基于CLSVOF方法的三维单个上升气泡运动的数值模拟

运用CLSVOF方法数值模拟了三维单气泡在液体中的上升和变形过程,分别考察了液体的表面张力和浮力对上升气泡变形的影响。计算结果表明:CLSVOF方法能比较精确地跟踪三维单气泡在液体中的上升过程;在相同密度比和粘度比情况下,随着液体表面张力的减小和液体浮力的增大,气泡底部形成的射流使得气泡下缘凹陷变得明显,变形幅度加大,射流穿透气泡的时间提前。     

Numerical simulation of single bubble condensation in subcooled flow using OpenFOAM

The single condensing bubble behavior in subcooled flow has been numerical investigated using the open source code OpenFOAM. A coupled Level Set (LS) and Volume of Fluid (VOF) method (CLSVOF) model with a phase change model for condensation was developed and implemented in the code. The simulated results were firstly compared with the experimental results, they were in great agreements, and thus the simulation model was validated. The validated numerical model was then used to analyze the condensing bubble deformation, bubble lifetime, bubble size history, condensate Nusselt number and other interesting parameters with different variables in subcooled flow. The numerical results indicated that the initial bubble size, subcooling of liquid and system pressure play an important role to influence the condensing bubble behaviors significantly and bubble will be pierced when the subcooling and initial diameter reach a certain value at the later condensing stage. The bubble diameter history and condensate Nusselt number were found in good agreement with the empirical correlation. The drag force coefficient was predicted well by introducing a reduced drag coefficient.     

单液滴撞击平面液膜飞溅过程的CLSVOF模拟

采用CLSVOF(coupled level set and volume of fluid)方法对单液滴撞击平面液膜初期的飞溅过程进行了数值模拟,探讨了撞击速度和液膜厚度对撞击后形成冠状水花形态及扩展直径的影响.结果显示,扩展直径随撞击速度的增大而增大,随液膜厚度的增大而减小,CLSVOF方法可较好地用于液滴撞击过程的数值计算.     

瞬态激振影响下微油滴撞壁行为的数值模拟研究

在油气微量润滑系统工作过程中,有效润滑是保障零件稳定运行的关键。但工作零件的振动会影响油滴的铺展,扰动润滑油膜的形成,从而影响零件的润滑效果。基于CLSVOF方法,建立油滴撞击振动壁面的模型,考察油滴撞击瞬时激振壁面过程中的油液形态演化规律。研究发现：油滴撞击激振壁面后产生飞溅和颈部射流现象;在不同振动频率下,油滴冲击产生二次飞溅的时间均整个周期的1/5附近;壁面振动减小了油滴的最大铺展因子,延长了油滴的铺展时间;在回缩阶段,油滴铺展因子呈现出典型的振荡衰减态势。     

LARGE EDDY SIMLIATION WAVE BREAKING OVER MUDDY SEABED

The Large Eddy Simulation (LES) of the wave breaking over a muddy seabed is carried out with a Coupled Level Set and Volume Of Fluid (CLSVOF) method to capture the interfaces.The effects of the mud on the wave breaking are studied.The existence of a mud layer beneath an otherwise rigid bottom is found to have a similar effect as an increase of the water depth.As compared with the case of a simple rigid bottom,the inception of the wave breaking is evidently delayed and the breaking intensity is much reduced.The dissipation of the wave energy is shown to have very different rates before,during and after the breaking.Before and after the breaking,the mud plays an important role.During the breaking,however,the turbulence as well as the entrainment of the air also dissipate a large amount of energy.     

深层隧道排水系统中井隧水力学特性研究

深层隧道排水系统（深隧）是布置于深层地下的大型排水工程,一般由调蓄隧道、入流竖井、通风设施（排气井）及排水泵站组成,具有调蓄雨洪及控制溢流污染的作用。其中调蓄隧道为避开地铁等城市地下工程往往布置于距离地面30～60 m深处,入流竖井连接地表浅层管网和深层隧道。深隧系统竖井内部的水力学特性复杂,具有单宽流量大、落差高及大量掺气等特点,处理不当将造成较大的破坏。而极端降雨期间,由于未能充分排气而产生的间歇喷涌,也会对设施造成损害。本研究采用物理模型试验和水-气两相流数学模型CLSVOF（CouplingLevel Set and Volume Of Fluid）,研究了不同结构竖井（旋流式竖井和螺旋阶梯式竖井）水力学特性和调蓄隧道中的间歇喷涌问题。根据施工条件设计的两种竖井方案的消能率接近,旋流竖井存在负压及较大震动、排气不畅,而螺旋阶梯式竖井流速较低且流态稳定。在对调蓄隧道中“间歇喷涌”的数值模拟研究中,排气井管径对间歇喷涌的影响十分显著,模拟情景中最剧烈的喷涌会产生5.35倍初始状态下的测压管水头和38.2 m/s的喷涌速度。     

水液滴撞击导流面成膜过程数值模拟

对液滴撞击亲水导流壁面后的液膜形成过程进行了理论分析,用基于CLSVOF方法的数值模型,分析了液滴撞击亲水表面后的铺展特性,研究了不同表面张力系数和液滴直径对液滴撞击亲水表面润湿直径的影响.结果表明,CLSVOF方法可以用于液滴撞击亲水导流壁面的模拟;液滴撞击壁面达到最大润湿直径的时间随着表面张力系数的增大而减小;液滴撞击在亲水壁面上的最大润湿直径随着液滴初始直径的增大而增大,液滴完成一次铺展收缩过程需要的时间也随液滴初始直径的增大而增加;为进一步研究液滴撞击导流壁面成膜对导流壁面的保护作用提供了理论基础.