Particle based methods can be used for both the simulations of solid and fluid phases in multiphase medium, such as the discrete-element method for solid phase and the smoothed particle hydrodynamics for fluid phase. ...Particle based methods can be used for both the simulations of solid and fluid phases in multiphase medium, such as the discrete-element method for solid phase and the smoothed particle hydrodynamics for fluid phase. This paper presents a computational method combining these two methods for solid-liquid medium. The two phases are coupled by using an improved model from a reported Lagrangian-Eulerian method. The technique is verified by simulating liquid-solid flows in a two-dimensional lid-driven cavity.展开更多
The influence of baffle position on liquid sloshing during the braking and turning of a tank truck was studied using a volume of fluid (VOF) model. The forces,their positions and weight distribution during braking and...The influence of baffle position on liquid sloshing during the braking and turning of a tank truck was studied using a volume of fluid (VOF) model. The forces,their positions and weight distribution during braking and the forces and rolling moment during turning were calculated. The reliability of the calculation method was validated by comparisons with experimental results. The results showed that during braking,liquid splashes in the tank and the maximum forces and G (the ratio of weight acting on the front axle to the rear axle) are large when A (the ratio of the arch area above the baffle to the area of cross section)≤0.1. When A≥0.2,as the position of the baffle is lowered,the maximum of Fx (the force in direction x) first decreases then increases,and the maximum of Fy (the force in direction y) and G increase. During turning,liquid splashes in the tank and the maximum forces and M (the rolling moment) are large when D (the ratio of the arch area above the baffle to the area of cross section)≤0.2. When D≥0.3,as the position of the baffle is lowered,the maximums of Fy,Fz (the force in direction z) and M increase.展开更多
The peristaltic pumping of a viscous compressible liquid mixed with rigid spherical particles of the same size in a channel is theoretically investigated. The momentum equations for the compressible flow are solved wi...The peristaltic pumping of a viscous compressible liquid mixed with rigid spherical particles of the same size in a channel is theoretically investigated. The momentum equations for the compressible flow are solved with a perturbation analysis. The analysis is carried out by duly accounting for the nonlinear convective acceleration terms for the fluid part on the wavy wall. The zeroth-order terms yield the Poiseuille flow, and the first-order terms give the Orr-Sommerfeld equation. The explicit expression for the net axial velocity is derived. The effects of the embedded parameters on the axial fluid velocity are studied through different engineering applications. The features of the flow characteristics are analyzed and discussed in detail. The obtained results are evaluated for various parameters associated with the blood flow in the blood vessels with diameters less than 5 500 μm, whereas the particle diameter has been taken to be 8 μm. This study provides a scope to evaluate the effect of the theory of two-phase flow characteristics with compressible fluid problems, and is helpful for understanding the role of engineering applications of pumping solid-fluid mixture by peristaltically driven motion.展开更多
A thin circular liquid sheet can be formed by impinging two identical round jets against each other. The liquid sheet expands to a certain critical radial distance and breaks. The unsteady process of the formation and...A thin circular liquid sheet can be formed by impinging two identical round jets against each other. The liquid sheet expands to a certain critical radial distance and breaks. The unsteady process of the formation and breakup of the liquid sheet in the ambient gas is simulated numerically. Both liquid and gas are treated as incompressible Newtonian fluids. The flow considered is axisymmetric. The liquid-gas interface is modeled with a level set function. A finite difference scheme is used to solve the governing Navier-Stokes equations with physical boundary conditions. The numerical results show how a thin circular sheet can be formed and break at its circular edge in slow motion. The sheet continues to thin as it expands radially. Hence, the Weber number decreases radially. The Weber number is defined as ρu 2 h/σ, where ρ and σ are, respectively, the liquid density and the surface tension, and u and h are, respectively, the average velocity and the half sheet thickness at a local radial location in the liquid sheet. The numerical results show that the sheet indeed terminates at a radial location, where the Weber number reaches one as observed in experiments. The spatio-temporal linear theory predicts that the breakup is initiated by the sinuous mode at the critical Weber number We c =1, below which the absolute instability occurs. The other independent mode called the varicose mode grows more slowly than the sinuous mode according to the linear theory. However, our numerical results show that the varicose mode actually overtakes the sinuous mode during the nonlinear evolution, and is responsible for the final breakup. The linear theory predicts the nature of disturbance waves correctly only at the onset of the instability, but cannot predict the exact consequence of the instability.展开更多
This paper is concerned with three-dimensional numerical simulation of a plunging liquid jet. The transient processes of forming an air cavity around the jet, capturing an initially large air bubble, and the break-up ...This paper is concerned with three-dimensional numerical simulation of a plunging liquid jet. The transient processes of forming an air cavity around the jet, capturing an initially large air bubble, and the break-up of this large toroidal-shaped bubble into smaller bubbles were analyzed. A stabilized finite element method （FEM） was employed under parallel numerical simulations based on adaptive, unstructured grid and coupled with a level-set method to track the interface between air and liquid. These simulations show that the inertia of the liquid jet initially depresses the pool＇s surface, forming an annular air cavity which surrounds the liquid jet. A toroidal liquid eddy which is subse- quently formed in the liquid pool results in air cavity collapse, and in turn entrains air into the liquid pool from the unstable annular air gap region around the liquid jet.展开更多
针对铜吹炼Pierce-Smith转炉(Pierce-Smith Converter,P-S转炉)存在的高能耗及设备维护问题,采用VOF(Volume of Fluid)两相流与Realizable k-ε湍流耦合模型,对炉内气-液两相流行为与壁面剪切应力分布进行数值模拟,系统研究风口直径及...针对铜吹炼Pierce-Smith转炉(Pierce-Smith Converter,P-S转炉)存在的高能耗及设备维护问题,采用VOF(Volume of Fluid)两相流与Realizable k-ε湍流耦合模型,对炉内气-液两相流行为与壁面剪切应力分布进行数值模拟,系统研究风口直径及气体入口速度对熔池动力学的影响机制。研究表明:增大风口直径显著降低搅拌死区体积,扩展高湍动能区域覆盖范围,而提升气体入口速度可增强气泡上升区湍流强度。气体入口速度通过强化局部湍流促进熔池传质效率,风口直径变化可提升炉内混合均匀性。合理选择气体入口速度与风口直径可降低炉壁剪切应力峰值,抑制搅拌死区形成,为工业过程参数优化提供理论依据。展开更多
【目的】鄂尔多斯盆地东缘大宁−吉县区块深部煤层气已实现规模开发,投产水平井近150口,在生产过程中发现随着地层能量逐渐降低,气井携液能力下降,井筒积液成为影响深部煤层气井产量的主要因素之一。深部煤层气游离气和解吸气共同产出,...【目的】鄂尔多斯盆地东缘大宁−吉县区块深部煤层气已实现规模开发,投产水平井近150口,在生产过程中发现随着地层能量逐渐降低,气井携液能力下降,井筒积液成为影响深部煤层气井产量的主要因素之一。深部煤层气游离气和解吸气共同产出,气液比变化大,且不同阶段产气通道及排采工艺不同,适合深部煤层气水平井生产特征的积液诊断预测方法亟需建立,为积液防治提供依据,避免因积液造成储层伤害和产能影响。【方法和结果】基于不可压缩黏性流体的RANSκ-ε方程与volume of fluid method(VOF)方法,利用流体动力学软件Fluent及其二次开发功能,结合深部煤层气水平井油管、环空气液两相流物模实验,构建深部煤层气水平井气液两相流动数值模型,通过数值模拟结果建立适合于深部煤层气水平井不同井筒压力、不同井斜角、圆管条件下和环空条件下的流型图版。基于生产过程中气液两相流动规律及流型演化过程,建立流型与积液的对应关系,得出:泡状流、段塞流对应已发生积液状态,搅混流对应即将发生积液的过渡状态,环状流对应无积液或积液风险较低状态,并且井斜角大小与积液风险成正比,压力与积液风险成反比。【结论】利用积液诊断的流型图版分析法,应用于大宁−吉县区块深部煤层气水平井,指导提出干预时机,及时采取治理措施,措施有效率提高。下一步将引入人工智能技术,向智能分析预测方向进一步优化此方法,为深部煤层气井筒积液预测和防治提供技术支撑。展开更多
In this paper, the feasibility of measuring the gas volume fraction in a mixed gas-liquid flow by using an acoustic resonant spectroscopy (ARS) method in a transient way is studied theoretically and experimentally. Fi...In this paper, the feasibility of measuring the gas volume fraction in a mixed gas-liquid flow by using an acoustic resonant spectroscopy (ARS) method in a transient way is studied theoretically and experimentally. Firstly, the effects of sizes and locations of a single air bubble in a cylindrical cavity with two open ends on resonant frequencies are investigated numerically. Then, a transient measurement system for ARS is established, and the trends of the resonant frequencies (RFs) and resonant amplitudes (RAs) in the cylindrical cavity with gas flux inside are investigated experimentally. The measurement results by the proposed transient method are compared with those by steady-state ones and numerical ones. The numerical results show that the RFs of the cavity are highly sensitive to the volume of the single air bubble. A tiny bubble volume perturbation may cause a prominent RF shift even though the volume of the air bubble is smaller than 0.1% of that of the cavity. When the small air bubble moves, the RF shift will change and reach its maximum value as it is located at the middle of the cavity. As the gas volume fraction of the two-phase flow is low, both the RFs and RAs from the measurement results decrease dramatically with the increasing gas volume, and this decreasing trend gradually becomes even as the gas volume fraction increases further. These experimental results agree with the theoretical ones qualitatively. In addition, the transient method for ARS is more suitable for measuring the gas volume fraction with randomness and instantaneity than the steady-state one, because the latter could not reflect the random and instant characteristics of the mixed fluid due to the time consumption for frequency sweeping. This study will play a very important role in the quantitative measurement of the gas volume fraction of multiphase flows.展开更多
为实现多组分复杂流体流动与扩散耦合过程的准确预测,提出一种耦合多组分Shan-Chen格子玻尔兹曼法(lattice Boltzmann method,LBM)、Maxwell-Stefan扩散通量方程及4参数(临界温度、临界压力、偏心因子和体积修正因子)Peng-Robinson状态...为实现多组分复杂流体流动与扩散耦合过程的准确预测,提出一种耦合多组分Shan-Chen格子玻尔兹曼法(lattice Boltzmann method,LBM)、Maxwell-Stefan扩散通量方程及4参数(临界温度、临界压力、偏心因子和体积修正因子)Peng-Robinson状态方程(equation of state,EOS)的多组分流体流动与扩散耦合模型(equation of state Maxwell-Stefan force model,EOS-MS模型).通过Peng-Robinson EOS计算混合流体整体的流体间作用力,结合多组分LBM中流体间作用力与压力的关系,构建组分流速与流体间作用力的关联,并代入Maxwell-Stefan方程,推导得到各组分受力的代数方程组.利用精确差分法(exact difference method,EDM)将计算得到的组分间作用力引入多组分LBM.分别模拟甲烷、乙烷纯物质及其混合物的气液两相共存问题,计算结果与标准参考数据及逸度平衡法的计算结果一致,验证了模型在预测混合流体热力学平衡态方面的准确性.通过模拟氢气、氮气和二氧化碳的三元扩散动态过程,发现模型结果与有限体积法预测高度吻合,并成功复现了多组分流体中逆扩散等实际扩散现象,证明模型在多组分流体流动与扩散耦合模拟中的有效性.本研究构建的EoS-MS力模型可准确预测多组分流动与扩散耦合过程,避免了在组分受力计算中引入人为假设带来的误差,为解决地热资源利用等领域中存在的多组分复杂流动问题提供了新方法.展开更多
基金supported by Department of Energy and Process Engineering,Norwegian University of Science and TechnologyInstitute for Energy Technology and SINTEF through the FACE(Multiphase Flow Assurance Innovation Center) Project
文摘Particle based methods can be used for both the simulations of solid and fluid phases in multiphase medium, such as the discrete-element method for solid phase and the smoothed particle hydrodynamics for fluid phase. This paper presents a computational method combining these two methods for solid-liquid medium. The two phases are coupled by using an improved model from a reported Lagrangian-Eulerian method. The technique is verified by simulating liquid-solid flows in a two-dimensional lid-driven cavity.
文摘The influence of baffle position on liquid sloshing during the braking and turning of a tank truck was studied using a volume of fluid (VOF) model. The forces,their positions and weight distribution during braking and the forces and rolling moment during turning were calculated. The reliability of the calculation method was validated by comparisons with experimental results. The results showed that during braking,liquid splashes in the tank and the maximum forces and G (the ratio of weight acting on the front axle to the rear axle) are large when A (the ratio of the arch area above the baffle to the area of cross section)≤0.1. When A≥0.2,as the position of the baffle is lowered,the maximum of Fx (the force in direction x) first decreases then increases,and the maximum of Fy (the force in direction y) and G increase. During turning,liquid splashes in the tank and the maximum forces and M (the rolling moment) are large when D (the ratio of the arch area above the baffle to the area of cross section)≤0.2. When D≥0.3,as the position of the baffle is lowered,the maximums of Fy,Fz (the force in direction z) and M increase.
文摘The peristaltic pumping of a viscous compressible liquid mixed with rigid spherical particles of the same size in a channel is theoretically investigated. The momentum equations for the compressible flow are solved with a perturbation analysis. The analysis is carried out by duly accounting for the nonlinear convective acceleration terms for the fluid part on the wavy wall. The zeroth-order terms yield the Poiseuille flow, and the first-order terms give the Orr-Sommerfeld equation. The explicit expression for the net axial velocity is derived. The effects of the embedded parameters on the axial fluid velocity are studied through different engineering applications. The features of the flow characteristics are analyzed and discussed in detail. The obtained results are evaluated for various parameters associated with the blood flow in the blood vessels with diameters less than 5 500 μm, whereas the particle diameter has been taken to be 8 μm. This study provides a scope to evaluate the effect of the theory of two-phase flow characteristics with compressible fluid problems, and is helpful for understanding the role of engineering applications of pumping solid-fluid mixture by peristaltically driven motion.
基金Project supported by the National Natural Science Foundation of China (Nos. 10702038 and10772107)the National Science Foundation of USA (No. CTS-0138057)+1 种基金the Foundation of Science and Technology Commission of Shanghai Municipality (No. 09DZ1141502)the ShanghaiLeading Academic Discipline Project (No. Y0103)
文摘A thin circular liquid sheet can be formed by impinging two identical round jets against each other. The liquid sheet expands to a certain critical radial distance and breaks. The unsteady process of the formation and breakup of the liquid sheet in the ambient gas is simulated numerically. Both liquid and gas are treated as incompressible Newtonian fluids. The flow considered is axisymmetric. The liquid-gas interface is modeled with a level set function. A finite difference scheme is used to solve the governing Navier-Stokes equations with physical boundary conditions. The numerical results show how a thin circular sheet can be formed and break at its circular edge in slow motion. The sheet continues to thin as it expands radially. Hence, the Weber number decreases radially. The Weber number is defined as ρu 2 h/σ, where ρ and σ are, respectively, the liquid density and the surface tension, and u and h are, respectively, the average velocity and the half sheet thickness at a local radial location in the liquid sheet. The numerical results show that the sheet indeed terminates at a radial location, where the Weber number reaches one as observed in experiments. The spatio-temporal linear theory predicts that the breakup is initiated by the sinuous mode at the critical Weber number We c =1, below which the absolute instability occurs. The other independent mode called the varicose mode grows more slowly than the sinuous mode according to the linear theory. However, our numerical results show that the varicose mode actually overtakes the sinuous mode during the nonlinear evolution, and is responsible for the final breakup. The linear theory predicts the nature of disturbance waves correctly only at the onset of the instability, but cannot predict the exact consequence of the instability.
基金supported by the Office of Naval Research(Grant ONRDC14292111)
文摘This paper is concerned with three-dimensional numerical simulation of a plunging liquid jet. The transient processes of forming an air cavity around the jet, capturing an initially large air bubble, and the break-up of this large toroidal-shaped bubble into smaller bubbles were analyzed. A stabilized finite element method （FEM） was employed under parallel numerical simulations based on adaptive, unstructured grid and coupled with a level-set method to track the interface between air and liquid. These simulations show that the inertia of the liquid jet initially depresses the pool＇s surface, forming an annular air cavity which surrounds the liquid jet. A toroidal liquid eddy which is subse- quently formed in the liquid pool results in air cavity collapse, and in turn entrains air into the liquid pool from the unstable annular air gap region around the liquid jet.
文摘针对铜吹炼Pierce-Smith转炉(Pierce-Smith Converter,P-S转炉)存在的高能耗及设备维护问题,采用VOF(Volume of Fluid)两相流与Realizable k-ε湍流耦合模型,对炉内气-液两相流行为与壁面剪切应力分布进行数值模拟,系统研究风口直径及气体入口速度对熔池动力学的影响机制。研究表明:增大风口直径显著降低搅拌死区体积,扩展高湍动能区域覆盖范围,而提升气体入口速度可增强气泡上升区湍流强度。气体入口速度通过强化局部湍流促进熔池传质效率,风口直径变化可提升炉内混合均匀性。合理选择气体入口速度与风口直径可降低炉壁剪切应力峰值,抑制搅拌死区形成,为工业过程参数优化提供理论依据。
文摘【目的】鄂尔多斯盆地东缘大宁−吉县区块深部煤层气已实现规模开发,投产水平井近150口,在生产过程中发现随着地层能量逐渐降低,气井携液能力下降,井筒积液成为影响深部煤层气井产量的主要因素之一。深部煤层气游离气和解吸气共同产出,气液比变化大,且不同阶段产气通道及排采工艺不同,适合深部煤层气水平井生产特征的积液诊断预测方法亟需建立,为积液防治提供依据,避免因积液造成储层伤害和产能影响。【方法和结果】基于不可压缩黏性流体的RANSκ-ε方程与volume of fluid method(VOF)方法,利用流体动力学软件Fluent及其二次开发功能,结合深部煤层气水平井油管、环空气液两相流物模实验,构建深部煤层气水平井气液两相流动数值模型,通过数值模拟结果建立适合于深部煤层气水平井不同井筒压力、不同井斜角、圆管条件下和环空条件下的流型图版。基于生产过程中气液两相流动规律及流型演化过程,建立流型与积液的对应关系,得出:泡状流、段塞流对应已发生积液状态,搅混流对应即将发生积液的过渡状态,环状流对应无积液或积液风险较低状态,并且井斜角大小与积液风险成正比,压力与积液风险成反比。【结论】利用积液诊断的流型图版分析法,应用于大宁−吉县区块深部煤层气水平井,指导提出干预时机,及时采取治理措施,措施有效率提高。下一步将引入人工智能技术,向智能分析预测方向进一步优化此方法,为深部煤层气井筒积液预测和防治提供技术支撑。
基金supported by the National Natural Science Foundation of China (Grant No. 40774099)the National High-tech Research & Devel-opment Program (Grant No. 2008AA06Z205)Special Ocean Com-monweal Research Program (Grant No. 200805005)
文摘In this paper, the feasibility of measuring the gas volume fraction in a mixed gas-liquid flow by using an acoustic resonant spectroscopy (ARS) method in a transient way is studied theoretically and experimentally. Firstly, the effects of sizes and locations of a single air bubble in a cylindrical cavity with two open ends on resonant frequencies are investigated numerically. Then, a transient measurement system for ARS is established, and the trends of the resonant frequencies (RFs) and resonant amplitudes (RAs) in the cylindrical cavity with gas flux inside are investigated experimentally. The measurement results by the proposed transient method are compared with those by steady-state ones and numerical ones. The numerical results show that the RFs of the cavity are highly sensitive to the volume of the single air bubble. A tiny bubble volume perturbation may cause a prominent RF shift even though the volume of the air bubble is smaller than 0.1% of that of the cavity. When the small air bubble moves, the RF shift will change and reach its maximum value as it is located at the middle of the cavity. As the gas volume fraction of the two-phase flow is low, both the RFs and RAs from the measurement results decrease dramatically with the increasing gas volume, and this decreasing trend gradually becomes even as the gas volume fraction increases further. These experimental results agree with the theoretical ones qualitatively. In addition, the transient method for ARS is more suitable for measuring the gas volume fraction with randomness and instantaneity than the steady-state one, because the latter could not reflect the random and instant characteristics of the mixed fluid due to the time consumption for frequency sweeping. This study will play a very important role in the quantitative measurement of the gas volume fraction of multiphase flows.
文摘为实现多组分复杂流体流动与扩散耦合过程的准确预测,提出一种耦合多组分Shan-Chen格子玻尔兹曼法(lattice Boltzmann method,LBM)、Maxwell-Stefan扩散通量方程及4参数(临界温度、临界压力、偏心因子和体积修正因子)Peng-Robinson状态方程(equation of state,EOS)的多组分流体流动与扩散耦合模型(equation of state Maxwell-Stefan force model,EOS-MS模型).通过Peng-Robinson EOS计算混合流体整体的流体间作用力,结合多组分LBM中流体间作用力与压力的关系,构建组分流速与流体间作用力的关联,并代入Maxwell-Stefan方程,推导得到各组分受力的代数方程组.利用精确差分法(exact difference method,EDM)将计算得到的组分间作用力引入多组分LBM.分别模拟甲烷、乙烷纯物质及其混合物的气液两相共存问题,计算结果与标准参考数据及逸度平衡法的计算结果一致,验证了模型在预测混合流体热力学平衡态方面的准确性.通过模拟氢气、氮气和二氧化碳的三元扩散动态过程,发现模型结果与有限体积法预测高度吻合,并成功复现了多组分流体中逆扩散等实际扩散现象,证明模型在多组分流体流动与扩散耦合模拟中的有效性.本研究构建的EoS-MS力模型可准确预测多组分流动与扩散耦合过程,避免了在组分受力计算中引入人为假设带来的误差,为解决地热资源利用等领域中存在的多组分复杂流动问题提供了新方法.
