The effects of Cu addition（0.5%, 1%, 1.5%, 2%, and 3%, mass fraction） on the quality index（Qi） and hot tearing susceptibility（HTS） of A356 alloy were investigated. According to the results, Cu addition up to 1.5...The effects of Cu addition（0.5%, 1%, 1.5%, 2%, and 3%, mass fraction） on the quality index（Qi） and hot tearing susceptibility（HTS） of A356 alloy were investigated. According to the results, Cu addition up to 1.5% increases the Qi by almost 10%, which seems to be due to its solid solution strengthening and dispersion hardening effect of Cu-rich Al2Cu and AlMgCuSi compounds. However, further addition of Cu（up to 3%） decreases the Qi by almost 12%, which is likely due to the reduction of tensile strength and elongation caused by increased volume fraction of brittle Cu-rich intermetallics and microporosities in the microstructure. It is also found that Cu increases the HTS of A356 alloy measured by constrained rod casting method. According to the thermal analysis results, Cu widens the solidification range of the alloy, which in turn, decreases its fluidity and increases the time period during which the mushy-state alloy is exposed to the hot tearing susceptible zone. SEM examination of the hot tear surfaces in high-Cu alloys also demonstrates their rough nature and the occurrence of interdendritic/intergranular microcracks as convincing evidences for the initiation of hot tears in the late stages of solidification in which there is not enough time for crack healing.展开更多
Natural convection in an open end cavity with a hot inclined wall is simulated based on the lattice Boltzmann method （LBM）. The physics of flow and energy transfer in open end cavities are addressed when the hot wal...Natural convection in an open end cavity with a hot inclined wall is simulated based on the lattice Boltzmann method （LBM）. The physics of flow and energy transfer in open end cavities are addressed when the hot wall is inclined. The combination of the two topics （open cavity and inclined walls） is the main novelty of the present study. The effects of the angle of the hot inclined wall on the flow field and heat transfer are thoroughly investigated. The Prandtl number is fixed to 0.71 （air）. The Rayleigh number and the angle of the hot inclined wall are varied in the range of 10^4 to 10^6 and 60° to 85°, respectively. The results are presented for two different aspect ratios, i.e., A = 1 and 2. The results obtained with the LBM are also compared with those of the finite volume method （FVM）. The predicted results of the LBM conform to those of the FVM. The results show that by increasing the angle of the hot inclined wall and the aspect ratio of the cavity, the average Nusselt number decreases. The trend of the local Nusselt number on the inclined wall is also discussed.展开更多
Modeling and direct numerical simulation of particle-laden flows have a tremendous variety of applications in science and engineering across a vast spectrum of scales from pollution dispersion in the atmosphere,to flu...Modeling and direct numerical simulation of particle-laden flows have a tremendous variety of applications in science and engineering across a vast spectrum of scales from pollution dispersion in the atmosphere,to fluidization in the combustion process,to aerosol deposition in spray medication,along with many others.Due to their strongly nonlinear and multiscale nature,the above complex phenomena still raise a very steep challenge to themost computationalmethods.In this review,we provide comprehensive coverage of multibody hydrodynamic(MBH)problems focusing on particulate suspensions in complex fluidic systems that have been simulated using hybrid Eulerian-Lagrangian particulate flow models.Among these hybridmodels,the Immersed Boundary-Lattice Boltzmann Method(IB-LBM)provides mathematically simple and computationally-efficient algorithms for solid-fluid hydrodynamic interactions in MBH simulations.This paper elaborates on the mathematical framework,applicability,and limitations of various’simple to complex’representations of closecontact interparticle interactions and collision methods,including short-range interparticle and particle-wall steric interactions,spring and lubrication forces,normal and oblique collisions,and mesoscale molecular models for deformable particle collisions based on hard-sphere and soft-sphere models in MBH models to simulate settling or flow of nonuniform particles of different geometric shapes and sizes in diverse fluidic systems.展开更多
文摘The effects of Cu addition（0.5%, 1%, 1.5%, 2%, and 3%, mass fraction） on the quality index（Qi） and hot tearing susceptibility（HTS） of A356 alloy were investigated. According to the results, Cu addition up to 1.5% increases the Qi by almost 10%, which seems to be due to its solid solution strengthening and dispersion hardening effect of Cu-rich Al2Cu and AlMgCuSi compounds. However, further addition of Cu（up to 3%） decreases the Qi by almost 12%, which is likely due to the reduction of tensile strength and elongation caused by increased volume fraction of brittle Cu-rich intermetallics and microporosities in the microstructure. It is also found that Cu increases the HTS of A356 alloy measured by constrained rod casting method. According to the thermal analysis results, Cu widens the solidification range of the alloy, which in turn, decreases its fluidity and increases the time period during which the mushy-state alloy is exposed to the hot tearing susceptible zone. SEM examination of the hot tear surfaces in high-Cu alloys also demonstrates their rough nature and the occurrence of interdendritic/intergranular microcracks as convincing evidences for the initiation of hot tears in the late stages of solidification in which there is not enough time for crack healing.
文摘Natural convection in an open end cavity with a hot inclined wall is simulated based on the lattice Boltzmann method （LBM）. The physics of flow and energy transfer in open end cavities are addressed when the hot wall is inclined. The combination of the two topics （open cavity and inclined walls） is the main novelty of the present study. The effects of the angle of the hot inclined wall on the flow field and heat transfer are thoroughly investigated. The Prandtl number is fixed to 0.71 （air）. The Rayleigh number and the angle of the hot inclined wall are varied in the range of 10^4 to 10^6 and 60° to 85°, respectively. The results are presented for two different aspect ratios, i.e., A = 1 and 2. The results obtained with the LBM are also compared with those of the finite volume method （FVM）. The predicted results of the LBM conform to those of the FVM. The results show that by increasing the angle of the hot inclined wall and the aspect ratio of the cavity, the average Nusselt number decreases. The trend of the local Nusselt number on the inclined wall is also discussed.
基金the support of PRIN projects CUP E82F16003010006(principal investigator,G.F.for the Tor Vergata Research Unit)CUP E84I19001020006(principal investigator,G.Bella)financial support fromthe European Research Council under the Horizon 2020 Programme advanced grant agreement no.739964('COPMAT).
文摘Modeling and direct numerical simulation of particle-laden flows have a tremendous variety of applications in science and engineering across a vast spectrum of scales from pollution dispersion in the atmosphere,to fluidization in the combustion process,to aerosol deposition in spray medication,along with many others.Due to their strongly nonlinear and multiscale nature,the above complex phenomena still raise a very steep challenge to themost computationalmethods.In this review,we provide comprehensive coverage of multibody hydrodynamic(MBH)problems focusing on particulate suspensions in complex fluidic systems that have been simulated using hybrid Eulerian-Lagrangian particulate flow models.Among these hybridmodels,the Immersed Boundary-Lattice Boltzmann Method(IB-LBM)provides mathematically simple and computationally-efficient algorithms for solid-fluid hydrodynamic interactions in MBH simulations.This paper elaborates on the mathematical framework,applicability,and limitations of various’simple to complex’representations of closecontact interparticle interactions and collision methods,including short-range interparticle and particle-wall steric interactions,spring and lubrication forces,normal and oblique collisions,and mesoscale molecular models for deformable particle collisions based on hard-sphere and soft-sphere models in MBH models to simulate settling or flow of nonuniform particles of different geometric shapes and sizes in diverse fluidic systems.
