密相液固两相湍流流动研究

在ＩＰＳＡＲ算法基础上推导了适用于考虑液度变化影响的密相液固两相湍流流动数值计算的ＤＩＰＳＡＲ算法，并采用低雷诺数模型，对竖直上升管中密相液固两相湍流分别采用ＩＰＳＡＲ算法和ＤＩＰＳＡＲ算法进行了数值计算，计算值与实测值较符合，计算结果的比较表明ＤＩＰＳＡＲ算法能更有效地预测密相液固两相湍流流动     

旋转直管内气固或液固两相流动浓度分布

本文针对旋转直管内气固或液固两相流动，建立了经过适当简经处理的颗粒无量纲运动方程，得到了稳定状态下直管内颗粒的浓度分布公式，从而为气固两相流风机或液固两相流泵的颗粒浓度分布研究打下了基础。     

旋转、弯曲、扩散流道中液固两相流场的数值模拟及其分析

本文简要介绍了旋转、弯曲、扩散流道中,液—固两相流数值计算结果,进而从理论上分析了泵叶轮压力面遭受磨损和输送两相流时扬程降低的原因。     

旋转,弯曲,扩散流道中流固两相流场的数值模拟及其分析

本文简要介绍了旋转,弯曲,扩散流道中,液－固两相流流数值计算结果,进而从理论上分析了泵叶轮压力面遭受磨损和输送两相流时扬程度降低的原因。     

层状两相流动的基本方程式

本文将两相流动的雷诺方程沿深度方向进行平均,出求了平均后的运动方程、连续方程和能量方程式,在适当的物理假定下,简化得到可适用于考虑固-液流动及气-液流动两种情况下的两相层状流动基本方程.     

气液两相流动与固壁相互作用耦合求解的研究

气液两相流动与固壁相互作用的研究是液滴撞击壁面运动研究的重要基础.以结合了VOF和Level Set两种方法优点的用于气液相界面追踪的复合Level Set-VOF方法和利用唯象分析方法建立的能够反映接触角滞后性及壁面性质对润湿过程影响的壁面润湿模型为基础,提出了气液两相流动与固壁相互作用耦合求解流程,给出了气液两相流动与固壁相互作用耦合求解过程中接触线速度的计算方法及边界条件的确定方法.通过与已有实验结果的对比,对提出的气液两相流动与固壁相互作用耦合求解方法的有效性进行了验证.     

高浓度固液两相流压力测量

本文介绍了确定水煤浆流动阻力的试验装置,应用膜片或传压器的传感器,可用来测定高浓度固液两相流压力。     

90°弯管内气固两相湍流流动的数值研究

利用两相湍流KET模型对90°弯管内气固两相湍流流动进行了数值模拟,得到了弯管内两相流动的一些规律,并提出用颗粒动理学压力来定性表征弯管内磨损严重部位,为管道抗磨损设计提供了一定的理论依据。     

两相流PIV粒子图像处理方法的研究

本文在单相PIV技术的基础上研究了两相流动PIV图像处理方法，采用摸板匹配法和灰度加权标定法对两相粒子进行了识别、区分和标定，采用灰度互相关法对区分后的单相粒子图像进行了处理，应用基于以上方法编制的Windows应用软件，首先对由美国Minnesota大学复杂流动实验室提供的两相流动粒子图片进行了处理，通过对比分析可见，应用本文所采用的方法能对两相粒子进行有效的识别和区分，然后以搅拌槽内液固两相流场为例对此方法进行了应用。     

两相正激波松弛流的数值研究

对气、固两相正激波松弛流动进行了数值研究,方程中考虑了压力梯度及非匀速运动引起的附加质量力。给出了完整的计算方法,对三种不同固相容积比、不同固相颗粒直径和不同马赫数分别进行了数值计算,所得计算结果给出了气、固两相的速度、温度、压力、密度、固相容积比及熵值沿流向分布情况。文章对气、固两相参数在松弛区中的变化规律进行了讨论。     

Simultaneous velocimetry/accelerometry measurements in a turbulent two-phase pipe flow

A two-color digital particle image velocimetry and accelerometry (DPIV and DPIA) measurement technique is described that records the velocity and acceleration fields of both the solid and liquid phases simultaneously. Measurements were taken at turbulent conditions of a vertical pipe flow using glass spheres as the solid phase and fluorescent particles to indicate fluid phase motion. Nd-YAG pulse lasers acted as illumination sources and images were recorded by two monochrome CCD cameras. The two-color aspect of the technique was realized by placing optical filters in front of the cameras to discriminate between the phases. Cross-correlations and auto-correlations were applied to determine velocity and acceleration fields of the two phases. Results showing some of the capabilities of the technique as applied to a two-phase pipe flow experiment are provided. For the condition studied, it was found that there was turbulence suppression due to the solid phase and that the statistics associated with the acceleration probability distribution were different for the solid and fluid phases.     

高浓度固-液两相流紊流的动理学模型

采用分子动理学方法,基于固-液两相流液相分子或颗粒相颗粒的Boltzmann方程,对Boltzmann方程分别取零矩和一次矩,则得到高浓度固-液两相流紊流的连续方程和动量方程,再和较成熟的低浓度两相流连续方程和动量方程比较,取低浓度两相流控制方程中较成熟合理的有关项和高浓度时由动理学方法推导出的颗粒间碰撞项,则得到高浓度固-液两相流紊流的最终控制方程:连续方程和动量方程.     

Numerical calculations of erosion in an abrupt pipe contraction of different contraction ratios

Erosion predictions in a pipe with abrupt contraction of different contraction ratios for the special case of two‐phase (liquid and solid) turbulent flow with low particle concentration are presented. A mathematical model based on the time‐averaged governing equations of 2‐D axi‐symmetric turbulent flow is used for the calculations of the fluid velocity field (continuous phase). The particle‐tracking model of the solid particles is based on the solution of the governing equation of each particle motion taking into consideration the effect of particle rebound behaviour. Models of erosion were used to predict the erosion rate in mg/g. The effect of Reynolds number and flow direction with respect to the gravity was investigated for three contraction geometries considering water flow in a carbon steel pipe. The results show that the influence of the contraction ratio on local erosion is very significant. However, this influence becomes insignificant when the average erosion rates over the sudden contraction area are considered. The results also indicate the significant influence of inlet velocity variations. The influence of buoyancy is significant for the cases of low velocity of the continuous flow. A threshold velocity below which erosion may be neglected was indicated. Copyright © 2004 John Wiley & Sons, Ltd.     

RESEARCH ON METHOD TO CALCULATE VELOCITIES OF SOLID PHASE AND LIQUID PHASE IN DEBRIS FLOW

Velocities of solid phase and liquid phase in debris flow are one key problem to research on impact and abrasion mechanism of banks and control structures under action of debris flow. Debris flow was simplified as two-phase liquid composed of solid phase with the same diameter particles and liquid phase with the same mechanical features. Assume debris flow was one-dimension two-phase liquid moving to one direction, then general equations of velocities of solid phase and liquid phase were founded in two-phase theory. Methods to calculate average pressures, volume forces and surface forces of debris flow control volume were established. Specially, surface forces were ascertained using Bingham's rheology equation of liquid phase and Bagnold's testing results about interaction between particles of solid phase. Proportional coefficient of velocities between liquid phase and solid phase was put forward, meanwhile, divergent coefficient between theoretical velocity and real velocity of solid phase was provided too. To state succinctly before, method to calculate velocities of solid phase and liquid phase was obtained through solution to general equations. The method is suitable for both viscous debris flow and thin debris flow. Additionally, velocities every phase can be identified through analyzing deposits in-situ after occurring of debris flow. It is obvious from engineering case the result in the method is consistent to that in real-time field observation.     

Drag models for simulating gas–solid flow in the turbulent fluidization of FCC particles

This paper examines the suitability of various drag models for predicting the hydrodynamics of the turbulent fluidization of FCC particles on the Fluent V6.2 platform. The drag models included those of Syamlal–O’Brien, Gidaspow, modified Syamlal–O’Brien, and McKeen. Comparison between experimental data and simulated results showed that the Syamlal–O’Brien, Gidaspow, and modified Syamlal–O’Brien drag models highly overestimated gas–solid momentum exchange and could not predict the formation of dense phase in the fluidized bed, while the McKeen drag model could not capture the dilute characteristics due to underestimation of drag force. The standard Gidaspow drag model was then modified by adopting the effective particle cluster diameter to account for particle clusters, which was, however, proved inapplicable for FCC particle turbulent fluidization. A four-zone drag model (dense phase, sub-dense phase, sub-dilute phase and dilute phase) was finally proposed to calculate the gas–solid exchange coefficient in the turbulent fluidization of FCC particles, and was validated by satisfactory agreement between prediction and experiment.     

稠密气固两相湍流流动的实验和数值模拟

基于气固两相流动模型计算循环流化床内稠密气固两相流湍流动,颗粒动理学方法模拟颗粒相湍动能,ＳＧＳ模型模拟气相湍流,采用γ－射线密度计和非等速取样管测量局部颗粒浓度和流率,利用ＦＦＴ方法计算颗粒浓度功率谱密度。模拟计算得到上升管内气相和固相速度和浓度分布等。同时数值模拟与Ｔｓｕｊｉ等和Ｋｎｏｗｌｔｏｎ等试验结果进行了比较,结果表明数值模拟计算与实验结果相吻合。     

稠密气固两相流各向异性颗粒相矩方法

基于气体分子动力学和颗粒动理学方法,考虑颗粒速度脉动各向异性,建立颗粒相二阶矩模型.应用初等输运理论,对三阶关联项进行模化和封闭.考虑颗粒与壁面之间的能量传递和交换,建立颗粒相边界条件模型.采用Koch等计算方法模拟气固脉动速度关联矩.考虑气体-颗粒间相互作用,建立稠密气体-颗粒流动模型.数值模拟提升管内气固两相流动特性,模拟结果表明提升管内颗粒相湍流脉动具有明显的各向异性.预测颗粒速度、浓度和颗粒脉动速度二阶矩与Tartan等实测结果相吻合.模拟结果表明轴向颗粒速度脉动强度约为平均颗粒相脉动强度的1.5倍,轴向颗粒脉动能大约是径向颗粒脉动能3.0倍.     

Counter-current three-phase fluidization in a turbulent contact absorber: A CFD simulation

A computational fluid dynamics study of three-phase counter-current fluidization occurring in a turbulent contact absorber was performed. A two-dimensional, transient Eulerian multi-fluid model was used, in which the dispersed solid phase was modeled employing a kinetic theory of granular flow. The grid independence of the model, the effect of wall boundary conditions, the choice of granular temperature model, the effects of order of discretization scheme and drag models were studied for a base case setting. The results of simulations were validated against experimental results obtained from the literature. Once the model settings were finalized, simulations were performed for different gas and liquid velocities to predict the hydrodynamics of the absorber. Computed bed expansion and pressure drop were compared with experimental data. Good agreement between the two was found for low velocities of gas and liquid.     

Effect of a liquid dispersed phase on the wall flow structure in static mixer

The effect of a liquid dispersed on the wall flow structure in static mixer is analyzed by using an electrochemical method. Both laminar and turbulent flows have been investigated. The axial wall velocity gradient and turbulent intensity have been studied along the static mixer in both flow regimes and for different dispersed phase concentrations. The spectral analysis of the wall velocity gradient fluctuations was analyzed in the turbulent regime. For volume fraction higher than 5%, the effect of the dispersed liquid phase is very important for all the studied parameters. The turbulence associated to the dispersed phase leads to an increase of the energy dissipation in the static mixer and also to a modification of energy dissipation mechanism.     

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

The USM-θmodel 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-θmodel 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-θmodel 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-θmodel 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.