数值模拟中低Reynolds数下简单剪切流流过单液滴的稳态流场(英文)

This work presents a numerical investigation on steady internal, external and surface flows of a liquid sphere im-mersed in a simple shear flow at low and intermediate Reynolds numbers. The control volume formulation is adopted to solve the governing equations of two-phase flow in a 3-D spherical coordinate system. Numerical re-sults show that the streamlines for Re=0 are closed Jeffery orbits on the surface of the liquid sphere, and also closed curves outside and inside the liquid sphere. However, the streamlines have intricate and non-closed struc-tures for Re≠0. The flow structure is dependent on the values of Reynolds number and interior-to-exterior vis-cosity ratio.     

Numerical simulations of gas–liquid flow in thermal sorption processes

Thermal storage systems, used, e.g., for domestic heating, must be able to compensate the mismatch between supply and demand. The most efficient techniques for thermal storage are based on sorption storage processes. Usually in sorption, the adsorption process occurs in combination with a solid state adsorbent, whereas absorption takes place in a liquid/gas system. During such sorption processes the flow behavior of the carrier medium is crucial for the efficiency of a falling film absorber. In this work the hydrodynamics of the falling liquid film in two geometrical setups, namely on an inclined plane and over two horizontal parallel tubes, is studied. For the simulation the Eulerian–Eulerian model of the software ANSYS CFX and the interFoam application of the open source software OpenFOAM were used. The numerical results of the two geometries were compared with each other and also with existing data from literature to predict the performance of a sorption storage regarding the specific wetted area and the needed height for gravity driven film absorption.     

示踪剂运移数学模型求解方法研究

随着测试目的的明确和井间示踪的发展,示踪测试解释方法也不断完善和发展。目前,不考虑地质模型进行井间示踪测试解释的方法主要为界标法,结合地质模型进行解释的方法主要有三种:解析方法、数值模拟法、半解析方法。三种方法各有优缺点。从油藏工程的角度,基于流线方法和不稳定渗流场,构建了更为完善的井间示踪产出浓度计算求解半解析方法体系,包括压力场求解、质点追踪方法和流场分解方法等,将三维问题的求解处理为一维问题解的组合形式。     

地下水数值模拟在液体矿采矿设计中的应用

青海钾肥二期工程设计中提出了井群集卤开采方案，为了解决多方案大规模并群计算中庞大的数据处理问题、了解开采生产后区域抽采漏斗的动态变化全过程，以便制定细致、合理的开采方案，引入了地下水数值模拟方法，在计算机上实现了各种方案开采状态的实时模拟。实践证明这一方法是可行的、先进的。     

The dynamic behaviors of diblock copolymer/nanorod mixtures under equilibrium and nonequilibrium conditions

Cylindrical diblock copolymer/anisotropic nanorod composites under equilibrium and nonquilibrium conditions, have been modeled and simulated using dissipative particle dynamics. The aim of our present study is to understand how the anisotropic NRs affect the equilibrium self-assembled structure of diblock copolymers (DBCPs) melts and how the shear flow induces the dynamic behaviors of DBCPs/NRs composites, especially the orientation and distribution of NRs in diblock matrix. We consider two different shear directions categorized with respect to the flow velocity parallel or perpendicular to the orientation of initial structures, which are defined as z-axis shear flow and x-axis shear flow, respectively. Our results show the shear flow not only aligns the orientation of DBCPs template and the dispersed NRs toward the flow direction, but also regulates the orientational and positional order of NRs. The final self-assembly behaviors of DBCPs/NRs nanocomposites is determined by the interplay between shear-induced polymer thinning and NRs dispersion. This work provides us a viable strategy for creating polymer nanocomposites with tunable and enhanced processing properties.     

Effectiveness factor of a catalytic sphere in particle assemblage approached with a cell model

The cell model approach was extended to the catalytic reaction over a spherical catalyst pellet and the effects of several parameters on the effectiveness factor were investigated via numerical simulation. The proposed mathematical model consisted of the partial differential equations for gas reactant flow in the external gas phase around a catalyst sphere, mass transport in the gas phase, and two-dimensional diffusion-reaction in the catalytic sphere. Numerical simulation in the orthogonal boundary fitted reference frame demonstrated the decrease in effectiveness factor of a catalyst sphere due to the external mass transfer resistance and inter-particle hydrodynamic interaction. It was observed that the voidage of the particle assemblage shows more recognized influence than the Peclet and Reynolds numbers of particles and the azimuthal diffusion of reactant inside the particle was negligible. On this basis, a simplified set of cell model equations for catalytic reaction in particle assemblages were proposed. An example of optimizing search indicated the present model may be used to detect the most strong influence on catalytic reaction in particle assemblage over the practical ranges of operating and designing parameters to avoid excessive loss in the effectiveness factor.     

超临界水煤气化过程换热器沉积状况数值模拟研究;

建立了超临界水煤气化换热器在超临界水与煤颗粒体系下的三维瞬态CFD模型,利用IAPWS物性数据库计算超临界水的物性,应用CFX软件模拟研究了竖直放置的超临界水煤气化管壳式换热器的管箱在不同进料条件和换热器结构下的沉积状况并对其结构进行了优化。利用已有的实验结果对模型进行了验证。研究表明,立式换热器管箱垂直进料在减少颗粒沉积方面优于侧边进料和倾斜进料,合适的管箱高度可以减少颗粒的沉积,应尽量减少1mm以上的大颗粒的含量。研究结果对超临界水煤气化过程中使用的换热器的研究设计具有一定的理论意义和工程实用价值。     

Mass and heat transfer from or to a single sphere in simple extensional creeping flow

The first detailed numerical investigation on the mass and heat transfer both outside and inside a solid or liquid sphere immersed in a simple extensional flow for a larger range of Peclet numbers (1–100,000) is presented. By making use of the known Stokes velocity field at small Reynolds numbers, a finite difference method with the control volume formulation is adopted to solve the convection‐diffusion transport equation. Simulation results show that the transport rate, which is represented by Sherwood number, is significantly affected by Peclet number and viscosity ratio. The flow direction, no matter a uniaxial extensional flow or a biaxial extensional flow, has no effect on the total transport rate but affects the concentration distribution a lot. Some comparisons between present simulations and previous studies are made to validate each other and confirm the reliability and applicable scopes of reported correlations. A few new correlations are put forward to predict the transfer rate at finite Peclet numbers for various values of viscosity ratios. © 2011 American Institute of Chemical Engineers AIChE J, 58: 3214–3223, 2012     

气升式环流反应器数值模拟研究进展

介绍了计算流体力学在气升式环流反应器(二相、三相)中的应用,汇总并介绍了气升式环流反应器的气含率和循环液速的二维与三维数值模拟结果,提出今后进一步的研究方向。     

Eulerian-Lagrangian simulation of aeolian sand transport

A numerical investigation of aeolian sand transport is performed with an Eulerian-Lagrangian model. In this model, the gas phase is described by the volume-averaged Navier-Stokes equations of two-phase flow. The particle motion is obtained by solving Newton's second law of motion taking into account the inter-particle collisions, where a soft sphere model is used to describe inter-particle collisions. The dynamic process of aeolian sand transport is simulated. The simulation results show that the variation of mean horizontal velocity of the particles with height can be expressed by a logarithmical function or a power function at h > 0.02 m, and the power function can be described below 0.02 m. The sand mass flux decreases exponentially with height for h > 0.02 m, but there is a deviation from the exponential decay due to the creep grains in the near-bed region. It is also shown that the inter-particle collisions play an important role in sand saltation. Therefore the present numerical model is capable of being applied to the study of windblown sand movement.     

Hydrodynamics of slug flow inside capillaries

Understanding the motion of long gas bubbles (gas slugs) inside capillaries is a challenging problem that is relevant in many processes of chemical and biological interests. It has been proved by many workers that such long gas bubbles can be used successfully in enhancing mass and heat transfer in many chemical and biological processes. In order to quantify and understand this enhancement a light was shed on the hydrodynamics of such a flow pattern. The volume of fluid method implemented in the commercial CFD package, Fluent, is used for this numerical study. Velocity and bubble profile were obtained as functions of capillary number. Computed values of the bubble velocity and diameter were in excellent agreement with published experimental measurements. The detailed velocity field around the bubble was also computed and compared favourably with those experimental results reported in literature.     

Shear-induced nonisothermal crystallization of low-density polyethylene

The effect of melt memory on the shear-induced nonisothermal crystallization of a low-density polyethylene melt is analyzed with a shear DTA instrument. The melt state responsible for the saturation of shear-induced isothermal crystallization was identified previously as the steady state in steady shear flows and the strain applied to the melt was identified as the controlling factor for that saturation. Here it is shown that the same strain that saturates the isothermal crystallization also saturates the shear-induced nonisothermal crystallization. Regardless of the cooling rate, the nonisothermal crystallization, starting from the same sheared melt temperature, saturates at the same strain. The contribution of the melt memory effect to the overall nucleation density is estimated, and it is concluded that the majority of nuclei results from the thermal-induced crystallization.     

NUMERICAL CALCULATIONS OF TUBE BUNDLES EROSION BY TURBULENT PARTICLE-LADEN GAS FLOWS

Erosion of tubes in tube bundles by particles suspended in gas flows is a major problem in the power industry. In this paper, a numerical study has been conducted for the flow of a dilute particle-laden gas moving past two row in-line tubes undergoing erosion. An orthogonal-curvilinear co-ordinate system was used to calculate turbulent flow around the tubes. The prediction of particle trajectories took into account the effect of the turbulence with a stochastic particle dispersion model. The results from this study included the distributions of particle collision frequency and erosion damage of tube surfaces.     

NUMERICAL CALCULATIONS OF TUBE BUNDLES EROSION BY TURBULENT PARTICLE-LADEN GAS FLOWS

Erosion of tubes in tube bundles by particles suspended in gas flows is a major problem in the power industry. In this paper, a numerical study has been conducted for the flow of a dilute particle-laden gas moving past two row in-line tubes undergoing erosion. An orthogonal-curvilinear co-ordinate system was used to calculate turbulent flow around the tubes. The prediction of particle trajectories took into account the effect of the turbulence with a stochastic particle dispersion model. The results from this study included the distributions of particle collision frequency and erosion damage of tube surfaces.     

NUMERICAL PREDICTION OF A RECTANGULAR TURBULENT JET IN A CROSS FLOW

The trajectories and decay of the maximum velocity for turbulent jets in a cross flow were simulated by means of the κ — ? two-equation turbulence model in which differential equations were solved for the kinetic energy of turbulence and for the rate of its dissipation. The solution procedure employed an elliptic finite-difference scheme with the three velocity components and the pressure as the main dependent variables. The essential properties of the jet were discussed in the case of different ratios of the rectangular orifice length to the width H/B, ratios of the jet injected velocity to the main stream velocity R; and different injection angles α. The numerical prediction results were presented in the form of equivalent diameter. Lastly, two correlation equations were obtained and the numerical predictions are shown to agree well with the experimental data.     

液体燃料爆炸抛撒和云雾形成全过程的数值研究

对燃料空气云雾形成过程进行数值模拟。因过程的复杂性分近场与远场两个阶段处理。对近场阶段,利用运动边界处理方法,建立一维气相流动模型和液相运动模型。对远场阶段,采用多相流模型描述云雾膨胀运动过程。将两过程耦合,对抛撒全过程编制程序。数值预测给出了云雾区内的重要物理参数变化,计算的云雾外形变化曲线与实验结果具有较好的一致性。