基于浸没边界—格子Boltzmann方法的带自由液面的水力学问题模拟

为了高效、准确地通过数值方法研究涉及自由液面的流固耦合问题,将单相自由液面格子Boltzmann方法与浸没边界法相结合,提出可计算水流的液面波动及其与刚体相互作用的耦合模型,该耦合模型通过对耦合作用力的迭代,可确保浸没边界的无滑移条件的实现,并可提高耦合模型计算的稳定性和准确性。进而通过该耦合模型模拟和分析了宽顶堰溢流和自由拍门过流两种常见的水力学问题,验证了该模型的可行性和正确性。     

低雷诺数下翼型绕流的格子Boltzmann方法数值模拟

文章采用混合格子Boltzmann方法模拟NACA0012翼型流场分离,该方法是将标准格子Boltzmann方法与非结构化有限体积方程相结合的一种方法。首先,分析不同网格分辨率下的计算精度;然后,分析了在雷诺数等于103的情况下不同攻角下翼型的气动特性;最后,计算了不同雷诺数下攻角为0°时的翼型流场。结果证明,混合格子Boltzmann方法在固体壁面有较高的计算精度,可以准确地评估翼型绕流流场。     

格子Boltzmann方法的竖壁汽液降膜数值研究

对原有的格子Boltzmann伪势模型进行了改进,提出表面张力可调的伪势模型,并基于改进后的伪势两相模型在二维条件下模拟了雷诺数为5、10和20时竖壁降膜的流动,进一步研究了液膜在入口处存在正弦扰动时的流动特性,分析了入口扰动和表面张力作用对液膜稳态波动的影响,总结了液膜稳态波动的规律.结果表明:数值计算得到的流形拓扑及波动特征与实验结论能较好地吻合,表明伪势模型能够较为真实地反映降膜流动的物理过程.     

两相格子Boltzmann方法模拟大密度比下双液滴冲击液膜的流动过程

基于两相格子Boltzmann模型,对大密度比下有一定水平间距的双液滴冲击液膜的流动过程进行了仿真,模拟了不同液滴初始间距和不同雷诺数下液滴冲击液膜的动态过程,重点分析了不同液滴初始间距和雷诺数下产生不同冲击和溅射现象的原因,以及不同参数对冲击和溅射行为的影响.总结了中心位置水花溅射高度随时间的变化规律,并论述了冲击和溅射过程中的内在作用机理.结果表明:在一定范围内,初始间距和雷诺数越大,中心位置水花溅射高度上升越快;随着雷诺数的增大,冲击、碰撞的程度越剧烈,中心位置水花顶端有液滴飞出.     

基于格子Boltzmann方法的饱和土壤渗流与传热数值模拟

本文利用随机多孔介质生成算法重构了与真实土壤外貌相近的多孔介质几何结构。通过引入不可压耦合双分布格子Boltzmann模型（lattice Boltzmann model ,LBM）对孔隙尺度下单相饱和土壤渗流和传热进行了模拟。着重讨论了不同渗流压差、孔隙率、土壤固体颗粒尺寸分布对流动与传热的影响。结果表明：土壤渗流速度与渗流压差呈线性单调递增关系,平均温度随渗流压差增加而增大,但温升速率逐渐减缓;当孔隙率增大时,渗流速度增加,且当孔隙率大于0.58时,对流换热作用迅速增强,土壤温升速率显著加快;对于相同孔隙率,当土壤固相颗粒尺寸较大时,流动出现典型优先流效应;随着土壤固相颗粒尺寸减小,土壤温度变化逐渐趋于平缓,平均温度降低。     

基于格子Boltzmann方法的活塞环润滑和油膜流动研究

使用不可压缩格子玻尔兹曼方法（lattice Boltzmann method, LBM）对活塞环进行润滑和流动计算,采用基于非平衡外推和空间插值的方法来重构活塞环几何形状和界面速度边界,通过Reynolds方程验证了LBM的可行性。在此基础上,建立了3种不同的活塞环桶面轮廓,研究了不同活塞环桶面轮廓对润滑和流动的影响,获得了润滑区域的速度分布和流线图。结果表明,在相同条件下,随着桶面偏移量的增加,峰值压力和承载力增加;在几何收敛区域内,润滑油沿流动方向流速快的流体占比逐渐增加;在活塞环入口位置捕捉到了涡流和反向速度分量的存在,随着桶面偏移的增大,涡流区有扩大的趋势。应用LBM计算活塞环润滑是可行的。     

基于格子Boltzmann方法的微通道受热表面析晶污垢模拟

针对现有的污垢析晶沉积模型不能有效模拟真实污垢生长的问题,建立了一种引入析晶沉积动力学模型的多物理场耦合数值模型。模型基于格子Boltzmann方法和有限差分方法,模拟了微通道非等温热表面上近壁面处的沉积物溶质质量浓度分布和污垢生长过程,研究了流速、壁温和沉积物溶质质量浓度对微通道热表面污垢析晶沉积的影响。结果表明：沉积初始时刻流速和壁温对近壁面沉积物溶质质量浓度分布具有不同程度的影响,随着污垢不断生长,污垢-流体界面处的析晶沉积速率减小;相比于流速,沉积物溶质质量浓度对污垢热阻的影响更为显著。     

流体界面不稳定性耦合作用的格子Boltzmann模拟

使用格子玻尔兹曼方法对二维不混溶、不可压缩流体的Kelvin-Helmholtz(K-H)不稳定性进行数值模拟。以卷起高度H作为参考值,研究了密度比、表面张力、切应力对流体K-H不稳定性内产生Rayleigh-Taylor(R-T)不稳定性的影响。研究结果显示,密度比对两种不稳定性耦合起决定性作用。密度比接近1时,K-H不稳定性中不会产生R-T不稳定性,随着密度比增大,K-H不稳定性中开始产生R-T不稳定性。表面张力系数的增大对流体产生K-H不稳定性及两种不稳定性的耦合的卷起高度变化没有影响,但会对流体向内运动起抑制作用,且卷起流体的厚度明显增加。切应力对两种流体不稳定性的耦合起抑制作用。     

Numerical Simulation of Fluid Flow and Heat Transfer on the Lubricating Surface with Micro‐Groove

The effect of the lubricant flow in the micro‐grooves which resulted from the machining can be expressed in the flow fluid and heat transfer during the mechanical lubrication process. In this paper, a thermal lattice Boltzmann model (LBM), which consists of the heat viscous dissipation term, was proposed to investigate on the lubricants flow and heat transfer in the micro‐grooves. The heat, generated in the lubricating flowing process, was equivalent to a heat source R (x, t) within the fluid and added to the internal energy distribution function. The effect of the heat generated by the fluid on the flow and temperature field can be derived by comparing these two models. The results showed that the fluid temperature rises slower than the mainstream area on account of the vortex motion in the grooves. When the heat source is added to the function, the vortex became larger and the solid boundary was heated by the fluid. Thus, the improved thermal lattice Boltzmann method can accurately simulate the flow of lubricants.     

Improvement of the heat transfer quality by air cooling of three-heated obstacles in a horizontal channel using the lattice Boltzmann method

This study focuses on the cooling of three heated obstacles with different heights mounted on the bottom of the channel wall using different aspects that influence the enhancement of the heat exchange, as is known in the concept of cooling electronic devices. The lattice Boltzmann method associated with multiple relaxation times (LBM-MRT) was adopted to simulate the physical configurations of the studied system. In this context, the D2Q9 and D2Q5 models are applied to describe the fluid flow behavior and conjugate heat transfer, respectively. The evaluation of heat exchange between the cold fluid and three-heated obstacles has been accurately analyzed under the effect of several parameters such as Reynolds number, obstacle spacing, and thermal conductivity ratio. In addition, the setting of two and three fluids flow inlets were also studied. The results are presented in terms of streamlines, isotherms, and local Nusselt curves. The heat transfer increases with increasing solid-fluid thermal conductivity. It is also more pronounced for large Reynolds numbers. Moreover, the heat transfer significantly enhances for the second and third obstacles when obstacle spacing increases. The improvement of the heat transfer is performed by the implementation of several jet flows in the studied system.