Material flow and phase transformation were studied at the interface of dissimilar joint between Al 6013 and Mg, produced by stir friction welding （FSW） experiments. Defect-free weld was obtained when aluminum and m...Material flow and phase transformation were studied at the interface of dissimilar joint between Al 6013 and Mg, produced by stir friction welding （FSW） experiments. Defect-free weld was obtained when aluminum and magnesium were placed in the advancing side and retreating side respectively and the tool was placed 1 mm off the weld centerline into the aluminum side. In order to understand the material flow during FSW, steel shots were implanted as indexes into the welding path. After welding, using X-ray images, secondary positions of the steel shots were evaluated. It was revealed that steel shots implanted in advancing side were penetrated from the advancing side into the retreating side, whereas the shots implanted in the retreating side remained in the retreating side, without penetrating into the advancing side. The welded specimens were also heat treated. The effects of heat treatment on the mechanical properties of the welds and the formation of new intermetallic layers were investigated. Two intermetallic compounds, Al3Mg2 and Al12Mg17, were formed sequentially at Al6013/Mg interface.展开更多
应用光滑粒子法(SPH)对具有间断面的不同介质的流动问题进行模拟分析.在现有的SPH方法的理论基础上进行修正,通过对密度近似方程进行正则化处理,在理想气体状态方程中引入Van Der Waals修正项以及对物质点运动速度进行修正,模拟了密度...应用光滑粒子法(SPH)对具有间断面的不同介质的流动问题进行模拟分析.在现有的SPH方法的理论基础上进行修正,通过对密度近似方程进行正则化处理,在理想气体状态方程中引入Van Der Waals修正项以及对物质点运动速度进行修正,模拟了密度相差较大的两相流动问题,并且使用图解分析了两相交界面在模拟过程中的清晰程度.通过气(液)泡上升以及两相溃坝问题对SPH方法在两相流动问题模拟中的可行性进行了分析.最后应用修正后的SPH方法有效再现了两相流动的物理过程,并且能清晰分辨不同介质之间的交界面,从而说明SPH方法能有效对两相流动进行模拟.展开更多
The interfacial diffusive contaminant（phosphorus） release from permeable sediment layer into overlying water column under a unidirectional unsteady（periodic） flow condition was experimentally measured and analyzed...The interfacial diffusive contaminant（phosphorus） release from permeable sediment layer into overlying water column under a unidirectional unsteady（periodic） flow condition was experimentally measured and analyzed. The experimental results indicate that the gross diffusive contaminant release rate is substantially enhanced as compared to that under a steady flow condition, and this enhancement trend is much more pronounced in an immediate release stage. The interfacial diffusive contaminant release rate tends to increase with the increasing flow velocity, decreasing period and augmenting amplitude for the case of the unsteady flow. The additional interfacial diffusive contaminant release under the unsteady flow condition may be related to the hydrodynamic response of the diffusive boundary layer to the flow unsteadiness of the overlying water, depending upon not only the periodic thickness variation of the diffusive boundary layer immediately above the sediment-water interface modulated by the temporal flow velocity of the overlying water column but also the intensified turbulent mixing between the overlying water and the pore-water within the superficial sediment layer induced by an alternate acceleration/deceleration fluctuation during each period.展开更多
A compressible lattice Boltzmann-finite difference method is extended by the phase-field approach into a monolithic scheme to study fluid flow and heat transfer through regular arrangements of solid bodies of circular...A compressible lattice Boltzmann-finite difference method is extended by the phase-field approach into a monolithic scheme to study fluid flow and heat transfer through regular arrangements of solid bodies of circular,elliptical and irregular shapes.The advantage of using the phase-field method is demon-strated both in its simplicity of accounting for flow and thermal boundary conditions at solid surfaces with irregular shapes and in the capability of generating such complex-shaped objects.For an array of discs,numerical results for the overall solid-to-gas heat transfer rate are validated via experiments on flow through arrays of hot cylinders.The thus validated compressible LB-FD-PF hybrid scheme is used to study the dependence of heat transfer on flow and thermal boundary conditions(Reynolds number,temperature difference between the hot solid bodies and the inlet gas),porosity as well as on the shape of solid objects.Results are rationalized in terms of the residence time of the gas close to the solid body and downstream variations of gas velocity and temperature.Perspective for further applications of the proposed methodology are also discussed.展开更多
针对流体体积模型(volume of fluid,VOF)在模拟相间传质过程时需要将界面质量流密度转换为单位体积传质速率的问题,对VOF模型中的界面传质与体积传质转换方法进行了改进。提出一种既解决了网格无关性问题又可以反映局部界面传质特性的...针对流体体积模型(volume of fluid,VOF)在模拟相间传质过程时需要将界面质量流密度转换为单位体积传质速率的问题,对VOF模型中的界面传质与体积传质转换方法进行了改进。提出一种既解决了网格无关性问题又可以反映局部界面传质特性的转换方法,并给出了理论推导证明。推导出相应的网格无关性条件,通过划分3组不同尺寸的网格模拟了汽泡冷凝问题,并在汽泡生长方面对该转换方法加以简单应用,模拟结果与理论分析及实验结果符合良好,合理可行,可广泛应用到多相流中界面传热传质模拟的过程。展开更多
This paper describes a novel sharp interface approach for modeling the cavitation phenomena in incompressible viscous flows. A one-field formulation is adopted for the vapor-liquid two-phase flow and the interface is ...This paper describes a novel sharp interface approach for modeling the cavitation phenomena in incompressible viscous flows. A one-field formulation is adopted for the vapor-liquid two-phase flow and the interface is tracked using a volume of fluid（VOF） method. Phase change at the interface is modeled using a simplification of the Rayleigh-Plesset equation. Interface jump conditions in velocity and pressure field are treated using a level set based ghost fluid method. The level set function is constructed from the volume fraction function. A marching cubes method is used to compute the interface area at the interface grid cells. A parallel fast marching method is employed to propagate interface information into the field. A description of the equations and numerical methods is presented. Results for a cavitating hydrofoil are compared with experimental data.展开更多
Whether the particle will be trapped by the solid-liquid interface or not is dependent on its moving behavior ahead of the interface, so a mathematical model has been developed to investigate the movement of the parti...Whether the particle will be trapped by the solid-liquid interface or not is dependent on its moving behavior ahead of the interface, so a mathematical model has been developed to investigate the movement of the particle ahead of the solid-liquid interface. Based on the theory for the boundary layer, the fluid velocity field near the solid-liquid interface was obtained, and the trajectories of particles were calculated by the equations of motion for particles. In this model, the drag force, the added mass force, the buoyance force, the gravitational force, the Saffman force and the Basset history force are considered. The results show that the behavior of the particle ahead of the solid-liquid interface is affected by the physical property of the particle and fluid flow. And in the continuous casting process, if it moves in the stream directed upward or downward near vertical solid-liquid interface or in the horizontal flow under the solid-liquid interface, the particle with the diameter from 5 um to 60um can reach the solid-liquid interface. But if it moves in horizontal flow above the solid-liquid interface, only the particle with the diameter from 5 um to 10 um can reach the solid-liquid interface.展开更多
Viscoelastic flows play an important role in numerous engineering fields,and the multiscale algorithms for simulating viscoelastic flows have received significant attention in order to deepen our understanding of the ...Viscoelastic flows play an important role in numerous engineering fields,and the multiscale algorithms for simulating viscoelastic flows have received significant attention in order to deepen our understanding of the nonlinear dynamic behaviors of viscoelastic fluids.However,traditional grid-based multiscale methods are confined to simple viscoelastic flows with short relaxation time,and there is a lack of uniform multiscale scheme available for coupling different solvers in the simulations of viscoelastic fluids.In this paper,a universal multiscale method coupling an improved smoothed particle hydrodynamics(SPH)and multiscale universal interface(MUI)library is presented for viscoelastic flows.The proposed multiscale method builds on an improved SPH method and leverages the MUI library to facilitate the exchange of information among different solvers in the overlapping domain.We test the capability and flexibility of the presented multiscale method to deal with complex viscoelastic flows by solving different multiscale problems of viscoelastic flows.In the first example,the simulation of a viscoelastic Poiseuille flow is carried out by two coupled improved SPH methods with different spatial resolutions.The effects of exchanging different physical quantities on the numerical results in both the upper and lower domains are also investigated as well as the absolute errors in the overlapping domain.In the second example,the complex Wannier flow with different Weissenberg numbers is further simulated by two improved SPH methods and coupling the improved SPH method and the dissipative particle dynamics(DPD)method.The numerical results show that the physical quantities for viscoelastic flows obtained by the presented multiscale method are in consistence with those obtained by a single solver in the overlapping domain.Moreover,transferring different physical quantities has an important effect on the numerical results.展开更多
The three-dimensional interactions of a perturbed premixed flame interface with a planar incident shock wave and its reflected shock waves are numerically simulated by solving the compressible,reactive Navier-Stokes e...The three-dimensional interactions of a perturbed premixed flame interface with a planar incident shock wave and its reflected shock waves are numerically simulated by solving the compressible,reactive Navier-Stokes equations with the high-resolution scheme and a single-step chemical reaction.The effects of the initial incident shock wave strength (Mach number) and the initial perturbation pattern of interface on the interactions are investigated.The distinct properties of perturbation growth on the flame interface during the interactions are presented.Our results show that perturbation growth is mainly attributed to the flame stretching and propagation.The flame stretching is associated with the larger-scale vortical flow due to RichtmyerMeshkov instability while the flame propagation is due to the chemical reaction.The mixing properties of unburned/burned gases on both sides of the flame are quantitatively analyzed by using integral and statistical diagnostics.The results show that the large-scale flow due to the vortical motion always plays a dominating role during the reactive interaction process;however,the effect of chemistry becomes more important at the later stage of the interactions,especially for higher Mach number cases.The scalar dissipation due to the molecular diffusion is always small in the present study and can be negligible.展开更多
文摘Material flow and phase transformation were studied at the interface of dissimilar joint between Al 6013 and Mg, produced by stir friction welding （FSW） experiments. Defect-free weld was obtained when aluminum and magnesium were placed in the advancing side and retreating side respectively and the tool was placed 1 mm off the weld centerline into the aluminum side. In order to understand the material flow during FSW, steel shots were implanted as indexes into the welding path. After welding, using X-ray images, secondary positions of the steel shots were evaluated. It was revealed that steel shots implanted in advancing side were penetrated from the advancing side into the retreating side, whereas the shots implanted in the retreating side remained in the retreating side, without penetrating into the advancing side. The welded specimens were also heat treated. The effects of heat treatment on the mechanical properties of the welds and the formation of new intermetallic layers were investigated. Two intermetallic compounds, Al3Mg2 and Al12Mg17, were formed sequentially at Al6013/Mg interface.
文摘应用光滑粒子法(SPH)对具有间断面的不同介质的流动问题进行模拟分析.在现有的SPH方法的理论基础上进行修正,通过对密度近似方程进行正则化处理,在理想气体状态方程中引入Van Der Waals修正项以及对物质点运动速度进行修正,模拟了密度相差较大的两相流动问题,并且使用图解分析了两相交界面在模拟过程中的清晰程度.通过气(液)泡上升以及两相溃坝问题对SPH方法在两相流动问题模拟中的可行性进行了分析.最后应用修正后的SPH方法有效再现了两相流动的物理过程,并且能清晰分辨不同介质之间的交界面,从而说明SPH方法能有效对两相流动进行模拟.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11032007,11472168)the Shanghai key Laboratory of mechanics in energy Engineering and Shanghai Program for Innovative Research Team in Universities
文摘The interfacial diffusive contaminant（phosphorus） release from permeable sediment layer into overlying water column under a unidirectional unsteady（periodic） flow condition was experimentally measured and analyzed. The experimental results indicate that the gross diffusive contaminant release rate is substantially enhanced as compared to that under a steady flow condition, and this enhancement trend is much more pronounced in an immediate release stage. The interfacial diffusive contaminant release rate tends to increase with the increasing flow velocity, decreasing period and augmenting amplitude for the case of the unsteady flow. The additional interfacial diffusive contaminant release under the unsteady flow condition may be related to the hydrodynamic response of the diffusive boundary layer to the flow unsteadiness of the overlying water, depending upon not only the periodic thickness variation of the diffusive boundary layer immediately above the sediment-water interface modulated by the temporal flow velocity of the overlying water column but also the intensified turbulent mixing between the overlying water and the pore-water within the superficial sediment layer induced by an alternate acceleration/deceleration fluctuation during each period.
基金funded by the Deutsche For-schungsgemeinschaft(DFG,German Research Foundation)-422037413-CRC/TRR 287"BULK-REACTION".
文摘A compressible lattice Boltzmann-finite difference method is extended by the phase-field approach into a monolithic scheme to study fluid flow and heat transfer through regular arrangements of solid bodies of circular,elliptical and irregular shapes.The advantage of using the phase-field method is demon-strated both in its simplicity of accounting for flow and thermal boundary conditions at solid surfaces with irregular shapes and in the capability of generating such complex-shaped objects.For an array of discs,numerical results for the overall solid-to-gas heat transfer rate are validated via experiments on flow through arrays of hot cylinders.The thus validated compressible LB-FD-PF hybrid scheme is used to study the dependence of heat transfer on flow and thermal boundary conditions(Reynolds number,temperature difference between the hot solid bodies and the inlet gas),porosity as well as on the shape of solid objects.Results are rationalized in terms of the residence time of the gas close to the solid body and downstream variations of gas velocity and temperature.Perspective for further applications of the proposed methodology are also discussed.
文摘针对流体体积模型(volume of fluid,VOF)在模拟相间传质过程时需要将界面质量流密度转换为单位体积传质速率的问题,对VOF模型中的界面传质与体积传质转换方法进行了改进。提出一种既解决了网格无关性问题又可以反映局部界面传质特性的转换方法,并给出了理论推导证明。推导出相应的网格无关性条件,通过划分3组不同尺寸的网格模拟了汽泡冷凝问题,并在汽泡生长方面对该转换方法加以简单应用,模拟结果与理论分析及实验结果符合良好,合理可行,可广泛应用到多相流中界面传热传质模拟的过程。
基金supported by the NSWC Carderock ILIR programby the US Office of Naval Research(Grant No.N000141-01-00-1-7)
文摘This paper describes a novel sharp interface approach for modeling the cavitation phenomena in incompressible viscous flows. A one-field formulation is adopted for the vapor-liquid two-phase flow and the interface is tracked using a volume of fluid（VOF） method. Phase change at the interface is modeled using a simplification of the Rayleigh-Plesset equation. Interface jump conditions in velocity and pressure field are treated using a level set based ghost fluid method. The level set function is constructed from the volume fraction function. A marching cubes method is used to compute the interface area at the interface grid cells. A parallel fast marching method is employed to propagate interface information into the field. A description of the equations and numerical methods is presented. Results for a cavitating hydrofoil are compared with experimental data.
基金This work was supported by the National Natural Science Foundation of China (Grant No. 59734080 and 59504006)the Project of National Fundamental Research and Development of China (Grant No. G1998061510) and High-Tech Research and Development Project
文摘Whether the particle will be trapped by the solid-liquid interface or not is dependent on its moving behavior ahead of the interface, so a mathematical model has been developed to investigate the movement of the particle ahead of the solid-liquid interface. Based on the theory for the boundary layer, the fluid velocity field near the solid-liquid interface was obtained, and the trajectories of particles were calculated by the equations of motion for particles. In this model, the drag force, the added mass force, the buoyance force, the gravitational force, the Saffman force and the Basset history force are considered. The results show that the behavior of the particle ahead of the solid-liquid interface is affected by the physical property of the particle and fluid flow. And in the continuous casting process, if it moves in the stream directed upward or downward near vertical solid-liquid interface or in the horizontal flow under the solid-liquid interface, the particle with the diameter from 5 um to 60um can reach the solid-liquid interface. But if it moves in horizontal flow above the solid-liquid interface, only the particle with the diameter from 5 um to 10 um can reach the solid-liquid interface.
基金Project supported by the National Natural Science Foundation of China(No.52109068)the Water Conservancy Technology Project of Jiangsu Province of China(No.2022060)。
文摘Viscoelastic flows play an important role in numerous engineering fields,and the multiscale algorithms for simulating viscoelastic flows have received significant attention in order to deepen our understanding of the nonlinear dynamic behaviors of viscoelastic fluids.However,traditional grid-based multiscale methods are confined to simple viscoelastic flows with short relaxation time,and there is a lack of uniform multiscale scheme available for coupling different solvers in the simulations of viscoelastic fluids.In this paper,a universal multiscale method coupling an improved smoothed particle hydrodynamics(SPH)and multiscale universal interface(MUI)library is presented for viscoelastic flows.The proposed multiscale method builds on an improved SPH method and leverages the MUI library to facilitate the exchange of information among different solvers in the overlapping domain.We test the capability and flexibility of the presented multiscale method to deal with complex viscoelastic flows by solving different multiscale problems of viscoelastic flows.In the first example,the simulation of a viscoelastic Poiseuille flow is carried out by two coupled improved SPH methods with different spatial resolutions.The effects of exchanging different physical quantities on the numerical results in both the upper and lower domains are also investigated as well as the absolute errors in the overlapping domain.In the second example,the complex Wannier flow with different Weissenberg numbers is further simulated by two improved SPH methods and coupling the improved SPH method and the dissipative particle dynamics(DPD)method.The numerical results show that the physical quantities for viscoelastic flows obtained by the presented multiscale method are in consistence with those obtained by a single solver in the overlapping domain.Moreover,transferring different physical quantities has an important effect on the numerical results.
基金The work was supported by the National Natural Science Foundation of China(11372140).
文摘The three-dimensional interactions of a perturbed premixed flame interface with a planar incident shock wave and its reflected shock waves are numerically simulated by solving the compressible,reactive Navier-Stokes equations with the high-resolution scheme and a single-step chemical reaction.The effects of the initial incident shock wave strength (Mach number) and the initial perturbation pattern of interface on the interactions are investigated.The distinct properties of perturbation growth on the flame interface during the interactions are presented.Our results show that perturbation growth is mainly attributed to the flame stretching and propagation.The flame stretching is associated with the larger-scale vortical flow due to RichtmyerMeshkov instability while the flame propagation is due to the chemical reaction.The mixing properties of unburned/burned gases on both sides of the flame are quantitatively analyzed by using integral and statistical diagnostics.The results show that the large-scale flow due to the vortical motion always plays a dominating role during the reactive interaction process;however,the effect of chemistry becomes more important at the later stage of the interactions,especially for higher Mach number cases.The scalar dissipation due to the molecular diffusion is always small in the present study and can be negligible.
