三维熔体前沿界面的Level Set追踪

给出三维Level Set方程,采用五阶加权本质无振荡格式进行空间离散,通过算例验证了该算法的正确性及追踪三维运动界面的准确性。进而将Level Set算法和同位网格有限体积法进行耦合,模拟了注塑成型充填阶段的三维流动过程,准确追踪到了不同时刻熔体前沿界面,预测并分析了流动过程中不同时刻的压力、速度等重要流动特征。数值结果表明,该方法可追踪三维熔体前沿界面,预测充填过程中的重要流动特征。     

冷却塔轴流风机三维流场数值模拟与影响因素分析

本文运用CFD软件对轴流风机进行了三维数值模拟,采用SIMPLEC算法和Realizable k-ε湍流模型,求解三维时均N-S方程,计算出轴流风机的内部流场,获得了轴流风机内部许多重要的流动细节、速度和压力分布规律及其性能参数,并对影响轴流风机性能的主要参数(如进口速度、转速和叶片安装角度等)进行了对比模拟,可获得各个参数对轴流风机性能的影响。     

中比转数离心泵内部流场的三维数值模拟

基于全三维不可压缩雷诺时均方程和RNGk-ε湍流模型,采用压力-速度隐式修正SIMPLEC算法,应用FLUENT软件中提供的多重参考系模型(MRF),对具有扭曲叶片的中比转数离心泵内三维不可压缩湍流流动进行数值模拟,探讨泵流道内的压力及速度分布规律,揭示泵内的回流、高速、高压流动现象.结果表明:扭曲形叶片汽蚀性能较好,但靠近隔舌流道内的回流、叶片流道内的局部高速和高压流场会影响离心泵效率,对隔舌和叶轮叶片结构进行优化是提高中比转数离心泵效率的途径之一.     

注塑模充填过程动态模拟

本文基于注塑模型腔内充填机理和流体力学基本方程，视聚合物熔体在型腔中的流动为平行板中的流动，在浇注系统中的流动为等效圆柱管内的流动，在此假定的基础上进行合理简化，建立了三维薄壁型腔的基于非弹性、非牛顿流体在非等温下的Ｈｅｌｅ－Ｓｈａｗ流动的数学模型及浇注系统的数学模型，并采用混合有限元／有限差分数值方法耦合求解压力方程和能量方程，采用控制体积法自动跟踪熔体前峰面，从而实现充填过程的动态模拟。模拟结     

基于CFD的离心泵流场数值模拟

为了研究离心泵内部流场的流动规律,验证CFD数值模拟的可靠性,基于CFD技术,应用雷诺时均N-S方程与标准k-ε湍流模型对不同工况下高速离心泵内部的三维湍流流动进行了数值模拟,并对其内部的流动状态进行了分析得到了离心泵内部流场的压力分布规律,外特性试验和CFD模拟下的泵性能曲线。结果表明:出口的压力值是最大的,泵的整体压力随着出口流量不断增大而减小。在相同工况下下,离心泵进口到出口的压力逐渐增大。通过CFD模拟所得结果与实验结果基本吻合,本文中建立的CFD数值模拟的求解模型能可靠的预测出Q5H26型离心泵的水力性能。     

塑料熔体在注塑模中的三维流动模拟

建立了非等温条件下黏性、不可压缩、非牛顿流体流动的控制方程.为了避免同时求解耦合的压力场、速度场,通过修改传统方法的变分方程导出了关于压力场的拟Poisson方程,用迭代法独立求解连续性方程、动量方程,并进行速度场-黏度迭代求出最终的压力场、温度场.这种方法可以减少内存,提高数值方法的稳定性,避免了Hele-Shaw模型中容易引起争议的“中面”概念,并能模拟中面方法不能模拟的一些物理现象.算例表明数值结果与实验结果吻合较好,这种方法可以成功地预测注射成型流动过程中的重要特征.     

基于P1/PO四面体宏元的三维注塑充填速度场压力场有限元数值模拟

计算效率和解的稳定性是影响三维注塑充填有限元数值模拟的关键因素.针对黏性不可压缩聚合物熔体三维充填过程的速度场和压力场,以提高计算机求解速度为出发点,分析了采用P1/P0四面体单元(速度线性,压力常数)得到的有限元方程的解不收敛的原因,提出一种采用P1/P0四面体宏元离散空间域的求解方案,从而降低了求解的自由度数量,提高了计算速度.通过模拟"圆管中定黏度流体的稳态流动"考察了该求解方案的模拟精度,通过模拟"圆管中定黏度流体的瞬态充填"比较了采用P1/P0四面体宏元和P2/P1四面体单元(二次速度,线性压力)的计算时间.最终将该方案应用到三维注塑充填的数值模拟中.     

混流式风机内部流体力学行为研究

基于k-ε湍流模型和三维时均N-S方程,进行了混流式风机的全流道三维定常湍流计算,得到了风机内部压力分布和速度分布等许多重要的流动现象。结果表明,风机的全通道CFD分析能够较为准确地预测出风机内部流场结构。     

压力旋流式喷嘴喷淋液膜区换热过程的数值模拟

利用Fluent软件对压力旋流式喷嘴的内外流场进行了数值模拟，以等效的二维网格模型模拟圆周对称的三维流动，多相流和湍流模型分别采用VOF和雷诺应力模型。在两种条件下，对喷嘴流场进行模拟：①气相为空气，不发生相间热质传递；②气相为饱和水蒸气，发生相间热质传递。相变模型采取Fluent中内嵌的Lee模型。将数值模拟结果同实验结果进行对比，并以数值模拟的数据对喷嘴内外流场展开分析。模拟结果显示，由于液相在喷嘴旋流室内的螺旋运动，导致喷嘴内部形成“空气芯”，液相速度在喷嘴旋流室与收缩段的连接处变化剧烈；另外，发生相间热质传递条件下，流场的压力要整体稍低且速度场的速度最大值更大；液膜的传热系数沿液膜流动方向不断减小；因气相冷凝使得液膜厚度更大，液膜破碎长度也因蒸气冷凝而变得更长。     

料仓中粉体流动数学模型分析

对料仓中粉体流动进行模拟可以获得粉体流动的压力、流动速度、相组分和相浓度分布。模拟料仓中粉体流动有3种数学模型:有限元素模型、离散元素模型和混合模型,每种模型各自适用于不同的流动区域,混合模型集合了前2种模型的优点,是模拟料仓中粉体流动的最先进模型。     

基于两相流流型的平行流冷凝器整体仿真模型与实验验证

引言平行流冷凝器作为一种新颖的换热器加之其不同于传统翅片管换热器的结构,因此其传热流动性能尚处研究之中。尤其是平行流冷凝器制冷剂侧微通道两相流机制及其转变不同于常规的管子,以往关于平行流冷凝器整体仿真模型的研究中,微通道两相流数值模拟大都采用传统大管径模型或者修正     

环形狭缝通道内气液两相环状流流动特性

建立了环形狭缝通道内气液两相环状流的理论模型 ,该模型计及环状流气芯流动的可压缩性、气液两相间的相滑移、气相对液滴的夹带作用等因素 .考察了两相流质量流量和干度对压降、液滴速度相对变化和狭缝喉部气芯通流面积的影响 .用建立的理论模型对空气 -水两相环状流通过环形狭缝的两相压降进行预测 ,预测值和试验值吻合良好     

Flow‐Field Designs of Bipolar Plates in PEM Fuel Cells: Theory and Applications

A generalized model developed by Wang was modified for flow field designs of the most common layout configurations with U‐type arrangement, including single serpentine, multiple serpentine, straight parallel, and interdigitated configurations. A direct and quantitative relationship was established among flow distribution, pressure drop, configurations, structures, and flow conditions. The model was used for a direct, systematic, and quantitative comparison of flow distributions and pressure drops among the most common layout configurations of interest. The straight parallel configuration had the lowest pressure drops but suffered the most possibility of the uneven flow distribution across the channels. The single serpentine had the best flow distribution but had the highest pressure drops. The flow distribution and the pressure drop in the multiple serpentine was between the straight parallel and the single serpentine. Finally, we suggested basic criteria of the flow field designs of bipolar plates for the industrial applications. This provides a practical guideline to evaluate how far a fuel cell is from design operating conditions, and measures how to improve flow distribution and pressure drop.     

Non-Newtonian tangential flow in cylindrical annuli. IV

Tangential flow of a “power law” model fluid between two concentric cylinders is analyzed. A constant angular pressure gradient is imposed and one of the cylinders is rotating at a constant angular velocity. This type of flow is of interest in screw extrusion theory. The error in the superposition, i.e., linear addition of tangential pressure and drag flows, for a “power law” model fluid, is quantitatively calculated and plotted in the form of a correction factor. Tangential pressure flow is compared to a pressure flow between parallel plates and additional correction factor to account for the curvature is derived and plotted. The applicability of the “power law” model for flow of polymer melts in extruders is also discussed.     

微流量控压钻井水力模型研究

微流量控压钻井是一种以环空流量为监测和控制对象的控压钻井技术,它能够及时发现和控制井下微小的溢流或漏失,减少井下事故的发生。多相流环空压力的计算是微流量控压钻井的关键技术,它关系到整个控压钻井的精确性,文章建立了一种多相流环空压力计算方法和模型,为水力软件的编制和微流量钻井系统的开发设计提供了理论依据。     

Cocurrent gas—liquid flow in packed columns

A model is proposed for cocurrent gas liquid flow through a packed bed. For a given packing, gas and liquid flow rates, we proposed that (i) liquid holdup is a function only of pressure gradient and liquid flow rate and (ii) pressure gradient is only a function of liquid holdup and gas flow rate. Equations are presented which permit the prediction of pressure gradient and liquid holdup for cocurrent upflow and cocurrent downflow in a packed bed. Predictions from the model are shown to be in reasonable agreement with the experimental observations of Turpin and Huntington.     

Modeling of Two‐Phase Flashing Flow of Multicomponent Mixtures in Large Diameter Pipes

A two‐phase flashing flow model is developed to predict the distributions of pressure, temperature, velocity and evaporation rate in a transfer line, which is a typical example of a two‐phase flow pipe in the petrochemical industry. The model is proposed based on the pressure drop model and the multi‐stage flash model. The results indicate that pressure drop, temperature drop, and change of evaporation rate mainly occur in the transition section and the junction site of the transfer line. The predictions of the model have been tested with reliable field data and the good agreement obtained may lead to a better understanding of the two‐phase flashing flow phenomenon, as well as demonstrating the feasibility of applying the model into the design and optimization of pipelines.     

Rigorous design of high pressure natural gas pipelines using bwr equation of state

A model is presented for the prediction of pressure and temperature profiles in a high pressure gas pipeline. Using the BWR equation of state to predict the properties of the gas, an analytical approach reduces the problem to two nonlinear equations which can be solved numerically. Rigorous thermodynamic treatment of the energy and flow equations results in a model which yields good agreement with published data for high pressure natural gas pipelines. The model is also shown to predict frictional heating during the adiabatic flow of dense phase hydrocarbons.     

Mathematical Model for Isothermal Wire-Coating From a Bath of Giesekus Viscoelastic Fluid

A mathematical model of wire-coating based on Giesekus constitutive equation is analyzed under isothermal conditions. It is desired to see the functional dependence of Giesekus model parameters on the important operating variables in the wire-coating process, which include volumetric flow rate (later referred to as flow rate), shear stress at the wire surface (later referred to as shear stress), force required for pulling the wire (later referred to as force), and radius of the coated wire (later referred to as coated wire thickness). To this end, the equation governing the laminar, incompressible, and rectilinear flow is first derived and then solved analytically for the case of vanishing axial pressure gradient. A numerical procedure is described to obtain the solution for the case of nonvanishing pressure gradient. Our results indicate that the magnitude of shear stress and force follow a decreasing trend with increasing Giesekus model parameters in both cases. The flow rate and coated wire thickness decrease on increasing the Giesekus model parameters when there is no imposed pressure gradient. However, in the presence of pressure gradient these variables first decrease with increasing Giesekus model parameters and then follow an increasing trend.     

Online prediction of mass flow rate of solids in dilute phase pneumatic conveying systems using multivariate calibration

Pneumatic conveying systems are used extensively in a wide range of industrial applications. Mass flow rate is one of the most important parameters in this kind of system since it is fundamental for the control of this process and to improve its operation efficiency.A method to predict the mass flow rate of solids in dilute phase conveying is presented in this article. The method uses pressure and air flow rate measurements as variables to calibrate a Partial Least Squares (PLS) regression model, which can be used to predict the mass flow rate of solids from new pressure and air flow rate measurements.Pneumatic conveying tests were carried out with dextrose monohydrate in dilute phase conditions. Independent experimental data from the tests was used to validate the model. The model was successfully validated for a range of different conditions of blow tank pressure and air flow rate. Good agreement with the experimental data was obtained when predicting mass flow rate with all the sensors available in the pneumatic conveying test rig. When using only the air flow rate measurements and two pressure sensors the accuracy of prediction was not affected. The latest suggests the possibility of industrial application, since air flow meters and pressure transmitters are commonly used in industrial settings.