用“准三维”数值模拟方法研究吹气发泡法制备泡沫铝的过程中,单个气泡在铝熔液搅拌流场中的运动与变形。液体流场采用多重参考系法进行三维模拟,对气泡运动的二维模拟则在三维流场中的一个通过搅拌轴的特征平面上进行。这样既能捕获气...用“准三维”数值模拟方法研究吹气发泡法制备泡沫铝的过程中,单个气泡在铝熔液搅拌流场中的运动与变形。液体流场采用多重参考系法进行三维模拟,对气泡运动的二维模拟则在三维流场中的一个通过搅拌轴的特征平面上进行。这样既能捕获气泡在搅拌流场中运动的基本特征,又能大大降低计算成本。应用流体体积分数(volume of fluid,VOF)方法对气液两相之间的界面进行追踪。通过对不同表面张力气泡的计算,总结出流场中关于气泡运动路径和导致气泡变形直至破碎的三种主要机理。展开更多
Under the absolute coordinate system, the unsteady Reynolds averaged Navier-Stokes(URANS)equations and the k-ω SST turbulence model are solved using the finite volume method to simulate the aerodynamic characteristic...Under the absolute coordinate system, the unsteady Reynolds averaged Navier-Stokes(URANS)equations and the k-ω SST turbulence model are solved using the finite volume method to simulate the aerodynamic characteristics of large seaplane flying with the ground-effect above wavy surface. The velocity inlet wave-making method and the volume of fluid model are used to accurately simulate the linear regular waves and to precisely capture the free surface. This paper studies the influence of the sideslip angle on the aerodynamic characteristics of large seaplane when it is cruising above wavy water. The results show that the wave surface mainly affects the pressure distribution on the lower surface of the wing. When the sideslip angle varies from 0° to 8°,the varying of frequency of aerodynamic forces is consistent with the wave encounter frequency,and both periods are 0.6 s. With the increase of the sideslip angle,the lift coefficient and the pitching moment coefficient decrease. However,when the sideslip angle is smaller than 4°,the decrease amplitude is small,and the significant decrease occurs above 4° and during the whole process of the change of sideslip angle,the aerodynamic fluctuation amplitude is almost unchanged. As the drag coefficient increases with the increase of sideslip angle,significant increase also occurs when the value is greater than4°,and the fluctuation amplitude does not show any correlations. The rolling moment coefficient and yaw moment coefficient increase with the increase of the sideslip angle,and the fluctuation amplitudes of both increase linearly with the increase of the sideslip angle.展开更多
Application of nanofluids in heat pipes usually presents satisfactory experimental results regarding a thermal resistance reduction of the heat pipe.However,the existing computational studies connecting heat pipes and...Application of nanofluids in heat pipes usually presents satisfactory experimental results regarding a thermal resistance reduction of the heat pipe.However,the existing computational studies connecting heat pipes and nanofluids lack a deeper discussion regarding the validity of the models currently used for representing the behaviour of a nanofluid in a heat pipe,particularly for unusual base fluids and nanoparticles such as carbon nanotubes or ethylene glycol.Thus,this comparative study presents the results of a set of computational simulations using pre-established equations for modelling a nanofluid in a heat pipe with experimental data from the literature.The results show agreement with the expected behaviour qualitatively and the presented maximum variations between 1.5% and 23.9% in comparison to the experimentally measured average temperatures.Also,the experimentally obtained temperature distribution of a heat pipe could not be reached numerically only with the use of adequate thermal properties,indicating that the boiling phenomenon is more complex than the current model used for computational simulations.Moreover,the existence of an optimal particle volume fraction for using nanofluids in this application could be observed by combining different properties models.展开更多
Numerical simulations of gas–liquid two-phase flow and alumina transport process in an aluminum reduction cell were conducted to investigate the effects of anode configurations on the bath flow, gas volume fraction a...Numerical simulations of gas–liquid two-phase flow and alumina transport process in an aluminum reduction cell were conducted to investigate the effects of anode configurations on the bath flow, gas volume fraction and alumina content distributions. An Euler–Euler two-fluid model was employed coupled with a species transport equation for alumina content. Three different anode configurations such as anode without a slot, anode with a longitudinal slot and anode with a transversal slot were studied in the simulation. The simulation results clearly show that the slots can reduce the bath velocity and promote the releasing of the anode gas, but can not contribute to the uniformity of the alumina content. Comparisons of the effects between the longitudinal and transversal slots indicate that the longitudinal slot is better in terms of gas–liquid flow but is disadvantageous for alumina mixing and transport process due to a decrease of anode gas under the anode bottom surface. It is demonstrated from the simulations that the mixing and transfer characteristics of alumina are controlled to great extent by the anode gas forces while the electromagnetic forces(EMFs) play the second role.展开更多
Computational fluid dynamics(CFD) has recently emerged as an effective tool for the investigation of the hydraulic parameters and efficiency of tray towers.The computation domain was established for two types of orien...Computational fluid dynamics(CFD) has recently emerged as an effective tool for the investigation of the hydraulic parameters and efficiency of tray towers.The computation domain was established for two types of oriented valves within a tray and meshed into two parts with different grid types and sizes.The volume fraction correlation concerning inter-phase momentum transfer source was fitted based on experimental data,and built in UDF for simulation.The flow pattern of oriented valve tray under different operating conditions was simulated under Eulerian-Eulerian framework with realizable k-ε model.The predicted liquid height from CFD simulation was in good agreement with the results of pressure drop and volume fraction correlations.Meanwhile,the velocity distribution and volume fraction of the two phases were demonstrated and analyzed,which are useful in design and analysis of the column trays.展开更多
The hydrodynamic behavior in a high-density downer reactor was studied. A two-fluid model based on the kinetic theory of granular flow with a k-ε turbulent model was developed to simulate the flow behavior in the sys...The hydrodynamic behavior in a high-density downer reactor was studied. A two-fluid model based on the kinetic theory of granular flow with a k-ε turbulent model was developed to simulate the flow behavior in the system. This simulation achieved an averaged solid fraction in the bed as high as 18% in this operating regime. The flow development in high-density downer consists of 3 regions, which are first acceleration, second acceleration, and fully developed regions. In the fully developed region, the lateral distribution of the solid volume fraction is low and almost uniform in the center region with a high density peak near the wall region. Gas and solid velocities gradually increase toward the wall and form a peak near the wall region. In addition, the solid volume fraction, gas and solid velocities increase with solid circulation rate.展开更多
Based on the gas-liquid two-phase mixture transportation test, the k-c-A; turbulence model was applied to simulate the two-phase turbulent flow in a vortex pump. By comparing the simulation and experiment results, inn...Based on the gas-liquid two-phase mixture transportation test, the k-c-A; turbulence model was applied to simulate the two-phase turbulent flow in a vortex pump. By comparing the simulation and experiment results, inner flow features were revealed. The bubbles in the channel distribute mainly at the pressure side of the blades, and the aggregation degree of the bubbles is enhanced with an increase in inlet gas volume fraction. Experimental results indicate that the influence of the gas phase on vortex pump performance is small when the gas volume fraction is less than 10%. When the gas volume fraction contiuuously increases to 15%, the characteristic curves abruptly drop due to the gas blocking phenomenon.展开更多
A multi-lattice deterministic trajectory(MLDT) model is developed to simulate dense gas-particle flow in a vertical channel.The actual inter-particle collision and particle motion are treated by a Lagrangian model wit...A multi-lattice deterministic trajectory(MLDT) model is developed to simulate dense gas-particle flow in a vertical channel.The actual inter-particle collision and particle motion are treated by a Lagrangian model with three sets of lattices to reduce computational time.Cluster formation and motion near the wall are successfully predicted with mean particle volume fraction and velocity,showing quantitatively agreement with experimental results.The mechanism of particles concentrated near the wall is investigated by considering effects of gravity,particle-wall collisions,inter-particle collisions and velocity profiles of the gas phase.It is shown that the inter-particle collision and gas-phase velocity distribution are the essential factors for cluster formation near the wall,while gravity and particle-wall collision only have minor effects on particle concentration near the wall.Particles are unable to remain in the high velocity region due to the strong inter-particle collisions,while they tend to stay in the low velocity region for weak inter-particle collisions.In addition,the effects of channel width and particle sizes on cluster formation are also investigated and it is found that particle concentration near the wall reduces with the decrease of channel width and increase of particle size.展开更多
文摘用“准三维”数值模拟方法研究吹气发泡法制备泡沫铝的过程中,单个气泡在铝熔液搅拌流场中的运动与变形。液体流场采用多重参考系法进行三维模拟,对气泡运动的二维模拟则在三维流场中的一个通过搅拌轴的特征平面上进行。这样既能捕获气泡在搅拌流场中运动的基本特征,又能大大降低计算成本。应用流体体积分数(volume of fluid,VOF)方法对气液两相之间的界面进行追踪。通过对不同表面张力气泡的计算,总结出流场中关于气泡运动路径和导致气泡变形直至破碎的三种主要机理。
文摘Under the absolute coordinate system, the unsteady Reynolds averaged Navier-Stokes(URANS)equations and the k-ω SST turbulence model are solved using the finite volume method to simulate the aerodynamic characteristics of large seaplane flying with the ground-effect above wavy surface. The velocity inlet wave-making method and the volume of fluid model are used to accurately simulate the linear regular waves and to precisely capture the free surface. This paper studies the influence of the sideslip angle on the aerodynamic characteristics of large seaplane when it is cruising above wavy water. The results show that the wave surface mainly affects the pressure distribution on the lower surface of the wing. When the sideslip angle varies from 0° to 8°,the varying of frequency of aerodynamic forces is consistent with the wave encounter frequency,and both periods are 0.6 s. With the increase of the sideslip angle,the lift coefficient and the pitching moment coefficient decrease. However,when the sideslip angle is smaller than 4°,the decrease amplitude is small,and the significant decrease occurs above 4° and during the whole process of the change of sideslip angle,the aerodynamic fluctuation amplitude is almost unchanged. As the drag coefficient increases with the increase of sideslip angle,significant increase also occurs when the value is greater than4°,and the fluctuation amplitude does not show any correlations. The rolling moment coefficient and yaw moment coefficient increase with the increase of the sideslip angle,and the fluctuation amplitudes of both increase linearly with the increase of the sideslip angle.
基金CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico of Brazil) for the scholarship to Prof. Rodrigo Vidonscky Pinto.
文摘Application of nanofluids in heat pipes usually presents satisfactory experimental results regarding a thermal resistance reduction of the heat pipe.However,the existing computational studies connecting heat pipes and nanofluids lack a deeper discussion regarding the validity of the models currently used for representing the behaviour of a nanofluid in a heat pipe,particularly for unusual base fluids and nanoparticles such as carbon nanotubes or ethylene glycol.Thus,this comparative study presents the results of a set of computational simulations using pre-established equations for modelling a nanofluid in a heat pipe with experimental data from the literature.The results show agreement with the expected behaviour qualitatively and the presented maximum variations between 1.5% and 23.9% in comparison to the experimentally measured average temperatures.Also,the experimentally obtained temperature distribution of a heat pipe could not be reached numerically only with the use of adequate thermal properties,indicating that the boiling phenomenon is more complex than the current model used for computational simulations.Moreover,the existence of an optimal particle volume fraction for using nanofluids in this application could be observed by combining different properties models.
基金Project(2010AA065201)supported by the High Technology Research and Development Program of ChinaProject(2013zzts038)supported by the Fundamental Research Funds for the Central Universities of ChinaProject(ZB2011CBBCe1)supported by the Major Program for Aluminum Corporation of China Limited,China
文摘Numerical simulations of gas–liquid two-phase flow and alumina transport process in an aluminum reduction cell were conducted to investigate the effects of anode configurations on the bath flow, gas volume fraction and alumina content distributions. An Euler–Euler two-fluid model was employed coupled with a species transport equation for alumina content. Three different anode configurations such as anode without a slot, anode with a longitudinal slot and anode with a transversal slot were studied in the simulation. The simulation results clearly show that the slots can reduce the bath velocity and promote the releasing of the anode gas, but can not contribute to the uniformity of the alumina content. Comparisons of the effects between the longitudinal and transversal slots indicate that the longitudinal slot is better in terms of gas–liquid flow but is disadvantageous for alumina mixing and transport process due to a decrease of anode gas under the anode bottom surface. It is demonstrated from the simulations that the mixing and transfer characteristics of alumina are controlled to great extent by the anode gas forces while the electromagnetic forces(EMFs) play the second role.
文摘Computational fluid dynamics(CFD) has recently emerged as an effective tool for the investigation of the hydraulic parameters and efficiency of tray towers.The computation domain was established for two types of oriented valves within a tray and meshed into two parts with different grid types and sizes.The volume fraction correlation concerning inter-phase momentum transfer source was fitted based on experimental data,and built in UDF for simulation.The flow pattern of oriented valve tray under different operating conditions was simulated under Eulerian-Eulerian framework with realizable k-ε model.The predicted liquid height from CFD simulation was in good agreement with the results of pressure drop and volume fraction correlations.Meanwhile,the velocity distribution and volume fraction of the two phases were demonstrated and analyzed,which are useful in design and analysis of the column trays.
文摘The hydrodynamic behavior in a high-density downer reactor was studied. A two-fluid model based on the kinetic theory of granular flow with a k-ε turbulent model was developed to simulate the flow behavior in the system. This simulation achieved an averaged solid fraction in the bed as high as 18% in this operating regime. The flow development in high-density downer consists of 3 regions, which are first acceleration, second acceleration, and fully developed regions. In the fully developed region, the lateral distribution of the solid volume fraction is low and almost uniform in the center region with a high density peak near the wall region. Gas and solid velocities gradually increase toward the wall and form a peak near the wall region. In addition, the solid volume fraction, gas and solid velocities increase with solid circulation rate.
基金supported by the National Natural Science Foundation of China (No50879080, No 50609025 and No 50735004)Zhejiang Provincial Key Science Foundation of China (No2008C01024-1 and No2008C21023)
文摘Based on the gas-liquid two-phase mixture transportation test, the k-c-A; turbulence model was applied to simulate the two-phase turbulent flow in a vortex pump. By comparing the simulation and experiment results, inner flow features were revealed. The bubbles in the channel distribute mainly at the pressure side of the blades, and the aggregation degree of the bubbles is enhanced with an increase in inlet gas volume fraction. Experimental results indicate that the influence of the gas phase on vortex pump performance is small when the gas volume fraction is less than 10%. When the gas volume fraction contiuuously increases to 15%, the characteristic curves abruptly drop due to the gas blocking phenomenon.
基金partially supported by the National Basic Research Program of China ("973" Project) (Grant No. 62980532)
文摘A multi-lattice deterministic trajectory(MLDT) model is developed to simulate dense gas-particle flow in a vertical channel.The actual inter-particle collision and particle motion are treated by a Lagrangian model with three sets of lattices to reduce computational time.Cluster formation and motion near the wall are successfully predicted with mean particle volume fraction and velocity,showing quantitatively agreement with experimental results.The mechanism of particles concentrated near the wall is investigated by considering effects of gravity,particle-wall collisions,inter-particle collisions and velocity profiles of the gas phase.It is shown that the inter-particle collision and gas-phase velocity distribution are the essential factors for cluster formation near the wall,while gravity and particle-wall collision only have minor effects on particle concentration near the wall.Particles are unable to remain in the high velocity region due to the strong inter-particle collisions,while they tend to stay in the low velocity region for weak inter-particle collisions.In addition,the effects of channel width and particle sizes on cluster formation are also investigated and it is found that particle concentration near the wall reduces with the decrease of channel width and increase of particle size.
