航天器贮箱气液自由界面追踪数值模拟

主要讨论了航天器贮箱在轨道航行时的微重力状态下其液体推进剂在贮箱内的形态分布及控制．文中采用VOF方法，加入了表面张力的效应，追踪气液两相流的自由界面，对液面在微重力条件下的位形变化进行了数值模拟．通过比较不同重力加速度及接触角下的两相流的相图，分析了影响贮箱中液体推进剂位形变化的主要因素及对其有效的控制方法．

分岔管路内的油水相分布特性研究

分岔管路作为一种新型管式分离部件已经在油田上得到了初步应用,与沉降罐和卧式分离器等传统分离设备相比具有分离效率高、体积紧凑、压降损失小等优点。不同入口条件和运行工况下,多相介质在分岔管路内的相分布特性对其分离性能和流动特性有显著的影响,目前这方面的研究还需深入和完善。本研究通过室内实验观察了分岔接头和分支管路内的相分布情况,采用VOF模型中的PLIC方法对分岔管路内的油水相界面进行了数值重构,计算中考虑了混合流速、相含率和流量配比等参数的影响,模拟结果与室内实验符合较好。计算发现,油相在分岔接头和分支管路内发生了明显的拉伸、破碎和变形等现象,在较低的混合流速和相含率情况下油水两相可以得到更为有效的分离,流量配比是影响相分布的最重要的运行参数,这些结论对于指导分岔管路这种新型管式油水分离设备的现场试验具

Influence of Rayleigh-Taylor Instability on Liquid Propellant Reorientation in a Low-Gravity Environment

A computational simulation is conducted to investigate the influence of Rayleigh-Taylor instability on liquid propellant reorientation flow dynamics for the tank of CZ-3A launch vehicle series fuel tanks in a low-gravity environment. The volume-of-fluid (VOF) method is used to simulate the free surface flow of gas-liquid. The process of the liquid propellant reorientation started from initially flat and curved interfaces are numerically studied. These two different initial conditions of the gas-liquid interface result in two modes of liquid flow. It is found that the Rayleigh-Taylor instability can be reduced evidently at the initial gas-liquid interface with a high curve during the process of liquid reorientation in a low-gravity environment.

葛洲坝下游中华鲟产卵河段的流场计算与分析

由于葛洲坝工程的修建,中华鲟的洄游路线被阻断了,使中华鲟产卵场由过去的屏山至木洞800 km江段压缩至现在的葛洲坝下游不足5 km江段。中华鲟也由水产资源演变成一级保护动物。运用水动力学的N-S方程和k-ε紊流数值模型,结合计算水气两相流的方法VOF(volume of fluid),采用控制体积法离散计算区域,对葛洲坝下游中华鲟产卵河段的流场进行了计算。并结合中华鲟的生态特性,分析其产卵繁殖对流场特性的要求,以期在三峡水库下游河道整治中注意保护其产卵场地。

应用气液两相流模型模拟湖泊风生流

采用了基于两相流理论的三维相间界面计算模型模拟湖泊风生流,并采用交错网格的有限体积法求解。该模型应用于昆明市滇池的风生流模拟,实际计算表明该模型算法程序简单,计算结果合理,能较真实的反映湖泊风生流的流态特征。

微重力条件下火箭液氢贮箱重定位过程的数值模拟

采用流体体积法（VOF） 对微重力条件下火箭液氢贮箱的重定位过程进行了三维数值模拟研究。首先结合美国 半人马座液氢贮箱缩比模型的落塔微重力实验，针对无挡板情形，得到了推进剂触底、反弹、碰撞、触顶、顶部清 空和完成重定位六个特征时间，与实验结果符合较好。进一步考虑了环形防晃挡板的影响，得到了重定位时间和邦 德数（Bo）的依赖关系。发现在可靠沉底的前提下，较小的沉底邦德数时完成重定位所需要的总冲量较小，可以节 省推进剂用量。

重定位过程的数值模拟

<结合火箭液氢推进剂贮箱，采用流体体积法(VOF方法)对微重力条件下火箭液氢贮箱中推进剂的重定位过程进行数值模拟研究。针对自由面变形问题建立了完整的数学模型，考虑表面张力效应，研究在不同邦德数(Bo)下自由面变形过程的特点。结合美国半人马座液氢贮箱缩比模型的微重力实验结果，首先考虑无挡板情形，对推进剂重定位过程进行了三维直接数值模拟，得到了推进剂触底、反弹、碰撞、触顶和清空五个特征时间，与美国落塔微重力实验结果符合很好。进一步考虑了环形防晃挡板的影响，完成了相应的数值模拟研究。

分岔管路内的油水相分布特性研究

分岔管路作为一种新型管式分离部件已经在油田上得到了初步应用,与沉降罐和卧式分离器等传统分离设备相比具有分离效率高、体积紧凑、压降损失小等优点。不同入口条件和运行工况下,多相介质在分岔管路内的相分布特性对其分离性能和流动特性有显著的影响,目前这方面的研究还需深入和完善。本研究通过室内实验观察了分岔接头和分支管路内的相分布情况,采用VOF模型中的PLIC方法对分岔管路内的油水相界面进行了数值重构,计算中考虑了混合流速、相含率和流量配比等参数的影响,模拟结果与室内实验符合较好。计算发现,油相在分岔接头和分支管路内发生了明显的拉伸、破碎和变形等现象,在较低的混合流速和相含率情况下油水两相可以得到更为有效的分离,流量配比是影响相分布的最重要的运行参数,这些结论对于指导分岔管路这种新型管式油水分离设备的现场试验具有重要的意义。

Enhancements of the simulation method on the edge effect in resin transfer molding processes

In resin transfer molding processes, small clearances exist between the fiber preform and the mold edges, which result in a preferential resin flow in the edge channel and then disrupt the flow patterns during the mold filling stage. A mathematical model including the effect of cavity thickness on resin flow was developed for flow behavior involving the interface between an edge channel and a porous medium. According to the mathematical analysis of momentum equations in a fully developed rectangular duct and formulations of the equivalent edge permeability, comparing with three-dimensional Navier-Stokes equations, the governing equations were modified in the edge channel. The volume of fluid (VOF) method was applied to track the flow front. A simple case is numerically simulated using the modified governing equations. The effects of edge channel width and cavity thickness on flow front and inlet pressure are analyzed, and the evolution characteristics of simulated results are in agreement with the experimental results. (c) 2007 Elsevier B.V. All rights reserved

Mesoscopic simulation of the impregnating process of unidirectional fibrous preform in resin transfer molding

The resin transfer molding has gained popularity in the preparation of fiber-reinforced polymer-matrix composites because of its high efficiency and low pollution. The non-uniform inter-tow and intra-tow flows are regarded as the reason of void formation in RTM. According to the process characteristics, the axisymmetric model was developed to study the interaction between the flow in the inter-tow space and that in the intra-tow space. The flow behavior inside the fiber tows was formulated using Brinkman's equation, while that in the open space around the fiber tows was formulated by Stokes' equation. The volume of fluid (VOF) method was applied to track the flow front, and the effects of filling velocity, resin viscosity, inter-tow dimension and intra-tow permeability on fluid pressure and flow front were analyzed. The results show that the flow front difference between the inter-tow and intra-tow becomes larger with the decrease of intra-tow permeability, as well as the increase of filling velocity and inter-tow dimension.

Numerical wave flume study on wave motion around submerged plates

Nonlinear interaction between surface waves and a submerged horizontal plate is investigated in the absorbed numerical wave flume developed based on the volume of fluid (VOF) method. The governing equations of the numerical model are the continuity equation and the Reynolds-Averaged Navier-Stokes (RANS) equations with the k-epsilon turbulence equations. Incident waves are generated by an absorbing wave-maker that eliminates the waves reflected from structures. Results are obtained for a range of parameters, with consideration of the condition under which the reflection coefficient becomes maximal and the transmission coefficient minimal. Wave breaking over the plate, vortex shedding downwave, and pulsating flow below the plate are observed. Time-averaged hydrodynamic force reveals a negative drift force. All these characteristics provide a reference for construction of submerged plate breakwaters.