SECOND-ORDER MOMENT MODEL FOR DENSE TWO-PHASE TURBULENT FLOW OF BINGHAM FLUID WITH PARTICLES

The USM-θ model of Bingham fluid for dense two-phase turbulent flow was developed, which combines the second-order moment model for two-phase turbulence with the particle kinetic theory for the inter-particle collision. In this model, phases interaction and the extra term of Bingham fluid yield stress are taken into account. An algorithm for USM-θ model in dense two-phase flow was proposed, in which the influence of particle volume fraction is accounted for. This model was used to simulate turbulent flow of Bingham fluid single-phase and dense liquid-particle two-phase in pipe. It is shown USM-θ model has better prediction result than the five-equation model, in which the particle-particle collision is modeled by the particle kinetic theory, while the turbulence of both phase is simulated by the two-equation turbulence model. The USM-θ model was then used to simulate the dense two-phase turbulent up flow of Bingham fluid with particles. With the increasing of the yield stress, the velocities of Bingham and particle decrease near the pipe centre. Comparing the two-phase flow of Bingham-particle with that of liquid-particle, it is found the source term of yield stress has significant effect on flow.

REVIEW ON MATHEMATICAL ANALYSIS OF SOME TWO-PHASE FLOW MODELS

The two-phase flow models are commonly used in industrial applications, such as nuclear, power, chemical-process, oil-and-gas, cryogenics, bio-medical, micro-technology and so on. This is a survey paper on the study of compressible nonconservative two-fluid model, drift-flux model and viscous liquid-gas two-phase flow model. We give the research developments of these three two-phase flow models, respectively. In the last part, we give some open problems about the above models.

Transport diffuse interface model for simulation of solid-fluid interaction

For solid-fluid interaction, one of the phase-density equations in diffuse interface models is degenerated to a "0 = 0" equation when the volume fraction of a certain phase takes the value of zero or unity. This is because the conservative variables in phasedensity equations include volume fractions. The degeneracy can be avoided by adding an artificial quantity of another material into the pure phase. However, nonphysical waves,such as shear waves in fluids, are introduced by the artificial treatment. In this paper,a transport diffuse interface model, which is able to treat zero/unity volume fractions, is presented for solid-fluid interaction. In the proposed model, a new formulation for phase densities is derived, which is unrelated to volume fractions. Consequently, the new model is able to handle zero/unity volume fractions, and nonphysical waves caused by artificial volume fractions are prevented. One-dimensional and two-dimensional numerical tests demonstrate that more accurate results can be obtained by the proposed model.

Prediction of mushy zone permeability of Al-4.5wt%Cu alloy during solidification by phase field model and CFD simulation

Liquid permeability of the mushy zone is important for porosity formation during the solidification process. In order to investigate the permeability of the mushy zone, an integrated model was developed by combining the phase field model and computational fluid dynamics (CFD) model. The three-dimensional multigrain dendrite morphology was obtained by using the phase field model. Subsequently, the computer-aided design (CAD) geometry and mesh were generated based on calculated dendrite morphologies. Finally, the permeability of the dendritic mushy zone was obtained by solving the Navier-Stokes and continuity equations in ANSYS Fluent software. As an example, the dendritic mushy zone permeability of Al-4.5wt%Cu alloy and its relationship with the solid fractions were studied in detail. The predicted permeability data can be input to the solidification model on a greater length scale for macro segregation and porosity simulations.

CFD studies of scraper built in SPA clarifying tank based on mixture solid-liquid two-phase flow model

In the industrial process of producing the strong phosphoric acid(SPA),clarification of the solution is essential to the ultimate product.However,the large viscosity of sediment and the induced interface interaction result in difficulties when the SPA is clarified.CFD numerical methodology was applied to simulate internal flow field and performance of the low speed scraper based on Mixture solidliquid two-phase flow model.Sediment deposition was generated by loading solid particles at the bottom of clarifying vessel.The moving mesh and RNG k-εmodel were used to simulate the rotational turbulent flow in clarifying tank.Variables studied,amongst others,were the scraper rotation speed and the mounting height,which could affect the solid suspension height.Features of flow field and solid volume fraction distribution in computational domain were presented and analyzed.The numerical reports of the scraper torque and velocities of inlet and outlet filed were obtained.It seems the torque value of rotatio-nal axis and particle suspending height augment with an increasing rotating speed.Meanwhile,a high revolving speed is good for the deposition discharge.The particle fraction distribution in meridional surface and horizontal surface at fixed rotation speed were analyzed to determine the corresponding optimal installation height.The simulating results reflect the flow field is marginally stirred by the scraper and proper working parameters are obtained,in which case the comprehensive properties of the scraper and the clarifying tank are superior.

FLUID DYNAMICS IN A GAS-STIRRED LADLE——A Separated Flow Model with Stochastical Trajectories

A separated flow model with stochastical trajectories has been developed to describe the fluid flow in a bubble stirred ladle.The bubble dispersion,turbulent characteristics and gas-liquid interactions can be predicted by this mathematical model.The bubble flow as a dispersed phase is treated in a Lagrangian frame of reference and the analysis of the turbulent flow for liquid phase is conducted in a Eulerian field.The interactions between bubbles and liquid phases are considered as a bubble source term in the control equation for a continuous phase. The Monte Carlo sampling method is used to determine the bubble trajectories.The homoge- neous flow model is also taken into consideration so that it can be compared with the sepa- rated flow model.Numerical predictions using a water model of a ladle show that the pre- dicted results of the separated flow model agree satisfactorily with the experimental results, but the prediction of the homogeneous flow model are not in good agreement with the experi- mental results.

A THREE-FLUID MODEL OF THE SAND-DRIVEN FLOW

The sand-driven flow is studied from the continuum viewpoint in this paper. The crux of this work is how to model the stresses of the particle phase properly. By analysing the two-fluid model which usually, works in solving gas-particle two-phase .flow,. we find that this model has many. deficiencies for studying the sand-driven flow,even for the simplest case- the steady, two-dimensional fully-developed flow.Considering this, we have proposed the three-fluid model in which the upward particles and the downward-particles ore regarded as two kinds of fluids respectively.It is shown that the three-fluid model is better than the two-fluid model in reflecting the internal structure of the flow, region and the influence of the boundary situations on the flow. and it is advantageous to find an approximate solution in that the main components of the particle-phase stresses can be explicitly expressed by those variables in the three-fluid model.In the end, the governing equations as well as the boundary. conditions for the three-fluid model are provided with a discussion.

Conditions and Phase Shift of Fluid Resonance in Narrow Gaps of Bottom Mounted Caissons

This paper studies the viscid and inviscid fluid resonance in gaps of bottom mounted caissons onthe basis of the plane wave hypothesis and full wave model, The theoretical analysis and the numerical results demonstrate that the condition for the appearance of fluid resonance in narrow gaps is kh=（2n＋1）π （n=0, 1, 2, 3 ）, rather than kh=nn （n=0, 1, 2, 3, ...）; the transmission peaks in viscid fluid are related to the resonance peaks in the gaps. k and h stand for the wave number and the gap length. The combination of the plane wave hypothesis or the full wave model with the local viscosity model can accurately determine the heights and the locations of the resonance peaks. The upper bound for the appearance of fluid resonance in gaps is 2b/L〈l （2b, grating constant; L, wave length） and the lower bound is h/b〈~ l. The main reason for the phase shift of the resonance peaks is the inductive factors. The number of resonance peaks in the spectrum curve is dependent on the ratio of the gap length to the grating constant. The heights and the positions of the resonance peaks predicted by the present models agree well with the experimental data.

PEMFC船形堵块阴极流场的性能

建立流体体积(VOF)两相流模型,研究船形堵块流道的排水性能。建立不同开孔率的船形堵块流道三维模型,研究船形堵块及开孔率对质子交换膜燃料电池(PEMFC)性能的影响。船形堵块流道峰值净功率密度相较于传统直流道可提升9.4%,相较于同堵塞率下的梯形堵块流道可提高2.9%,具有较好的强化传质作用。通过提高船形堵块流道的开孔率,PEMFC可以获得更好的性能。在相同开孔率下,船形堵块流道的氧气摩尔浓度较直流道和梯形堵块流道分别提高28.6%和14.0%。结果表明,相较于传统直流道,船形堵块流道可降低排水周期和流道内平均水含量,具有更好的排水性能。

非常规储层微纳米孔隙介质中流体相态研究进展

非常规油气储层具有岩石骨架颗粒小、比表面积大、微纳米孔隙发育的特点,流体与孔隙介质间存在着诸多复杂的界面效应问题,影响微纳米孔隙介质中流体的相态变化规律。对于受限域流体,经典油气相态理论方法忽略分子间相互作用及界面效应的影响,预测微纳米孔隙介质中流体相变特征存在偏差。为了更全面地揭示油气在受限空间中的相态特征及其微观作用机理,总结当前微纳米孔隙介质中流体相态研究技术现状,详细阐述微观实验测试、相态理论模型和分子模拟3种主流技术方法,指出3种技术各自的优缺点,并对未来流体相态研究技术提出展望。分析认为:微观实验测试方法可通过研究流体热力学参数的变化来确定流体相变点,由于实验误差、人为误差等原因,需与理论计算相结合;相态理论模型方法可通过改进临界参数场、考虑流体与孔壁界面作用、考虑相间毛管压力修正相平衡判据方程等方法建立纳米孔隙空间相态理论模型,但是由于没有综合考虑界面效应带来的影响且缺乏有力的实验数据支撑,难以推广应用;分子模拟方法能在分子尺度上揭示流体分子的相行为,但现有研究主要围绕小分子展开,并且与流体发生相变时的临界参数结合得较少。后续研究应以多界面效应耦合影响的微纳米孔隙介质中油气流体相变特征为研究对象,以微观实验、理论模型和分子模拟为技术手段,为描述微纳米孔隙介质中流体相态提供合理的实验测试手段和可靠的理论计算模型。

变含水量泥流本构及泥流-桥墩冲刷的流固耦合分析

泥石流是山区主要的地质灾害之一,对山区桥梁破坏严重.在流动过程中,泥石流受到含水量的影响较大,其本构模型会发生变化.本文对泥石流的一种特殊形式——泥流的质量含水量进行分析,将含水量引入泥浆的Herschel-Bulkley模型中,提出质量含水量及剪切速率同时变化下的泥流材料本构模型,并与成都黏土泥浆流变实验对比,验证该模型的正确性.而后基于两相流体的Navier-Stokes方程,将该本构模型应用于三维泥流-桥墩立柱冲击的流固耦合分析中,通过与相关规范及文献冲击压力经验公式计算结果对比,证实了模型的实用性.

欧拉-欧拉双流体模型中颗粒黏性对液固散式流态化的影响

采用无黏性双流体模型、基于颗粒动理学的双流体模型以及Brandani和Zhang简化双流体模型探究了颗粒黏性对液固散式流化特性的影响规律。经与文献中实验数据和Gibilaro公式计算值对比后发现:3种双流体模型均能较好地预测整体固含率,与实验值相对偏差在3%以内,其中无黏性双流体模型和简化双流体模型对固含率预测更符合散式流态化特点;3种双流体模型对时均颗粒轴向速度预测均呈现整体环核结构的固有属性,其中简化双流体模型在较低和较高两组液速工况下预测的相对偏差平均值分别为0.277和1.028;当入口液速突然变化后,收缩过程中简化双流体模型对响应时间预测准确度略高,而膨胀过程中因低浓度区界面不稳定以及膨胀过程中床内颗粒形成的由浓到稀过渡段延长了稳定时间,3种模型预测均与理想过程存在一定偏差,其中液速较低时三者差异不明显,但液速较高时简化双流体模型准确性略高。基于颗粒动理学的双流体模型对动态过程模拟的计算耗时最长。

空间泵驱单相流体回路半物理仿真技术研究

鉴于空间泵驱单相流体回路控制系统研制过程中全物理试验验证涉及的高成本、高风险,以及大气环境下等效模拟空间辐射散热行为存在的挑战,提出一种基于CAN总线的半物理仿真试验平台架构。通过空间热模型代替部分物理实物,结合单相流体回路辐射器地面常压等效验证方法,实现空间泵驱单相流体回路控制系统动态特性的在线快速、可信验证。试验结果表明:在3种工况下,系统控温精度普遍可以达到±0.5℃;常规PID控制策略与神经元PID控制策略的控温性能差别不大;短期瞬态高热流冲击对主回路控温点温度的影响不超过1℃。研究可为空间泵驱单相流体回路控制系统开发与验证提供一种新的技术途径。

阳春沟区块页岩气超临界CO_(2)增能压裂研究与应用

目的目前,超临界CO_(2)压裂应用前景广阔,为更好地指导现场应用,亟需明确超临界CO_(2)压裂的起裂压力和裂缝扩展规律。方法考虑压裂过程温度变化对CO_(2)物性的影响以及岩石中的热应力作用,建立热流固耦合超临界CO_(2)压裂模型。探究了水平应力差、天然裂缝逼近角以及CO_(2)注入温度对裂缝起裂的影响。结果在阳春沟Y井开展的现场试验表明:与水力压裂相比,超临界CO_(2)压裂可以明显降低裂缝起裂压力,即使在高水平应力差下,仍可以获得复杂的裂缝形态;天然裂缝逼近角增大,起裂压力随之增大,裂缝复杂程度增加;CO_(2)注入温度与地层温差越大,热应力作用越明显,裂缝形态越复杂。结论现场应用显示注入前置超临界CO_(2)可以有效降低起裂压力,有利于提高后续水力压裂的缝内净压力,增强储层改造效果。

过滤双流体模型的水平管道内稠油输送数值模拟

针对介观尺度下蜡晶颗粒聚团在管壁形成宏观尺度下石蜡层的现象,采用过滤双流体模型研究水平管道输送伴有固态沥青质的稠油的液固两相流流动和传热特性.对比均匀结构曳力模型和亚格子曳力模型的模拟结果,获得了颗粒相时均体积分数、颗粒相压力和过滤传热系数的修正系数等参数分布规律.同时分析了壁面温度对稠油温度分布和传热的影响.结果表明:与均匀模型Gidaspow model相比,过滤模型能够揭示蜡晶颗粒非均匀流动结构对液固两相流的变化规律.Filtered modelⅡ的结果更加接近于试验结果,Filtered modelⅡ的结果随着蜡晶颗粒体积分数的增加而减小.当蜡晶颗粒相体积分数增加到12%时,加入壁面修正的亚格子模型的误差仅为4.1%.而ZAMBRANO等人模拟结果与试验压降的误差为12.9%.亚格子尺度模型能够详细地再现沥青质颗粒聚团的介观尺度流动行为,为稠油输送过程中的蜡晶聚集以及流动过程的预测提供了新的方法.

基于可压缩两相流模型的注射成型填充模拟

基于现有的超算平台及有限体积法计算程序,开发了一种用于注射成型的三维数值模拟计算模型。该模型数值方法基于可压缩两相流,考虑了熔体和气体的密度变化,即将熔体和空气这两种不同性质的流体,采用同一套控制方程进行计算。采用有限体积法进行离散,通过压力隐式算子分割算法(PISO)求解压力-速度耦合方程组,结合流体体积(VOF)法进行界面追踪。首先模拟了带圆柱嵌件的平板型腔填充过程,采用六面体为主导的方法划分了三种不同网格系统,定量比较三种网格下的速度基本一致,从而验证了网格的收敛性。考虑到计算效率,选取M2(网格数为106876个)网格系统,模拟了温度、剪切速率和压力在不同截面上的分布。结果表明,在填充时间(t)为0.6,0.8,1.4 s时刻下熔体流体前沿的界面追踪模拟与实验吻合;在更复杂的不均匀厚度凹槽平板熔体填充模拟过程中,塑料熔体注入型腔时,会先在薄壁凹槽内流动,随后流进厚壁区域。在t为0.125,0.25,0.375 s时刻下的流动前沿会产生形状像喷泉的流锋,这种流动现象可以通过三维模型预测,与商业软件仿真结果呈现基本一致。随着填充速率的增大,注射压力数值与Moldflow结果更接近。

基于气−水两相流的注热CO_(2)增产CH_(4)数值模拟研究

注CO_(2)增产煤层气技术(CO_(2)−ECBM)可以降低温室气体排放,具有清洁能源生产和环境保护的功能。为研究气−水两相流条件下,在含水煤层中注CO_(2)增产CH_(4)的排采规律以及不同初始含水饱和度、不同CO_(2)注入条件对CH_(4)产量、CO_(2)储存和储层渗透率的影响,构建了竞争吸附、温度变化、煤体变形以及水运移的流−固−热耦合模型,通过与现场数据、已有试验以及现有模型的数值解结果,对比证明了模型有较高的准确性并对模型的优势做出具体阐述,随后利用COMSOL开展了CO_(2)−ECBM数值模拟。结果表明:注CO_(2)可以提升CH_(4)产气速率和产气量,这表明了注CO_(2)增产的可行性。随着CO_(2)持续注入,储层CH_(4)浓度降低,CO_(2)浓度升高,注气井附近温度升高,生产井附近温度降低且从注气井到生产井的温度缓慢下降;注气抽采期间,水相相对渗透率逐渐减小,气相相对渗透率逐渐增大。由于有效应力、基质收缩/膨胀共同作用,储层渗透率呈现“降低—升高—降低”的趋势;煤层初始含水饱和度越大,CH_(4)产量越低,渗透率下降幅度越小。累计CH_(4)产量最大下降15.19%,忽略煤层中水的影响会高估CH_(4)产量,在进行数值模拟时要考虑煤层水的影响;CO_(2)注入温度与注入压力越大,CH_(4)产量越大,渗透率下降幅度越大。累计CH_(4)产量分别增加13.27%、39.77%,渗透率分别下降20.4%、46.14%,提高CO_(2)注入温度和注入压力有利于提高CH_(4)产量。

Fluid Flow Behavior of Liquid in Cylindrical Vessels Stirred by One or Two Air Jets

Based on the two-phase model (Eulerian-Eulerian model), the three dimensional fluid flow in water and that liquid steel systems stirred by one or two multiple gas jets are simulated. In the Eulerian-Eulerian two-phase model, the gas and the liquid phase are considered to be two different continuous fluids interacting with each other through the finite inter-phase areas. The exchange between the phases is represented by source terms in conversation equations. Turbulence is assumed to be a property of the liquid phase. A new turbulence modification - model is introduced to consider the bubbles movement contribution to and . The dispersion of phases due to turbulence is represented by introducing a diffusion term in mass conservation equation. The mathematical simulation agrees well with the experiment results. The study results indicate that the distance of two nozzles has big effect on fluid flow behavior in the vessel. Using two gas injection nozzles at the half radii of one diameter of the bottom generates a much better mixing than with one nozzle under the condition of the same total gas flow rate.

Fluid-induced high-temperature metasomatism at Rundv?gshetta in the Lützow-Holm Complex, East Antarctica: Implications for the role of brine during granulite formation

We report new petrological, phase equilibria modeling, and fluid inclusion data for pelitic and mafic granulites from Rundv?gshetta in the highest-grade region of the Neoproterozoic Lützow-Holm Complex(LHC),East Antarctica, and provide unequivocal evidence for fluid-rock interaction and high-temperature metasomatism in the presence of brine fluid. The studied locality is composed dominantly of well-foliated pelitic granulite(K-feldspar+quartz+sillimanite+garnet+ilmenite) with foliation-parallel bands and/or layers of mafic granulite(plagioclase+orthopyroxene+garnet+ilmenite+quartz+biotite). The boundary between the two lithologies is defined by thin(about 1 -20 cm in thick) garnet-rich layers with a common mineral assemblage of garnet+plagioclase+quartz+ilmenite+biotite ? orthopyroxene. Systematic increase of grossular and decrease of pyrope contents in garnet as well as decreasing Mg/(Fe+Mg) ratio of biotite from the pelitic granulite to garnet-rich rock and mafic granulite suggest that the garnet-rich layer was formed by metasomatic interaction between the two granulite lithologies. Phase equilibria modeling in the system NCKFMASHTO demonstrates that the metasomatism took place at 850 -860℃, which is slightly lower than the peak metamorphism of this region, and the modal abundance of garnet is the highest along the metapeliteemetabasite boundary(up to 40%), which is consistent with the field and thin section observations. The occurrence of brine(7.0 -10.9 wt.% Na Cleqfor ice melting or 25.1 -25.5 wt.% NaC leqfor hydrohalite melting) fluid inclusions as a primary phase trapped within plagioclase in the garnet-rich layer and the occurrence of Cl-rich biotite(Cl = 0.22 -0.60 wt.%) in the metasomatic rock compared to that in pelitic(0.15 -0.24 wt.%) and mafic(0.06-0.13 wt.%) granulites suggest infiltration of brine fluid could have given rise to the high-temperature metasomatism. The fluid might have been derived from external sources possibly related to the formation of major suture zones formed during the Gondwana amalgamation.

水下近自由面爆炸过程中的多相流运动特性研究

水下近自由面爆炸现象涉及到爆轰气体产物、水以及空气等多种流体之间的相互作用过程,同时还伴随有明显的汽液两相之间的相变转换。为了理解和掌握近水面爆炸过程中的多流体非线性耦合特性,引入基于相变转换的多相可压缩流体计算模型进行分析。采用一维激波管问题对计算模型的精确性和收敛性进行测试验证,在此基础上利用二维轴对称模型模拟近水面爆炸过程,获得冲击波传播、空化产生与溃灭、爆炸气泡运动等过程。爆炸气泡运动的计算结果与试验结果具有一致性。对于由水下爆炸引起的近自由面空化现象,数值模拟清晰展示了空化域的产生、发展及其溃灭的完整过程。空化域由开始的单连通域演化为涡环形态,并向外扩展直至完全溃灭。将蒸汽体积分数0.5‰作为空化域的识别判据时,计算获得的空化域的演化过程与试验结果较为一致。数值模拟结果还进一步揭示了空化域内部的一些重要的物理特性,本文的研究结果能够为水面舰艇结构的抗爆抗冲击防护研究提供技术支撑。