致密多孔介质中气体渗流的格子Boltzmann模拟

为了能用格子Boltzmann方法来正确地刻画致密多孔介质中微尺度流动问题,对单通道模型进行推广,并将其应用于孔隙群里气体渗流的数值模拟.通过对部分具有代表性的多孔介质中的实际流动问题进行模拟,研究渗透率与平均压力和Knudsen数之间的相互关系.基于理论分析及相关文献中的试验结果,验证模拟结果,为用格子Boltzmann方法深入研究气体渗流问题奠定基础.     

基于格子Boltzmann方法的超声速非平衡流模拟

基于D1Q4可压缩格子Boltzmann模型,按照流通矢量分裂方法的思路,采用坐标旋转技术构造求解三维带化学反应Navier-Stokes方程对流通量求解器.结合有限体积法求解三维化学非平衡流Navier-Stokes方程,采用时间算子分裂算法解决化学反应刚性问题,数值模拟超声速化学非平衡流的三个经典算例.数值结果表明:在高马赫数下,采用D1Q4可压缩格子Boltzmann模型构造的三维对流通量求解器数值模拟中没有出现非物理解,同时在超声速化学非平衡流场中正确分辨激波、燃烧波等物理现象,精度和分辨率均较高,验证了本文构造的三维对流通量求解器的可靠性,拓宽了D1Q4可压缩格子Boltzmann模型的应用范围,为计算超声速化学非平衡流提供一种新方法.     

微通道中气体流动的格子Boltzmann数值模拟

采用可压缩格子Boltzmann模型及非平衡外推边界条件,数值模拟微通道中的气体在滑移区域(Kn≤0.1)内的流动,计算结果包括出口速度剖面、通道中心压力分布以及质量流率等,与理论结果及其他实验结果符合得很好.还模拟了180°弯曲通道中的气体流动.结果表明,滑移速度的存在抑制了边界层的分离,因此在弯曲处不存在漩涡.计算结果还表明,弯道的存在显著影响了气体的质量流率.     

耦合不可压流场输运方程的格子Boltzmann方法研究

基于格子Boltzmann方法,提出了求解耦合不可压缩流场输运方程的一种改进数值方法. 该方法使用格子Boltzmann方法求解流场方程,并根据流场格子模型的密度分布函数构建了输运方程的二阶离散格式. 通过二维平板通道流场输运系统验证了该方法的有效性.数值结果表明,该方法可以有效地减少计算过程中出现的非物理耗散, 并克服了传统模型所需巨大存储量的缺点.     

跨流域高超声速绕流环境Boltzmann模型方程统一算法研究

如何准确可靠地模拟从外层空间高稀薄流到近地面连续流的航天器高超声速绕流环境与复杂流动变化机理是流体物理的前沿基础科学问题. 基于对Boltzmann方程碰撞积分的物理分析与可计算建模, 确立了可描述自由分子流到连续流区各流域不同马赫数复杂流动输运现象统一的Boltzmann模型速度分布函数方程, 发展了适于高、低不同马赫数绕流问题的离散速度坐标法和直接求解分子速度分布函数演化更新的气体动理论数值格式, 建立了模拟复杂飞行器跨流域高超声速飞行热环境绕流问题的气体动理论统一算法. 对稀薄流到连续流不同Knudsen数0.002 ≤Kn_∞ ≤1.618、不同马赫数下可重复使用卫星体再入过程(110–70 km)中高超声速绕流问题进行算法验证分析, 计算结果与典型文献的Monte Carlo直接模拟值及相关理论分析符合得较好. 研究揭示了飞行器跨流域不同高度高超声速复杂流动机理、绕流现象与气动力/热变化规律, 提出了一个通过数值求解介观Boltzmann模型方程, 可靠模拟高稀薄自由分子流到连续流跨流域高超声速气动力/热绕流特性统一算法.     

格子Boltzmann方法对Rayleigh-Benard流的模拟与非线性分析

本文利用格子Boltzmann方法对不同Ra下的Rayleigh-Benard自然对流进行了数值模拟,得到的Nu与前人的结果一致。数值结果表明,Ra=2000时,格子Boltzmann方法得到了三个静态分岔解,其中一个为非稳定解;在Ra=5×10~5时格子Boltzmann方法得到了类似于周期的振荡解。本文采用插值格子Boltzmann方法,在Ra=2000,取不同插值节点进行计算时,得到了一种非稳态解。     

模拟可压缩流体的格子Boltzmann模型

在简单声速可调模型的基础上,通过在演化方程中引入一个吸引势来降低有效声速从而提高Mach数,建立高Mach数下的可压缩格子Boltzmann模型．利用Chapman-Enskog渐进展开法推导相应的宏观流体力学方程．与粘滞流体的Navier-Stokes方程比较表明,该模型有降低声速的功能．模拟结果表明,该模型可将Mach数提高到3以上,且与理论值符合．该模型的建立为用格子气模拟可压缩流体打开广阔前景． 关键词：     

低温均匀相变的格子Boltzmann方法模拟

文中基于气液两相接触时的传质机理和两相格子Boltzmann理论模型,提出相界面的密度数处于气液相密度数之间,对低温液滴相变进行了模拟研究。在低温状态下,对单个液滴进行了均匀蒸发现象模拟,分析了不同过热度对蒸发速率的影响,并模拟运动液滴的相变。结果表明,所采用的格子Boltzmann方法能够有效分析模拟低温介质的相变。     

用格子Boltzmann模型模拟可压缩完全气体流动

采用一种新的格子Boltzmann模型模拟超音速流动。在这种模型中,粒子的速度不受限制,可以取得很广。而平衡分布函数的支集却相对集中,使模型得以简化。粒子速度的这种自适应特性允许流体以较高的马赫数流动。通过引入粒子的势能使得该模型适用于具有任意比热比的完全气体。利用Chapman-Enskog方法,从BGK型Boltzmann方程推导出Navier-Stokes方程。在六边形网格上模拟了马赫数为3的前台阶绕流,得到了合理的结果。     

椭圆柱体在牛顿流体中运动的格子Boltzmann方法模拟

用格子Boltzmann方法建立了椭圆柱体的二维动力学模型，利用所建立的模型，数值模拟了 牛顿流体中不同形状的椭圆柱体在相同初始条件下的运动和同一椭圆柱体在不同初始条件下 的运动，并通过比较相同条件下圆柱体的运动，讨论了椭圆柱体二维运动的特征，得到了一 些有意义的结果. 关键词： 格子Boltzmann方法 椭圆柱体 牛顿流体     

Lattice Green's Function for the Diamond Lattice

An expression for the Green's function (GF) of diamond lattice is evaluated analytically and numerically for a single impurity interacting with the first nearest-neighboring host atoms. The density of states (DOS), phase shift and scattering cross-section are expressed in terms of complete elliptic integrals of the first kind.     

Lattice Green's Function for the Body-Centered Cubic Lattice

An expression for the Green's function (GF) of Body-Centered Cubic (BCC) lattice is evaluated analytically and numerically for a single impurity lattice. The density of states (DOS), phase shift, and scattering cross section are expressed in terms of complete elliptic integrals of the first kind.     

Lattice calculations

In this contribution we describe how an exact chiral symmetry can be realized on the lattice. A practical realization of a lattice Dirac operator that leads to a chiral invariant lattice action is discussed and a simulation with this operator is presented that aims at testing the phenomenon of spontaneous chiral symmetry breaking in QCD.Received: 30 September 2002, Published online: 22 October 2003PACS: 11.15.Ha Lattice gauge theory - 12.38.Gc Lattice QCD calculations     

Lattice QCD

Possibilities that are provided by a lattice regularization of QCD for studying nonperturbative properties of QCD are discussed. A review of some recent results obtained from computer calculations in lattice QCD is given. In particular, the results for the QCD vacuum structure, the hadron mass spectrum, and the strong coupling constant are considered.     

Diffusion Lattice Boltzmann Scheme on a Orthorhombic Lattice

We present a diffusion lattice Boltzmann (DLB) scheme which is derived from first principles. As opposed to the traditional lattice BGK schemes the DLB is valid for orthorhombic lattices and it has two eigenvalues of the collision operator. It is shown that the diffusion coefficient depends only on one eigenvalue of the collision operator. Hence, the DLB scheme can be optimized with means of the additional eigenvalue of the collision operator and with different lattice spacing along the principal axes. The properties of the DLB scheme concerning consistency, stability, and accuracy are studied with eigenmode analysis. This analysis shows that the DLB scheme is consistent with diffusion for a wide range of diffusion coefficients, it has unconditional stability, and that it has third-order accuracy. Furthermore, it is shown that accuracy is improved by setting the additional eigenvalue to zero and by densifying the lattice spacing along the direction of the density gradient.     

Lattice Green's Function for the Face Centered Cubic Lattice

An expression for the Green's function (GF) of face centered cubic (FCC) lattice is evaluated analytically and numerically for a single impurity problem. The density of states (DOS), phase shift and scattering cross section are expressed in terms of complete elliptic integrals of the first kind.     

Lattice Boltzmann Solid Particles in a Lattice Boltzmann Fluid

We define a lattice Boltzmann model of solid, deformable suspensions immersed in a fluid itself described in terms of the lattice Boltzmann method. We discuss the rules governing the internal dynamics of the solid object as well as the rules specifying the interaction between solid and fluid particle. We perform a numerical drag experiment to validate the model. Finally we consider the case of a population of flexible chains in suspension in a shear stress flow and study the influence on the velocity profile.     

Lattice Green's Function for the Face Centered Cubic Lattice

An expression for the Green's function (GF) of face centered cubic (FCC) lattice is evaluated analytically and numerically for a single impurity problem. The density of states (DOS), phase shift and scattering cross section are expressed in terms of complete elliptic integrals of the first kind.