格子Boltzmann方法的质量扩散模型

在《基于格子Ｂｏｌｔｚｍａｎｎ方法的流体力学问题仿真》一文中详细介绍了格子Ｂｏｌｔｚｍａｎｎ方法（ＬＢＭ）的通用模型；模拟了一些典型流体流动现象，证明ＬＢＭ模拟流体流动的简单有效性，适合基于区域分解的分布式算法；首次提出并实现了基于ＬＢＭ的流体力学问题的自动建模算法。现设计一个九点正方形ＬＢＭ的外力模型。设粒子运动方向为ｅｉ＝Ｒｉ（ｃｏｓｉ－１４π，ｓｉｎｉ－１４π），ｉ＝１，２，…，８；ｅ０＝（０，０）。式中Ｒｉ＝｜ｃｏｓｉ－１４π｜＋｜ｓｉｎｉ－１４π｜。流场各节点Ｒ有外力Ｇ（Ｒ），Ｇ（Ｒ）＝（ｇｘ（Ｒ），ｇｙ（Ｒ））＝（ｇｘ（Ｒ），０）＋（０，ｇｙ（Ｒ））＝Ｇｘ（Ｒ）＋Ｇｙ（Ｒ）。则可得到格子Ｂｏｌｔｚｍａｎｎ的外力模型ｆｉ（Ｒ＋ｅｉ，ｔ＋１）＝（１－ω）ｆｉ（Ｒ，ｔ）＋ωｆｅｑｉ（Ｒ，ｔ）＋ｇｉ（Ｒ）ｉ＝０，１，…，８其中：ｆｅｑ０＝４ρ９［１－３２｜ｕ｜２］；ｆｅｑｉ＝ρ９［１＋３（ｅｉ·ｕ）＋９２（ｅｉ·ｕ）２－３２｜ｕ｜２］ｉ＝１，３，５，７；ｆｅｑｉ＝ρ３６［１＋３（ｅｉ·ｕ）＋９２（ｅｉ·ｕ）２－３２｜ｕ｜２］ｉ＝２，４，６，８．ｇｉ（Ｒ）＝［ｓｉｇｎ（＜Ｇｘ（Ｒ）·ｅｉ＞）ｇｘ（Ｒ）＋ｓ?

热声发动机的优化计算设计

把改进的12-Bit格子气模型用于复杂边界的热声发动机的模拟研究,成功模拟了带共振腔的驻波管中热声振荡演化过程。对热声板叠的长度、热声板叠在共振管中的位置以及共振腔的几何大小对热声振荡振幅的影响进行了数值计算。计算结果显示,当共振腔与细管的宽度比为2.2,板叠位置相对于细管长为0.34时,驻波管中热声振荡振幅达到最大。共振腔尺寸的研究,对于热声发动机性能的的优化设计有指导意义。

Boltzmann熵函数的LBM分解及其应用

运用格子气Boltzmann方法 (LBM) ,将Boltzmann熵函数分解成与过程无关的温度熵和体积熵两类成分 ,并对其应用进行了举例 .

Simulation and visualization of the displacement between CO2 and formation fluids at pore-scale levels and its application to the recovery of shale gas

This article reports recent developments and advances in the simulation of the CO2-formation fluid displacement behaviour at the pore scale of subsurface porous media. Roughly, there are three effective visualization approaches to detect and observe the CO2-formation fluid displacement mechanism at the micro-scale, namely, magnetic resonance imaging, X-ray computed tomography and fabricated micromodels, but they are not capable of investigating the dis- placement process at the nano-scale. Though a lab-on-chip approach for the direct visualization of the fluid flow behaviour in nanoscale channels has been developed using an advanced epi-fluorescence microscopy method combined with a nanofluidic chip, it is still a qualitative analysis method. The lattice Boltzmann method （LBM） can simulate the CO2 displacement processes in a two-dimensional or three-dimensional （3D） pore structure, but until now, the CO2 displace- ment mechanisms had not been thoroughly investigated and the 3D pore structure of real rock had not been directly taken into account in the simulation of the CO2 displacement process. The status of research on the applications of CO2 displacement to enhance shale gas recovery is also analyzed in this paper. The coupling of molecular dynamics and LBM in tandem is proposed to simulate the CO2-shale gas displacement process based on the 3D digital model of shale obtained from focused ion beams and scanning electron microscopy.

Rotational Flow in a Narrow Annular Gap Based on Lattice Boltzmann Method

For comprehensive characteristics of flow in a gas bearing,lattice Boltzmann method(LBM)is applied for study of the two-dimensional flow between two eccentric cylinders with the inner one rotating at a high speed.The flow pattern and circumferential pressure distribution are discussed based on critical issues such as eccentricity ranging from 0.2 to 0.9,clearance ratio varying from 0.005 to 0.01 and rotating speed in the range of 3×104—1.8×105 r/min.The analysis and discussion on the circumferential pressure distribution affirmed the quasilinear relation between the extremum pressure and rotating speed.Furthermore,a high eccentricity and small clearance ratio contributes most to the fluctuation of the circumferential pressure distribution.The flow pattern inside the channel exhibits separation vortex under a large eccentricity.The conclusions drawn in this work give rise to prediction of the flow pattern in the gas bearing which is beneficial for evaluating the performance of as well as instructing the design and development.

Numerical Simulation of Two-Dimensional Flow over Three Cylinders by Lattice Boltzmann Method

The numerical simulation using the multiple relaxation time lattice Boltzmann method （MRT-LBM） is carried out for the purpose of investigating the two-dimensional flow around three circular cylinders. Among these three circular cylinders, one of the three cylinders on which a forced in-line vibrating is used to do this research and attempt to find out the effects of the moving cylinder and the other two rigid cylinders on the wake characteristics and vortex formation. As a benchmark problem to discuss the problem of lift coefficient r.m.s for these cylinders with spacing ratios T/ D between other rigid side-by-side cylinders, and the calculation is carried out with two compared cases at Reynolds number of 100, two of the cylinders are rigid and the other one is an in-line vibrated cylinder lying downstream, in addition, forced vibrating amplitude and frequency are A/D = 0.5 and fv= 0.4 （where A is the forced amplitude, D is the cylinder diameter, and fv stands for the vibrating frequency, respectively）. The calculated results not only indicate that the spacing ratios T/D （T is the center-to-center spacing between the two upstream cylinders） have influence on the wake patterns and the formation of vortex shedding, but also analyze the lift coefficient r.m.s for the three cylinders with the spacing ratios S/D （where S is the center-to-center spacing between the center of upstream two side-by-side cylinders and downstream cylinder）.

Inverse Spin Hall Effect in Two-Terminal Device with Rashba Spin-Orbit Coupling

We report a theoretic study on the inverse spin-Hall effect （ISHE） in a two-terminal nano-device that consists of a two-dimensional electron gas （2DEG） with Rashba spin-orbit coupling （RSOC） and two ideal leads. Based on a two-site toy model and Keldysh Green＇s function method, we derive an analytic result of ISHE, which shows clearly that a nonzero transverse charge current stems from the combined effect of the RSOC, the spin bias, and its spin polarization direction in spin space. Our further numerical calculations in a larger system other than two-site lattice model demonstrate that the transverse charge current, dependent on the strength of the RSOC, the Fermi energy of the system, as well as the system size, can exhibit oscillating behavior and even reverse its sign due to Rashba spin precession. These properties may be helpful for eficient detection of the spin current （spin bias） by measuring the transverse charge current in a spin-orbital coupling system.

Graphene as Gas Sensors

The triatomic and tetratomic gas molecule adsorption effects on the electrical conductivity of graphene areinvestigated by the tight-binding model,Green’s function method,and coherent potential approximation.We find thatthe electrical conductivity of graphene sheet is sensitive to the adsorption of these gases.