共查询到19条相似文献,搜索用时 62 毫秒
1.
2.
基于介观模型的多组分伪势格子Boltzmann方法,模拟了倾斜壁面浸润性梯度驱动液滴的运动过程,研究了壁面浸润性梯度、壁面倾斜角度对液滴运动过程的影响.结果表明,对于一定倾斜角度的壁面,当壁面上浸润性梯度足够大时,液滴能够克服重力的作用实现“爬坡”;液滴在运动过程中,其前进及后退接触角与当地静态接触角间存在差值;增大壁面浸润性梯度时,液滴能够获得更快的加速,并且前进及后退接触角与当地静态接触角之间的差值也随之增大;增大壁面倾斜角度时,液滴的运动受到阻碍,前进及后退接触角与当地静态接触角的差值小幅减小. 相似文献
3.
采用改进的格子Boltzmann方法,对梯度润湿性表面上液滴的定向迁移及合并行为进行了数值模拟,该模型在精度和稳定性上都有很大改善,同时,研究了梯度润湿性表面上液滴定向迁移和合并的动力学特性,并对液滴尺寸及润湿梯度对液滴动力学特性的影响规律进行了分析。数值结果表明,液滴在梯度润湿性表面运动时会发生形变,且动态接触角逐渐减小。润湿梯度对液滴定向迁移行为有显著影响,润湿梯度越大,液滴左右侧接触线位移越大,润湿长度增加越快。但是液滴尺寸对接触线位移影响较小。润湿梯度对液桥宽度基本无影响,但对液滴初始合并时间有显著影响。 相似文献
4.
利用格子Boltzmann方法对气泡在液体中的运动规律及相互作用的气液两相流问题进行了研究;采用了基于自由能模型且适用于大密度比多相流问题的Z-S-C模型,计算模拟了处于不可压缩流体中的气泡在浮力作用下的运动特性;通过算例验证了Z-S-C模型的可行性;研究了不同放置位置两气泡的运动形态及其相互作用情况,分别分析了沿y方向同轴放置的两气泡间距变化对合并过程和沿x方向并列放置的两气泡的间距变化对气泡相互作用的影响。结果表明:两气泡的初始间距在一定范围内时,初始间距对上升过程中气泡间的相互作用具有重要影响;当初始间距超过一定量值时,上升过程中两气泡相互独立,不存在相互作用。 相似文献
5.
并列圆柱绕流的格子Boltzmann数值模拟 总被引:1,自引:0,他引:1
采用非均匀不可压格子Boltzmann模型对低雷诺数下并列圆柱绕流进行了数值模拟,给出了数值计算结果,分析了间距g对圆柱尾流及升力、阻力的影响,并在此基础上得到了4种尾迹模式.此外,研究了流场的初始扰动对流动分岔现象的影响,发现在适当的扰动下可以很快得到同步同相的尾流.对Re=160和200下圆柱的升、阻力进行了对比,结果表明升力和阻力受间距g的影响大于雷诺数. 相似文献
6.
采用格子Boltzmann方法对较大Rayleigh数范围下的二维Rayleigh-Benard对流进行了模拟研究.引入能量分布函数,利用该能量分布函数与粒子速度分布函数耦合来求解一个热流场,能量分布函数与粒子速度分布函数和Boltzmann方程构成了一个新的双分布格子Boltzmann模型.在考虑密度随温度变化的情况下,进行数值模拟,得到了Rayleigh-Benard对流速度、温度随时间的变化规律、系统的流线和等温线分布及平均Nusselt数与Rayleigh数的之间的关系,与相关文献数据进行了对比,模拟结果非常吻合,证明了改进的双分布格子Boltzmann模型的有效性. 相似文献
7.
8.
格子Boltzmann方法可以有效地模拟水动力学问题,边界处理方法的选择对于可靠的模拟计算至关重要.本文基于多松弛时间格子Boltzmann模型开展了不同边界条件下,周期对称性结构和不规则结构中流体流动模拟,阐述了不同边界条件的精度和适用范围. 此外,引入一种混合式边界处理方法来模拟多孔介质惯性流, 结果表明:对于周期性对称结构流动模拟,体力格式边界条件和压力边界处理方法是等效的,两者都能精确地捕捉流体流动特点; 而对于非周期性不规则结构,两种边界处理方法并不等价,体力格式边界条件只适用于周期性结构;由于广义化周期性边界条件忽略了垂直主流方向上流体与固体格点的碰撞作用,同样不适合处理不规则模型;体力-压力混合式边界格式能够用来模拟周期性或非周期性结构流体流动,在模拟多孔介质流体惯性流时,比压力边界条件有更大的应用优势,可以获得更大的雷诺数且能保证计算的准确性. 相似文献
9.
用格子Boltzmann方法模拟Belousov-Zhabotinsky反应中的靶型波 总被引:2,自引:0,他引:2
构造了用于Belosov-Zhabotinsky反应的格子Boltzmann模型。通过对使用多组分的分布函数满足的格子Boltzmann方程,进行多重尺度Knudsen数展开,得到了模型的平衡态分布函数的各向同性解。作为算例,给出随机初始条件下反应区域内的靶型波的模拟结果,再现了Belousov-Zhabotinsky反应的经典结果。 相似文献
10.
11.
Xiaoding Cheng Yunlong Zhu Chiyuan Wang Shuailong Li 《International Journal of Computational Fluid Dynamics》2017,31(10):450-462
Three-dimensional computations on the basis of the index-function lattice Boltzmann method are performed to simulate the process of multiple droplets impinging and coalescing into a line pattern on a solid substrate. The employed calculation model is validated by theoretical calculated values and experimental data from the literature. The influences of the equilibrium contact angle, droplet spacing and impinging velocity on the droplets impingement and coalescence behaviours are investigated. Numerical results demonstrate the width of the formed line depends significantly on the equilibrium contact angle and droplet spacing. The droplet spacing plays a significant role in controlling the coalescence moment of multiple droplets. The resolution of the printed pattern can be slightly increased with increase in impinging velocity. 相似文献
12.
对格子Boltzmann方法提出了一种新的曲面边界条件处理方法。在笛卡尔坐标系中,这种处理方法是现有的格子Boltzmann方法有关边界条件处理与浸入式边界条件的混合,它采用内插值方法计算靠近物理边界的网格点速度,使其保证最低精度为二阶,然后利用格子Boltzmann方法中的边界条件技术得到相应的分布函数。由理论推导和数值计算表明,本文提出的方法比其他方法更稳定且具有二阶精度。 相似文献
13.
The computational method presented here can be used to study the effect of volume fraction and particle deformation on the rheology and microstructure of deformable fibers suspended in Newtonian fluid. In this method, the flow is computed on a fixed regular ‘lattice’ using the lattice Boltzmann method, where each solid particle is mapped onto a Lagrangian frame moving continuously through the domain. Instead of the standard bounce-back method, an external boundary force is used to impose the no-slip boundary condition at the fluid–solid interface for stationary or moving boundaries. The motion and orientation of the fiber are obtained from Newtonian dynamics equations. Although the external boundary force method is general, in this application it is used in conjunction with a flexible fiber model, which calculates the flexible fiber deformation by the real material properties. The methodology is validated by comparing with experimental and theoretical results. 相似文献
14.
Generalized Lattice Boltzmann equation (GLBE) was used for computation of turbulent channel flow for which large eddy simulation (LES) was employed as a turbulence model. The subgrid‐scale turbulence effects were simulated through a shear‐improved Smagorinsky model (SISM), which is capable of predicting turbulent near wall region accurately without any wall function. Computations were done for a relatively coarse grid with shear Reynolds number of 180 in a parallelized code. Good numerical stability was observed for this computational framework. The results of mean velocity distribution across the channel showed good correspondence with direct numerical simulation (DNS) data. Negligible discrepancies were observed between the present computations and those reported from DNS for the computed turbulent statistics. Three‐dimensional instantaneous vorticity contours showed complex vortical structures that appeared in such flow geometries. It was concluded that such a framework is capable of predicting accurate results for turbulent channel flow without adding significant complications and the computational cost to the standard Smagorinsky model. As this modeling was entirely local in space it was therefore adapted for parallelization. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
15.
Based on the lattice Boltzmann (LB) approach, a novel hybrid method has been proposed for getting insight into the microscale characteristics of the multicomponent flow of nanofluid. In this method, the whole computational domain is divided into two regions in which different-sized meshes are involved for simulation (fine mesh and coarse mesh). The multicomponent LB method is adopted in the fine mesh region, and the single-component LB approach is applied to the coarse mesh region where the nanofluid is treated as a mixed single-component fluid. The conservation principles of mass, momentum and energy are used to derive a hybrid scheme across the different scaled regions. Numerical simulation is carried out for the Couette flow and convective heat transfer in a parallel plate channel to validate the hybrid method. The computational results indicate that by means of the present method, not only the microscopic characteristics of the nanofluid flow can be simulated, but also the computational efficiency can be remarkably improved compared with the pure multicomponent LB method. 相似文献
16.
17.
The phase-change problem is solved by the migration-collision scheme of lattice Boltzmann method. After formula derivation, we find that this method can give a rigorous numerical value for the phase-change temperature, which is of crucial importance. One-dimensional solidification in half-space and two-dimensional solidification in a corner are simulated. The phase change temperature and the liquid-solid interface are both obtained, and the results conform to the analytical solution. 相似文献
18.
In this paper, a large eddy simulation based on the lattice Boltzmann framework is carried out to simulate the heat transfer in a turbulent channel flow, in which the temperature can be regarded as a passive scalar. A double multiple relaxation time (DMRT) thermal lattice Boltzmann model is employed. While applying DMRT, a multiple relaxation time D3Q19 model is used to simulate the flow field, and a multiple relaxation time D3Q7 model is used to simulate the temperature field. The dynamic subgrid stress model, in which the turbulent eddy viscosity and the turbulent Prandtl number are dynamically computed, is integrated to describe the subgrid effect. Not only the strain rate but also the temperature gradient is calculated locally by the non-equilibrium moments. The Reynolds number based on the shear velocity and channel half height is 180. The molecular Prandtl numbers are set to be 0.025 and 0.71. Statistical quantities, such as the average velocity, average temperature, Reynolds stress, root mean square (RMS) velocity fluctuations, RMS temperature and turbulent heat flux are obtained and compared with the available data. The results demonstrate great reliability of DMRT–LES in studying turbulence. 相似文献
19.
The effect of rough surface topography on heat and momentum transfer is studied by direct numerical simulations of turbulent heat transfer over uniformly heated three-dimensional irregular rough surfaces, where the effective slope and skewness values are systematically varied while maintaining a fixed root-mean-square roughness. The friction Reynolds number is fixed at 450, and the temperature is treated as a passive scalar with a Prandtl number of unity. Both the skin friction coefficient and Stanton number are enhanced by the wall roughness. However, the Reynolds analogy factor for the rough surface is lower than that for the smooth surface. The semi-analytical expression for the Reynolds analogy factor suggests that the Reynolds analogy factor is related to the skin friction coefficient and the difference between the temperature and velocity roughness functions, and the Reynolds analogy factor for the present rough surfaces is found to be predicted solely based on the equivalent sand-grain roughness. This suggests that the relationship between the Reynolds analogy factor and the equivalent sand-grain roughness is not affected by the effective slope and skewness values. Analysis of the heat and momentum transfer mechanisms based on the spatial- and time-averaged equations suggests that two factors decrease the Reynolds analogy factor. One is the increased effective Prandtl number within the rough surface in which the momentum diffusivity due to the combined effects of turbulence and dispersion is larger than the corresponding thermal diffusivity. The other is the significant increase in the pressure drag force term above the mean roughness height. 相似文献