NUMERICAL SIMULATION OF SLOSHING IN RECTANGULAR TANK WITH VOF BASED ON UNSTRUCTURED GRIDS

A new method for sloshing simulation in a sway tank is present, in which the two phase interface is treated as a physical discontinuity, which can be captured by a well-designed high order scheme. Based on Normalized Variable Diagram (NVD), a high order discretization scheme with unstructured grids is realized, together with a numerical method for free surface flow with a fixed grid. This method is implemented in an in-house code General Transport Equation Analyzer (GTEA) which is an unstructured grids finite volume solver. The present method is first validated by available analytical solutions. A simulation for a 2-D rectangular tank at different excitation frequencies of the sway is carried out. A comparison with experimental data in literature and results obtained by commercial software CFX shows that the sloshing load on the monitor points agrees well with the experimental data, with the same grids, and the present method gives better results on the secondary peak. It is shown that the present method can simulate the free surface overturning and breakup phenomena.     

数字微流控芯片半月形驱动电极的设计

为了降低数字微流控芯片的驱动电压,将传统的方形驱动电极结构设计为半月形,并研究了不同参数的半月形驱动电极降低驱动电压的效果。首先,根据介电湿润的基本原理分析了不同驱动电极形状对降低驱动电压的影响。然后,通过流体体积法(VOF)对液滴的运动过程进行建模和数值仿真;根据数值仿真结果对比分析了不同结构参数的半月形驱动电极随驱动时间的运动过程。最后,设计了4种不同结构参数的半月形驱动电极芯片,并对其驱动液滴的效果进行了试验验证。结果表明:研制的4种半月形驱动电极微流控芯片中,电极圆弧直径等于电极长度结构的芯片其驱动电压比其他3种电极结构的芯片的驱动电压至少降低了15.6%,而且可以在16V的驱动电压下使1μL去离子水液滴的运动速度达到1.6cm/s,是设计为半月形驱动电极中的最优设计。实验数据证明了电极圆弧直径等于电极长度的半月形驱动电极结构可有效降低微流控芯片的驱动电压。     

泄洪洞工作闸室及陡坡明渠段体型优化数值模拟

对九甸峡水电站右岸泄洪洞工作闸室,包括圆直段、圆变方段、方洞段、弧形闸门段、渐变段和明渠段流场进行了数值模拟。获得了水面线、压力、空化数、流速等水力要素。成功捕捉到了压力洞出口处的水翅、突扩跌坎处侧空腔和底空腔。计算结果与实测数据符合较好,根据计算结果,提出了能解决原方案负压区严重和明渠陡坡空蚀破坏问题的泄洪洞体型修改方案。     

NUMERICAL SIMULATIONS OF NONLINEAR WAVES OVERTOPPING AN OBSTRUCTION

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转炉顶吹过程渣-金-气三相作用特性

基于VOF界面追踪技术,建立了氧气转炉顶吹过程渣-金-气多相传输行为的数学模型,研究了渣-金-气三相界面行为,给出了渣/金界面特征的演化过程和熔池内流场变化特征,对冲击坑形态进行了具体的描述,并对穿透深度和冲击坑直径进行了定量化的表征。结果表明:由于冲击坑表面波的传播,冲击坑以及渣/金/气界面具有明显的瞬态特征且熔池是振荡的;钢液熔池内涡旋中心位置随着吹炼时间以及渣的运动而变化;低枪位加强了钢液表面的波动,增加了钢液表面的粗糙度,增大了射流与熔池的接触面积,从而有利于射流向熔池的动量传递,促进熔池的搅拌。     

不同多相流模型在航行体出水流场数值模拟中的应用

基于VOF和Mixture两种均相流模型,并结合输运方程类空化模型、k-ε湍流模型和动网格技术,针对圆柱形航行体出水过程进行了数值模拟,获得了无空化、带空泡两种状态下航行体出水过程中的多相流物理景象和表面压力变化历程。根据计算结果分析了VOF模型、Mixture模型在多相流界面捕捉、压力计算等方面的异同,并给出了两种模型的适用范围,在理论研究和工程应用上都具有重要意义。     

基于VOF模型的长输管道水压试验中排空问题的数值仿真分析

长输管道进行水压试验中,排空方式是否合理将严重影响工作效率及试压成本。针对此问题采用VOF模型（Volume of Fluid Model）对管道排气过程进行了数值仿真,并以工程为实例,采取9种排空方式进行计算比较分析。结果表明：管道入口设计成多个均匀分布的入口,以及邻近入口处加1个漏板均可改善排空情况、提高工作效率、降低试压成本。     

Numerical study of stratified oil-water two-phase turbulent flow in a horizontal tube

Stratified oil-water two-phase turbulent flow in a horizontal tube is numerically simulated using a volume of fluid model. A single momentum equation is solved throughout the domain. The RNG k-ε model combined with a near-wall low-Re turbulence model is applied to each phase, and a continuum surface force approximation is adopted for the calculation of surface tension. The simulation is performed in a time-dependent way and the final solution which corresponds to steady-state flow is analyzed. Results of pressure loss, slip ratio, local phase fraction profile and the axial velocity profile are verified by experimental data in literature. Based on the numerical results of extensive calculations, the flow field characteristics are explored and correlations for pressure loss and hold-up are presented.     

基于Fluent的泽尼斯塔混合油滴上升过程模拟

采用泽尼斯法对混合油进行脱酸,可以精炼高酸价油、降低中性油皂化机率、减少皂脚夹油、降低生产成本等。在混合油泽尼斯法脱酸最佳工艺条件下利用Fluent软件,并采用VOF模型对泽尼斯塔内部混合油流动进行CFD数值模拟,得到泽尼斯塔内部流场的混合油相分布、速度矢量分布、绝对速度分布和动压力分布。通过分析模拟结果,可以得到将混合油通过单孔泵入泽尼斯塔时油滴的动力学特性,为泽尼斯塔的优化和油滴分布器的设计提供了新的研究方法和必要的理论依据。另外,通过建立模型进行数值模拟,得到了准确可靠的液—液两相流数据分布。