高浓度颗粒气固两相流动的二阶矩模型的数值模拟

采用动理学方法,用各向异性的M axwell颗粒速度分布函数,建立颗粒相Boltzm ann方程,分别取零次矩、一次矩和二次矩得到颗粒相连续方程、动量方程和二阶矩方程.模拟计算得到上升管内颗粒流场分布和脉动速度分布,与实验结果比较表明:各向异性颗粒动理学能够反映颗粒流动特性,从而能够更全面地认识高颗粒浓度气固两相流动过程.     

等截面喷管中粉气流粉粒初始速度的研究

根据等直径喷管内粉气流运动行为的数学模型以及实验研究，提出用实测初始运动参数确定喷管内粉粒初始速度的方法．并讨论了粉气比、粉粒初速和初始压强等参数之间的关系．     

循环流化床提升管内稠密固液湍流的流体动力学模拟

为揭示循环流化床内稠密固液两相流动特性,对反应器内稠密固液湍流进行了流体动力学模拟.在考虑颗粒碰撞的欧拉-欧拉双流体模型的基础上,通过研究相间拖拽力模型和颗粒碰撞恢复系数的影响,建立了描述循环流化床内稠密固液湍流的流体动力学模型,并利用模型预测了反应器提升管中高浓度颗粒速度、体积分数分布和湍流特性.预测结果与实验结果符合很好,表明理论模型和求解方法有效.     

考虑颗粒对高炉风口回旋区湍流影响的气固两相模型

基于颗粒相欧拉模型,建立了考虑大颗粒对湍流增强作用的颗粒碰撞模型.该模型充分考虑颗粒尾迹对湍流的作用,并把作用结果以源项的形式加入原有模型;在对离散相进行模拟时,还考虑颗粒之间的碰撞作用.最后用该模型对高炉回旋区内的气固两相流动进行了模拟,模拟所得的颗粒平均速度和脉动速度分量与实验结果吻合良好.结果表明,考虑颗粒对湍流增强作用及颗粒之间作用后的新模型预报结果得到了明显改进.     

沙尘天气模拟系统混合段长度计算

应用气固两相流理论计算了沙尘天气模拟系统颗粒自由悬浮速度和混合段长度,利用FLUENT对该系统气固两相流场进行了数值模拟,其中连续相、颗粒相分别采用k-ε湍流模型和离散相模型,相问作用采用随机跟踪模型.结果表明,连续相流场分布规律与理论设计吻合较好,颗粒相浓度场分布可达到试验设计要求.     

LES/FDF simulation of particle dispersion in a gas-particle two phase plane wake flow

A filtered density function (FDF) transport equation was derived for the fluid velocity seen by the particles in gas-particle two-phase flow. An LES/FDF simulation of a two-phase plane wake flow was carried out. The simulation results were compared with both the experimental photograph and the simulation results without using the FDF model, and proved that the LES/FDF model can clearly improve the spatial dispersion of the particle phase.     

含颗粒的幂律流体两相湍流研究

建立了含颗粒的幂律流体两相流动控制方程，首次对泵离心叶轮内含颗粒的幂律流体两相流动进行了计算研究，计算结果表明：从进口到出口，幂律流体的速度减小，压力随半径增大逐渐升高，且压力面上的压力大于吸力面上的压力；吸力面上的颗粒拟温度小于压力面上的颗粒拟温度，且靠近壁面处的大于叶道中的；最后比较了液固两相流与含颗粒的幂律流体的两相流的流动，流体相的紊动能有一定的差别，而且颗粒拟温度也有较大差别。     

自激式除尘脱硫装置流场的数值模拟

利用Fluent软件对SXJ-Ⅱ-L-6T型自激式除尘脱硫装置内的三维二相流场进行数值模拟,气相采用标准k-ε湍流模型,颗粒相采用离散相模型(DPM),选择SIMPLEC算法进行计算。分析了装置内气固二相的速度矢量、压力以及固相颗粒的运动轨迹等参数的分布。分析结果表明,气体流经双层交错式挡板时产生明显压降,同时,双层交错式挡板也延长了气体在塔装置内停留时间,从而实现高效净化气体的目的。     

径向直叶片湿式风机内气固两相流的数值模拟

利用FLUENT软件中离散相模型(DPM)和混合模型对径向直叶片湿式风机内部三维两相流场进行模拟.分析风机内部的气固二相的浓度、体积分数、速度矢量和压力等参数的分布,比较两模型在此次模拟中的优缺点.模拟结果表明,在入口粉尘浓度很低的情况下,固相颗粒的浓度分布与气流流向大致相符.DPM模型颗粒相浓分布和混合模型颗粒相体积分数分布的趋势基本一致.DPM模型在反映浓度局部分布时更加精确,而混合模型在描述整个流场的浓度分布时更加完整.模拟结果对径向直叶片湿式风机气、液、固三相流场和除尘机理的研究有指导意义.     

Two-phase smooth particle hydrodynamics modeling of air-water interface in aerated flows

The large deformations associated with air and water interactions are critical factors that affect the hydrodynamic characteristics of hydraulic structures. As a type of Lagrange meshless particle method, smoothed particle hydrodynamics (SPH) has been shown to have many advantages when modeling the interface flow and tracing the free surface because the particles inherit the velocity, mass, and density properties. Significant theoretical and numerical studies have been performed recently in this area. In the present study, a two-phase SPH framework was developed based on these previous studies and we explored its capacity to capture the main features of large density ratio aerated flows. The cohesive pressure was included only in the momentum equation of the air phase for additional amendments to ensure the stability and accuracy of the two-phase SPH model. Three case studies were performed to test the performance of the two-phase SPH model. A convergence study demonstrated the need to balance the CPU time consumption and the real-time requirements. A dam-break simulation based on pressure variation in the air pocket showed the superior analytical performance of the two-phase model compared with the single-phase model. The results of a hydraulic jump simulation were compared with the theoretical results in order to understand the collision between the solid and liquid using the SPH method more clearly. Thus, the consistency between the simulation and the theoretical and experimental results demonstrated the feasibility and stability of the two-phase SPH framework.     

大涡模拟气固两相三维湍流射流

为了研究三维矩形射流中拟序结构的空间演化和颗粒扩散特征，建立了气固两相矩形射流流场内气体、颗粒两相运动的大涡模拟数学模型，并在此基础上完成了对流动雷诺数等于11 500的气固两相射流的数值模拟.采用亚网格应力模型模拟气相场,并用Lagrangian方法跟踪了颗粒相运动.模拟结果显示了流场流向涡拟序结构随时间发展的演变过程，同时给出了气流相三维拟序结构作用下微细颗粒在整个流场空间中的运动扩散特性.     

基于等分法和迭代算法的磨料射流速度模型

针对前混合磨料射流磨料速度模型中存在的磨料受力考虑不全,无法体现磨料加速度、阻力系数以及雷诺数等关键参数的变化等问题,以固液两相流理论为基础,建立了磨料在高压管路、喷嘴内的速度模型,并基于等分法和迭代算法的数值求解方法,求解了磨料速度模型。计算结果与参考文献的平均百分比误差在5%之内,验证了该算法。同时利用该速度模型得到了磨料在高压管路和喷嘴内的速度、加速度、阻力系数以及雷诺数的变化规律：(1)高压管路内,磨料速度随磨料运动距离的增加逐渐增大,最后无限接近于水的速度;磨料加速度和雷诺数随磨料运动距离的增加逐渐减小,最后会趋于零;而阻力系数则随磨料运动距离的增加逐渐增大。(2)喷嘴收敛段内,磨料速度随磨料运动距离的增加逐渐增大;磨料加速度、阻力系数以及雷诺数随磨料运动距离的增加有一个先减小后增加的过程。(3)喷嘴直线段内,磨料速度随磨料运动距离的增加逐渐增大;磨料的加速度、雷诺数和阻力系数随着磨料运动距离的增加逐渐减小。     

Three-phase flow of submarine gas hydrate pipe transport

In the hydraulic transporting process of cutter-suction mining natural gas hydrate, when the temperature-pressure equilibrium of gas hydrate is broken, gas hydrates dissociate into gas. As a result, solid-liquid two-phase flow(hydrate and water) transforms into gas-solid-liquid three-phase flow(methane, hydrate and water) inside the pipeline. The Euler model and CFD-PBM model were used to simulate gas-solid-liquid three-phase flow. Numerical simulation results show that the gas and solid phase gradually accumulate to the center of the pipe. Flow velocity decreases from center to boundary of the pipe along the radial direction. Comparison of numerical simulation results of two models reveals that the flow state simulated by CFD-PBM model is more uniform than that simulated by Euler model, and the main behavior of the bubble is small bubbles coalescence to large one. Comparison of numerical simulation and experimental investigation shows that the values of flow velocity and gas fraction in CFD-PBM model agree with experimental data better than those in Euler model. The proposed PBM model provides a more accurate and effective way to estimate three-phase flow state of transporting gas hydrate within the submarine pipeline.     

牛顿-幂律流体两相分层紊流的水力特性研究

针对圆管中两相分层紊流流动的水力特性，利用一种新的研究方法——旋转坐标轴法，将圆管流的研究转化为平板流，籍此建立了新的牛顿-幂律流体圆管分层紊流流动模型，得出流动的解析表达式，并通过实验对模型进行了验证。给出了两相分层流以及单相管流的流量积分式，用以验证油气两相分层流是否能相对于石油单相管流实现减阻，为油气混输技术提供理论依据。     

Particle sizing in dense two-phase droplet systems by ultrasonic attenuation and velocity spectra

Size and size distribution of particles in particulate two-phase flow play an important role in a wide variety of industrial areas, while their measurement still remains a hard task till now. Ultrasonic wave as a mechanical vibration contains plenty of information about medium when it passes through. Thus the size distribution could be extracted from the measured ultrasonic attenuation and velocity spectra by means of well established models and data processing techniques. This paper contributes to the extraction of information of droplet size of a two-phase fat emulsion simultaneously from signals of broad-band ultrasonic attenuation and velocity spectra. According to the formulated single particle scattering model, the relationship between particle size distribution and ultrasonic spectrum is established. The sensitivities of ultrasonic spectra to the variation of particle size are illustrated. Distinguishing features for attenuation and velocity spectra are summarized. Demonstration calculations of inversion by optimum regularization factor method are carried out to yield the typical numerical results for discussion. Based on the proposed inversion algorithm and theoretical model, a fat emulsion sample with a volume fraction up to 20% is measured and analyzed. To validate the proposed ultrasonic spectrum particle sizing method, the results are compared to those obtained from optical measurement. Supported by the National Natural Science Foundation of China (Grant Nos. 50706029, 50836003), and Shanghai Nanoscience & Technology Project (Grant No. 0852nm06700)     

齿轮箱飞溅润滑流场分布和搅油力矩损失

齿轮箱飞溅润滑具有齿轮旋转、两相流及流场分布复杂等特点,难以通过理论或实验进行研究;在计算流体动力学方法上,传统的网格法存在动网格处理困难、计算成本高的弊端.针对以上问题,提出运用移动粒子半隐式法(MPS)对齿轮箱飞溅润滑开展仿真分析. 在低转速时,设置不同润滑油型号和温度工况,发现润滑油流场分布情况与试验结果较一致. 在高转速时,设置不同的油温工况,发现相对光滑粒子流体动力学方法(SPH),基于MPS方法数值计算所得的齿轮搅油力矩损失准确度更高,能够准确预测力矩损失变化趋势,但力矩损失预测误差较大,须进一步改进和完善. MPS方法严格保证了流体的不可压缩性,易于追踪捕捉大变形和强非线性化的自由液面,能够较好地分析预测齿轮箱飞溅润滑流场的分布效果.     

气固两相流模型在流场分析中的研究进展

介绍了气固两相流的基本方程、理论模型和研究方法,论述了常用3类模型在流场模拟中的研究进展及应用状况.研究表明,气固两相流模型在工程实践中具有重大的应用价值,并对其研究趋势作出了展望.     

帧差与快速密集光流结合的图像法测流研究

图像法测流技术因其简便、高效、安全等优点得到了普遍的关注,开始应用于国内外水文站。目前主流的图像法测流技术通常采用天然水面模式作为示踪物,利用空域互相关法处理图像获得流场矢量,被称为大尺度粒子图像测速(LSPIV)。但该方法在天然河道流量测量中仍存在着较大不确定性及一致性差等问题,并且由于相关性匹配问题该方法的测量速度很难达到实时性测量要求。本文提出一种基于帧间差分与快速密集光流结合的分组图像法(FD-DIS-G)快速测流方法。首先,利用帧差法计算运动显著性图去捕捉到细微的水面运动来处理低流速下河流运动在视频中表现不明显的问题。其次,使用快速密集光流法(DIS)计算运动显著性图中小块区域之间的密集光流,小块区域和快速密集光流法结合能提高流量测量的精度和时效性。同时,设计了一种新的分组处理奇异值的方法,提高了算法的整体准确性,增强了算法的稳定性。本文将流速仪测量得到的垂线平均流速、平均流速以及断面流量作为比测标准,利用水文站所拍得的天然河道水流视频进行比测实验,实验结果表明,相比于广泛使用的LSPIV测量方法,本文方法在平均流速和断面流量上的精度有明显的提升,垂线平均流速的稳定性有显著的增强,并且实时性好。     

激光干涉成像两相流粒径空间分布测量

为了实现两相流粒径空间分布的测量，研究了激光干涉成像测量技术．激光干涉成像测量技术利用片状脉冲激光束照射粒子场，用数码相机拍摄粒子的散射光干涉图像，并从粒子干涉图像中获取粒子空间位置和粒径分布信息．利用激光粒度仪验证激光干涉成像测量技术的粒径测量精度．实验证明，该技术有较高的测量精度．对水喷雾场的不同片状区域进行测量，从而获得两相流的空间粒径分布．结果显示，所测喷雾场平均粒径由中心区域向边缘区域逐渐变小，大粒子基本集中在中心区域，小粒子基本集中在边缘区域．该方法为研究两相流流场特性提供了一种有效的测量手段．     

三种转子密炼机流体流动和混合特性对比分析

利用有限元法对4WS、4WH 和6WI三种转子密炼机流体的流动和混合特性进行了对比分析。利用UG软件进行三维几何建模,利用Gambit软件进行网格划分,同时采用Bird-Carreau本构模型及Polyflow 软件对三种转子密炼机的流场进行了三维等温数值模拟对比研究。通过对平均速度、轴向速度和剪切速率等进行对比,得到了三者流场的流动规律。同时,利用粒子对数拉伸指数、粒子平均对数拉伸指数、粒子拉伸指数概率、平均混合效率概率和停留时间等参数对三者的分布混合情况进行描述。模拟结果表明,由于6WI转子密炼机本身所具有的特殊变间隙转子结构,更易改变流场的规则流动,其混合性能高于其他两种转子密炼机。