from the bottom are investigated experimentally with a particle imagine velocimetry. The flows are visualized from the side, and various velocity fields near the onset of convection, such as three-layer vortex convective patterns, are observed when the depth ratio varies in a wide range. A new classification of the convective patterns is proposed with more detail than in previous studies. The analysis of the results indicates that the interface tension greatly influences the motion intensities of the bottom and top layers. The dimensionless wave number increases with the Bond number when the motion in the top layer is not more intense than that in the bottom layer, which agrees with the theoretical prediction.     

Transition of Bery Phase and Pancharatnam Phase and Phase Change

Berry Phase and time-dependent Pancharatnam phase are investigated for nuclear spin polarization in a liquid by a rotation magnetic field, where two-state mixture effect is exactly included in the geometric phases. We find that when the system of nuclear spin polarization is in the unpolarized state, the transitive phenomena of both Berry phase and Pancharatnam phase are taken place. For the polarized system, in contrast, such a transition is not taken place. It is obvious that the transitions of geometric phase correspond to the phase change of physical system.     

Formulas for ASEP with Two-Sided Bernoulli Initial Condition

For the asymmetric simple exclusion process η _t on the integer lattice with two-sided Bernoulli initial condition, we derive exact formulas for the following quantities: (1) ℙ(η _t (x)=1), the probability that site x is occupied at time t; (2) the correlation function ℙ(η _t (x)=1,η ₀(0)=1); (3) the distribution function for Q _t , the total flux across 0 at time t, and its exponential generating function.     

Gas-Fluid and Fluid-Solid Phase Instability for Restricted Primitive Model

By considering the fluctuation of grand potential Ω around equilibrium with respect to small one-particle density fluctuations δρ_α\vec{r}, the phase instability of restricted primitive model (RPM) of ionic systems is investigated. We use the integral equation theory to calculate the direct correlation functions in the reference hypernetted chainapproximation and obtain the spinodal line of RPM. Our analysis explicitly indicates that the gas-fluid phase instability is induced by k=0 fluctuation mode, while the fluid-solid phase instability is related to k≠0 fluctuation modes. The spinodal line isqualitatively consistent with the result of computer simulations by others.     

Gas-Fluid and Fluid-Solid Phase Instability for Restricted Primitive Model

By considering the fluctuation of grand potential f~ around equilibrium with respect to small one-particle density fluctuations δpα（r→）, the phase instability of restricted primitive model （RPM） of ionic systems is investigated. We use the integral equation theory to calculate the direct correlation functions in the reference hypernetted chain approximation and obtain the spinodai line of RPM. Our anaiysis explicitly indicates that the gas-fluid phase instability is induced by k = 0 fluctuation mode, while the fluid-solid phase instability is related to k ≠ 0 fluctuation modes. The spinodai line is qualitatively consistent with the result of computer simulations by others.     

Phase Effect on Mode Coupling in Kelvin-Helmholtz Instability forTwo-Dimensional Incompressible Fluid

This paper studies the phase effect in mode coupling of Kelvin-Helmholtzinstability in two-dimensional incompressible fluid. It is found that thereis an important growth phenomenon of every mode in the mode couplingprocess. The growth changes periodically with phase difference and in thecondition of our simulation the period is about 0.7π. The periodcharacteristic is apparent in all stage of the mode coupling process,especially in the relatively later stage.     

Detecting the Change of Hawking Temperature with Geometric Phase

We show the possibility to detect Hawking radiation by geometric phase with Dirac particles. If the initial state of the particle is near the ground state, the geometric phase experiences a sudden change with respect to Hawking temperature, which could be employed to detect Hawking radiation. The physical mechanism behind our idea is the population redistribution on the excited state of the particle induced by the event horizon.     

Instability of Solution of Phase Retrieval in Direct Diffraction Phase-Contrast Imaging with Partially Coherent X-Ray Source

The theoretical model of direct diffraction phase-contrast imaging with partially coherent x-ray source is expressed by an operator of multiple integral. It is presented that the integral operator is linear. The problem of its phase retrieval is described by solving an operator equation of multiple integral. It is demonstrated that the solution of the phase retrieval is unstable. The numerical simulation is performed and the result validates that the solution of the phase retrieval is unstable.     

Evidences of the Instability Fixed Points of First-Order Phase Transitions

We study the dynamics of the first-order phase transitions in the two-dimensional Potts model driven by a linearly varying temperature using a finite-time scaling with extended dynamic Monte Carlo renormalization group method. It is found that, for sufficiently large lattice sizes, the flows of apparent exponents of different temperature sweep rates upon renormalization show characteristics that are markedly distinct from those of continuous transitions and are argued to result from the instability fixed points involved and provide a method for estimating the associated instability exponents.     

相变材料模拟金属构件热特性的数值研究

通过理论分析和数值计算论证了用相变材料模拟多种常用金属构件热特性的可行性.利用相变材料模拟了厚度分别为20 mm,30 mm,50 mm和100 mm的金属板材,发现在模拟较厚的金属板材时,相变材料的低导热系数对模拟效果产生了不利影响.在此基础上,利用导热系数增强的相变材料对厚度大于100 mm金属板材进行模拟,取得了较好的模拟效果.并利用相变材料模拟了金属构件轮和管的热特性.