负压分布规律是真空预压机理研究的重要课题。通过讨论真空预压负压空间分布特点及负压相关概念,广义地定义了负压,分析了负压的测量方法及影响因素。设计高15.0 m的竖向大比尺室内模型,开展真空预压负压分布规律试验研究。试验结果表明...负压分布规律是真空预压机理研究的重要课题。通过讨论真空预压负压空间分布特点及负压相关概念,广义地定义了负压,分析了负压的测量方法及影响因素。设计高15.0 m的竖向大比尺室内模型,开展真空预压负压分布规律试验研究。试验结果表明,饱和黏土土中真空度测量存在滞后效应,本次试验真空度存在的极限深度为8.9 m;膜下真空度稳定后,零压面之上孔压及板中真空度沿深度呈对称线性分布,斜率均近似为静水压力梯度;负压沿深度为分段线性分布,在地下水位之上的非饱和段因提水做功而衰减,稳定期负压平均衰减值为21.4 k Pa,在水位之下排水板埋深范围内基本均匀分布而无衰减,稳定期平均负压为-67.0 k Pa。结合试验规律及等效排水管中气液两相流的流型分布,给出了真空预压稳定期竖向排水板中的分段线性负压边界。展开更多
The dynamic behavior of the moving liquid column coalescing with a sessile droplet in triangular microchannels is numerically investigated by using coupled volume of fluid with level set interface tracking method impl...The dynamic behavior of the moving liquid column coalescing with a sessile droplet in triangular microchannels is numerically investigated by using coupled volume of fluid with level set interface tracking method implemented in ANSYS Fluent 14.5 in conjunction with the continuum surface force model. It is found that for both hydrophobic and hydrophilic microchannels, the coalescence between the moving liquid column and droplet can accelerate the original liquid column movement as a result of the induced curvature that lowers the liquid pressure at the interface. As compared to the rectangular microchannel with the same hydraulic diameter, the triangular microchannel exhibits smaller velocity increment ratio because of stronger viscous effect. Simulation results also reveal that the velocity increment ratio increases with the contact angle in hydrophobic microchannels, but it is reverse in the hydrophilic microchannels. The effects of the droplet size, lengthways and transverse positions are also investigated in this work. It is shown that larger droplet and smaller distance between the droplet and inlet or the substrate center can result in larger velocity increment ratio as a result of higher surface energy and lower viscous dissipation energy, respectively. The results obtained in this study create a solid theoretical foundation for designingand optimizing microfluidic devices encountering such a typical phenomenon.展开更多
Numerical simulations are performed both for the single airflow and air-PMtwo-phase flow in wall flow diesel participate filters (DPF) for the first time. The calculationdomain is divided into two regions. In. the inl...Numerical simulations are performed both for the single airflow and air-PMtwo-phase flow in wall flow diesel participate filters (DPF) for the first time. The calculationdomain is divided into two regions. In. the inlet and outlet flow channels, the simulations areperformed for the steady and laminar flow; In the porous filtration walls, the calculation model forflow in porous media is used. The Lagrange two-phase flow model is used to calculate the air-PMflow in DPF, for the dispersed phase (PM), its flow tracks are obtained by the integrating of theLagrange kinetic equation. The calculated velocity, pressure distribution and PM flow tracks in DPFare obtained, which exhibits the main flow characteristics in wall flow DPF and will be help for theoptimal design and performance prediction of wall flow DPF.展开更多
Lattice Boltzmann method(LBM)is a new attractive computational approach for simulating isothermal multi-phase flows in computational fluid dynamics(CFD).It is based on the kinetic theory and easy to be parallelized.Th...Lattice Boltzmann method(LBM)is a new attractive computational approach for simulating isothermal multi-phase flows in computational fluid dynamics(CFD).It is based on the kinetic theory and easy to be parallelized.This study aims to analyze the performance of parallel LBM programming for the incompressible two-phase flows at high density and viscosity ratio.For this purpose,a liquid drop impact on a wetted wall with a pre-existing thin film of the same liquid is simulated by using the parallel LBM code.During the simulations,the domain decomposition,data communication and parallelization of the LBM code using the message passing interface(MPI)library have been investigated.The computational results show that the parallel LBM code exhibits a good high performance computing(HPC)on the parallel speed-up.展开更多
A coupled gas-kinetic scheme(GKS)and unified gas-kinetic wave-particle(UGKWP)method for the disperse dilute gas-particle multiphaseflow is proposed.In the two-phaseflow,the gas phase is always in the hydrodynamic regi...A coupled gas-kinetic scheme(GKS)and unified gas-kinetic wave-particle(UGKWP)method for the disperse dilute gas-particle multiphaseflow is proposed.In the two-phaseflow,the gas phase is always in the hydrodynamic regime and is fol-lowed by GKS for the Navier-Stokes solution.The particle phase is solved by UGKWP in all regimes from particle trajectory crossing to the hydrodynamic wave interac-tion with the variation of particle’s Knudsen number.In the intensive particle colli-sion regime,the UGKWP gives a hydrodynamic wave representation for the particle phase and the GKS-UGKWP for the two-phaseflow reduces to the two-fluid Eulerian-Eulerian(EE)model.In the rarefied regime,the UGKWP tracks individual particle and the GKS-UGKWP goes back to the Eulerian-Lagrangian(EL)formulation.In the tran-sition regime for the solid particle,the GKS-UGKWP takes an optimal choice for the wave and particle decomposition for the solid particle phase and connects the EE and EL methods seamlessly.The GKS-UGKWP method will be tested in allflow regimes with a large variation of Knudsen number for the solid particle transport and Stokes number for the two-phase interaction.It is confirmed that GKS-UGKWP is an efficient and accurate multiscale method for the gas-particle two-phaseflow.展开更多
文摘负压分布规律是真空预压机理研究的重要课题。通过讨论真空预压负压空间分布特点及负压相关概念,广义地定义了负压,分析了负压的测量方法及影响因素。设计高15.0 m的竖向大比尺室内模型,开展真空预压负压分布规律试验研究。试验结果表明,饱和黏土土中真空度测量存在滞后效应,本次试验真空度存在的极限深度为8.9 m;膜下真空度稳定后,零压面之上孔压及板中真空度沿深度呈对称线性分布,斜率均近似为静水压力梯度;负压沿深度为分段线性分布,在地下水位之上的非饱和段因提水做功而衰减,稳定期负压平均衰减值为21.4 k Pa,在水位之下排水板埋深范围内基本均匀分布而无衰减,稳定期平均负压为-67.0 k Pa。结合试验规律及等效排水管中气液两相流的流型分布,给出了真空预压稳定期竖向排水板中的分段线性负压边界。
基金supported by the National Natural Science Foundation of China(5122260351276208 and51325602)+1 种基金the Fundamental Research Funds for the Central Universities(CDJZR12148801)Program for New Century Excellent Talents in University(NCET-12-0591)
文摘The dynamic behavior of the moving liquid column coalescing with a sessile droplet in triangular microchannels is numerically investigated by using coupled volume of fluid with level set interface tracking method implemented in ANSYS Fluent 14.5 in conjunction with the continuum surface force model. It is found that for both hydrophobic and hydrophilic microchannels, the coalescence between the moving liquid column and droplet can accelerate the original liquid column movement as a result of the induced curvature that lowers the liquid pressure at the interface. As compared to the rectangular microchannel with the same hydraulic diameter, the triangular microchannel exhibits smaller velocity increment ratio because of stronger viscous effect. Simulation results also reveal that the velocity increment ratio increases with the contact angle in hydrophobic microchannels, but it is reverse in the hydrophilic microchannels. The effects of the droplet size, lengthways and transverse positions are also investigated in this work. It is shown that larger droplet and smaller distance between the droplet and inlet or the substrate center can result in larger velocity increment ratio as a result of higher surface energy and lower viscous dissipation energy, respectively. The results obtained in this study create a solid theoretical foundation for designingand optimizing microfluidic devices encountering such a typical phenomenon.
文摘Numerical simulations are performed both for the single airflow and air-PMtwo-phase flow in wall flow diesel participate filters (DPF) for the first time. The calculationdomain is divided into two regions. In. the inlet and outlet flow channels, the simulations areperformed for the steady and laminar flow; In the porous filtration walls, the calculation model forflow in porous media is used. The Lagrange two-phase flow model is used to calculate the air-PMflow in DPF, for the dispersed phase (PM), its flow tracks are obtained by the integrating of theLagrange kinetic equation. The calculated velocity, pressure distribution and PM flow tracks in DPFare obtained, which exhibits the main flow characteristics in wall flow DPF and will be help for theoptimal design and performance prediction of wall flow DPF.
基金support by Multiphase Flow for Deep-Sea Oil&Gas Down-hole Applications-SERC TSRP Programme of Agency for Science,Technology and Research(A-STAR)in Singapore(Ref#:1021640075)This work was supported from A"STAR computational resource centre(A'CRC)in Singapore for providing the high performance computing facilities.
文摘Lattice Boltzmann method(LBM)is a new attractive computational approach for simulating isothermal multi-phase flows in computational fluid dynamics(CFD).It is based on the kinetic theory and easy to be parallelized.This study aims to analyze the performance of parallel LBM programming for the incompressible two-phase flows at high density and viscosity ratio.For this purpose,a liquid drop impact on a wetted wall with a pre-existing thin film of the same liquid is simulated by using the parallel LBM code.During the simulations,the domain decomposition,data communication and parallelization of the LBM code using the message passing interface(MPI)library have been investigated.The computational results show that the parallel LBM code exhibits a good high performance computing(HPC)on the parallel speed-up.
基金supported by National Numerical Windtunnel project,National Science Foundation of China(11772281,91852114,12172316)Hong Kong research grant council 16208021Department of Science and Technology of Guangdong Province(Grant No.2020B1212030001).
文摘A coupled gas-kinetic scheme(GKS)and unified gas-kinetic wave-particle(UGKWP)method for the disperse dilute gas-particle multiphaseflow is proposed.In the two-phaseflow,the gas phase is always in the hydrodynamic regime and is fol-lowed by GKS for the Navier-Stokes solution.The particle phase is solved by UGKWP in all regimes from particle trajectory crossing to the hydrodynamic wave interac-tion with the variation of particle’s Knudsen number.In the intensive particle colli-sion regime,the UGKWP gives a hydrodynamic wave representation for the particle phase and the GKS-UGKWP for the two-phaseflow reduces to the two-fluid Eulerian-Eulerian(EE)model.In the rarefied regime,the UGKWP tracks individual particle and the GKS-UGKWP goes back to the Eulerian-Lagrangian(EL)formulation.In the tran-sition regime for the solid particle,the GKS-UGKWP takes an optimal choice for the wave and particle decomposition for the solid particle phase and connects the EE and EL methods seamlessly.The GKS-UGKWP method will be tested in allflow regimes with a large variation of Knudsen number for the solid particle transport and Stokes number for the two-phase interaction.It is confirmed that GKS-UGKWP is an efficient and accurate multiscale method for the gas-particle two-phaseflow.
