波纹板表面流体流动特性的数值模拟

利用计算流体动力学CFD商业软件FLUENT,以多相流模型中的VOF模拟为基础,建立了波纹板式的计算模型,考察了液体流速、板面结构、液体物性对液膜流动的影响。模拟结果表明,在一定范围内,随着流速的增加,液膜的厚度和流动时间都减小;波纹板结构直接影响液膜流动,凹槽较浅的波纹板有利于连续液膜的产生,波谷滞留液内发生液体回流形成漩涡;液体的表面张力直接影响连续液膜的产生和断裂,表面张力、黏度、流量共同决定了液膜的厚度和相位差。     

T型微流控芯片中微液滴破裂的数值模拟

利用VOF模型对T型结构微流控芯片中微液滴的三维破裂过程进行了数值模拟,获得了液滴发生破裂和不会破裂两种流型。一定轴向长度的微液滴对应着一个临界毛细数,当主流流体的毛细数大于此临界毛细数时,微液滴发生破裂并分别流向T型结构两侧;否则不会发生破裂,微液滴流向任意一侧。通过多个工况的计算,拟合了临界毛细数与微液滴相对轴向长度的关系,探讨了黏度比对微液滴破裂的影响。发现黏度比越小,微液滴越易发生破裂。     

Inner flow behavior in an oscillating liquid droplet

A numerical simulation was conducted to investigate the inner flow in an oscillating liquid droplet. A 2D model was proposed to describe the interfacial and inner flow of oscillating droplets with shear stress induced by outside air flow. The 2D inner flow field was reconstructed to explore the liquid flow velocity and pressure profile and better understand the oscillating mechanisms. © 2009 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20274     

单桩柱和波浪双向流固耦合的数值模拟

以单桩基支撑结构为对象,建立模拟波浪和单桩柱结构的三维模型,采用k-ε湍流模型和VOF运动界面追踪方法,实现了桩柱和波浪之间的双向流固耦合模拟,得到了波面三维显示图、流固交界面压力分布图和桩柱结构的受力图。还对桩柱上的最大等效应力做了研究,其变化范围是15 704~16 320 Pa,根据Von Mises屈服准则可知,桩柱在这种波浪条件下是稳定的。     

Unstructured finite volume method for water impact on a rigid body

A new method is presented for the water impact simulation, in which the air-water two phase flow is solved using the pressure-based computational fluid dynamics method. Theoretically, the air effects can be taken into account in the water structure interaction. The key point of this method is the air-water interface capture, which is treated as a physical discontinuity and can be captured by a well-designed high order scheme. According to a normalized variable diagram, a high order discrete scheme on unstructured grids is realised, so a numerical method for the free surface flow on a fixed grid can be established. This method is implemented using an in-house code, the General Transport Equation Analyzer, which is an unstructured grid finite volume solver. The method is verified with the wedge water and structure interaction problem.     

电场中导电液滴电场效应的数值模拟

为研究低电导率导电液滴的电场效应,采用开源计算流体力学(CFD)软件OpenFOAM,设计了一种基于漏介质模型(leaky dielectric model)和流体体积(volume of fluid, VOF)法的电流体雾化(electrohydrodynamic atomization, EHDA)求解器,并将数值结果与Taylor的解析值进行了比较.模拟结果预测了液滴的变形方式以及液滴内外的环流模式.研究发现,在外加电场作用下,液滴会发生“扁长型”或“扁圆型”变形,并在内部形成稳定的环流,液滴只会发生变形,而不会发生宏观运动;随着电场强度的增加,液滴的变形越来越大,小变形情况下,模拟值与理论值基本吻合,验证了数值方法的正确性;当液滴的变形量较大时,模拟结果开始偏离理论值,与实验观察结果一致.此外,电导率比值的改变对液滴变形的影响也比较明显,而介电常数比的改变对液滴变形的影响则不太明显.     

NUMERICAL SIMULATION OF EXTREME WAVE GENERATION USING VOF METHOD

Numerical simulations of extreme wave generation are carried out by using the Volume Of Fluid (VOF) method. Extreme waves are generated based on wave focusing in a 2-D numerical model. To validate the capability of the VOF-based model described in this article, the propagation of regular waves is computed and compared with the theoretical results. By adjusting the phases of wave components, extreme waves are formed at given time and given position in the computation. The numerical results are compared with theoretical solutions and experimental data. It is concluded that the present model based on the VOF technique can provide acceptably accurate numerical results to serve practical purposes.     

单液滴撞击薄液膜产生二次雾化过程的数值模拟

应用数值模拟方法研究单液滴撞击薄液膜的动力学行为.在二维轴对称坐标系内,采用VOF方法与网格局部瞬时加密技术相结合,跟踪液滴和液膜与空气间的气液两相界面.结果表明,液滴撞击薄液膜的演化行为主要受液滴初始动能、表面张力以及液体黏性的影响.初始动能越大,则形成的空间液膜最大高度越大,达到稳定状态越晚,飞溅开始时刻越早,飞溅生成的二次液滴数量也越多;在扩展后期及回缩阶段,空间液膜的形成主要受液体黏度影响,增加液体黏度会阻碍空间液膜飞溅;表面张力增大,形成的空间液膜高度减小、厚度增加,同时阻碍二次液滴的生成.     

基于喷墨墨滴沉积铺展的数值模拟与分析

喷墨印刷是一种精确定量沉积技术,能将各种材料沉积在承印材料上成膜或成线。本文借助Fluent软件,利用VOF模型模拟了喷墨墨滴在碰撞铺展阶段的行为特征,数值模拟了墨滴喷射速度、墨滴大小、墨水黏度、墨滴与基板的接触角等因素对碰撞铺展的影响,并结合在电子产品制作中的应用提出了改善这四个影响因素的方法,为喷墨沉积在电子产品制作中的应用提供了一定的理论依据。     

NUMERICAL SIMULATION OF THE ENERGY DISSIPATION CHARACTERISTICS IN STILLING BASIN OF MULTI-HORIZONTAL SUBMERGED JETS

3-D numerical simulation was carried out for the water flow in a stilling basin with multi-horizontal submerged jets by using two different turbulence models, namely, the VOF RNG k - ? and Mixture RNG k - ? turbulence models. The calculated water depth, velocity profile and pressure distribution are in good agreement with the data obtained in experiments. It indicates that the numerical simulation can effectively be used to study the water flow movement and the energy dissipation mechanism. The numerical simulation results show that the turbulent kinetic energy distribution obtained by using the Mixture turbulence model covers a region about 18% larger than that calculated by using the VOF turbulence model, and is in better agreement with the actual situation. Furthermore, the Mixture turbulence model is better than the VOF turbulence model in calculating the air entrainment.