使用热流传感器对氙离子推力器轴向距离为500、700 mm和900 mm,径向角度为0°~15°(推力器出口平面中心为圆心,推力器出口轴线为0°)范围内羽流热流密度的分布进行了实验研究,获得了热流随角度和半径变化的实验数据。采用PI...使用热流传感器对氙离子推力器轴向距离为500、700 mm和900 mm,径向角度为0°~15°(推力器出口平面中心为圆心,推力器出口轴线为0°)范围内羽流热流密度的分布进行了实验研究,获得了热流随角度和半径变化的实验数据。采用PIC-DSMC (particle in cell direct simulation of Monte Carlo)算法在不同适应系数下对实验条件进行仿真分析,对比仿真结果和实验结果得到适应系数。结果表明:keV能量的Xe粒子对热流传感器表面(铜)的适应系数接近1。展开更多
A two-fluid particle-wall collision model with consideration of wall roughness is pro- posed.It takes into account the effects of the friction,restitution and in particular the wall roughness, and hence the redistribu...A two-fluid particle-wall collision model with consideration of wall roughness is pro- posed.It takes into account the effects of the friction,restitution and in particular the wall roughness, and hence the redistribution of Reynolds stress in different directions,the absorption of turbulent en- ergy from the mean motion and the attenuation of particle motion by the wall.The proposed model is used to simulate sudden-expansion and swirling gas-particle flows and is validated by comparing with experimental results.The results show that the proposed model gives better results than those obtained by the presently used zero-gradient condition.Hence,it is suggested that the proposed model should be used as the wall boundary condition for the particle phase in place of the presently used boundary condition.展开更多
We report on discrete element method simulations of a pseudo-two-dimensional （pseudo-2D） fluidized bed to investigate particle-wall interactions. Detailed information on macroscopic flow field variables, including s...We report on discrete element method simulations of a pseudo-two-dimensional （pseudo-2D） fluidized bed to investigate particle-wall interactions. Detailed information on macroscopic flow field variables, including solids pressure, granular temperature, and normal and tangential wall stresses are analyzed. The normal wall stress differs from the solids pressure because of the strong anisotropic flow behavior in the pseudo-2D system. A simple linear relationship exists between normal wall stress and solids pressure. In addition, an effective friction coefficient can be derived to characterize particle-wall flow interaction after evaluating the normal and tangential wall stresses. The effects of inter-particle and particle-wall friction coefficients are evaluated. Strong anisotropic flow behavior in the pseudo-2D system needs to be considered to validate the two-fluid model where the boundary condition is usually developed based on an isotropic assumption. The conclusion has been confirmed by simulation with different particle stiffnesses. Assumptions in the newly developed model for 2D simulation are further examined against the discrete element method simulation.展开更多
This paper describes the use of overlapping grids for the calculation of flow around single and multiple-particle configurations at the micro scale. The basic equations for calculation are those for conservation of ma...This paper describes the use of overlapping grids for the calculation of flow around single and multiple-particle configurations at the micro scale. The basic equations for calculation are those for conservation of mass and momentum which are solved using a common Finite-Volume formulation. The hydrodynamic particle-particle and particle-wall interaction can be calculated by using an overlapping or Chimera grid scheme. With the grid structuring procedure it is possible to use simple and structured grids around the particles and the overall main grid geometry. The particle grids are lapped over the main grid such that they can move independently after each time step without remeshing the whole geometry. The paper gives results for the validation of the code developed for general test cases, for a rotating ellipsoid in simple shear flow, the flow around particles attached to a wall, the motion of a particle in the vicinity of a wall and some results for the flow through a packed bed configuration.展开更多
Three physicalmechanismswhichmay affect dispersion of particle’smotion in wall-bounded turbulent flows,including the effects of turbulence,wall roughness in particle-wall collisions,and inter-particle collisions,are ...Three physicalmechanismswhichmay affect dispersion of particle’smotion in wall-bounded turbulent flows,including the effects of turbulence,wall roughness in particle-wall collisions,and inter-particle collisions,are numerically investigated in this study.Parametric studies with differentwall roughness extents and with different mass loading ratios of particles are performed in fully developed channel flows with the Eulerian-Lagrangian approach.A low-Reynolds-number k−ǫturbulence model is applied for the solution of the carrier-flow field,while the deterministic Lagrangian method together with binary-collision hard-sphere model is applied for the solution of particle motion.It is shown that the mechanism of inter-particle collisions should be taken into account in the modeling except for the flows laden with sufficiently low mass loading ratios of particles.Influences of wall roughness on particle dispersion due to particle-wall collisions are found to be considerable in the bounded particleladen flow.Since the investigated particles are associated with large Stokes numbers,i.e.,larger than O(1),in the test problem,the effects of turbulence on particle dispersion aremuch less considerable,as expected,in comparison with another two physical mechanisms investigated in the study.展开更多
This article investigates the role of the specularity coefficient(φ,the extent of the energy dissipation due to particle-wall collisions),inter-particle restitution coefficient(e_(pp),the extent of the energy dissipa...This article investigates the role of the specularity coefficient(φ,the extent of the energy dissipation due to particle-wall collisions),inter-particle restitution coefficient(e_(pp),the extent of the energy dissipation due to inter-particle collisions),and four combinations of these variables on the hydrodynamics,and the pressure recovery of the dilute gas-solid suspension in a diffuser.The investigation applies the two-fluid modeling approach along with the kinetic theory of the granular flow.The present investigation’s findings indicate that an increase inφor a reduction in e_(pp) reduces the pressure recovery by weakening the reverse momentum transfer phenomenon,which is recognized as the primary means for the pressure recovery.Besides,in a gas-solid flow system,a higherφor smaller e_(pp) enhances the particles’trapping in the recirculation zone.The recirculation zone’s strength and size increase asφincreases or e_(pp) reduces.Moreover,an increase in the wall-particle and inter-particle interactions strengthens the sidewise displacement of the particles.The effect of the wall-particle and inter-particle interactions are insignificant for extremely small solid loading.展开更多
文摘使用热流传感器对氙离子推力器轴向距离为500、700 mm和900 mm,径向角度为0°~15°(推力器出口平面中心为圆心,推力器出口轴线为0°)范围内羽流热流密度的分布进行了实验研究,获得了热流随角度和半径变化的实验数据。采用PIC-DSMC (particle in cell direct simulation of Monte Carlo)算法在不同适应系数下对实验条件进行仿真分析,对比仿真结果和实验结果得到适应系数。结果表明:keV能量的Xe粒子对热流传感器表面(铜)的适应系数接近1。
基金The project supported by the Special Funds for the Major State Basic Research,China (G-1999-0222-08)
文摘A two-fluid particle-wall collision model with consideration of wall roughness is pro- posed.It takes into account the effects of the friction,restitution and in particular the wall roughness, and hence the redistribution of Reynolds stress in different directions,the absorption of turbulent en- ergy from the mean motion and the attenuation of particle motion by the wall.The proposed model is used to simulate sudden-expansion and swirling gas-particle flows and is validated by comparing with experimental results.The results show that the proposed model gives better results than those obtained by the presently used zero-gradient condition.Hence,it is suggested that the proposed model should be used as the wall boundary condition for the particle phase in place of the presently used boundary condition.
文摘We report on discrete element method simulations of a pseudo-two-dimensional （pseudo-2D） fluidized bed to investigate particle-wall interactions. Detailed information on macroscopic flow field variables, including solids pressure, granular temperature, and normal and tangential wall stresses are analyzed. The normal wall stress differs from the solids pressure because of the strong anisotropic flow behavior in the pseudo-2D system. A simple linear relationship exists between normal wall stress and solids pressure. In addition, an effective friction coefficient can be derived to characterize particle-wall flow interaction after evaluating the normal and tangential wall stresses. The effects of inter-particle and particle-wall friction coefficients are evaluated. Strong anisotropic flow behavior in the pseudo-2D system needs to be considered to validate the two-fluid model where the boundary condition is usually developed based on an isotropic assumption. The conclusion has been confirmed by simulation with different particle stiffnesses. Assumptions in the newly developed model for 2D simulation are further examined against the discrete element method simulation.
文摘This paper describes the use of overlapping grids for the calculation of flow around single and multiple-particle configurations at the micro scale. The basic equations for calculation are those for conservation of mass and momentum which are solved using a common Finite-Volume formulation. The hydrodynamic particle-particle and particle-wall interaction can be calculated by using an overlapping or Chimera grid scheme. With the grid structuring procedure it is possible to use simple and structured grids around the particles and the overall main grid geometry. The particle grids are lapped over the main grid such that they can move independently after each time step without remeshing the whole geometry. The paper gives results for the validation of the code developed for general test cases, for a rotating ellipsoid in simple shear flow, the flow around particles attached to a wall, the motion of a particle in the vicinity of a wall and some results for the flow through a packed bed configuration.
基金support by National Science Council,R.O.C.under Grant No.NSC 98-2221-E006-132.
文摘Three physicalmechanismswhichmay affect dispersion of particle’smotion in wall-bounded turbulent flows,including the effects of turbulence,wall roughness in particle-wall collisions,and inter-particle collisions,are numerically investigated in this study.Parametric studies with differentwall roughness extents and with different mass loading ratios of particles are performed in fully developed channel flows with the Eulerian-Lagrangian approach.A low-Reynolds-number k−ǫturbulence model is applied for the solution of the carrier-flow field,while the deterministic Lagrangian method together with binary-collision hard-sphere model is applied for the solution of particle motion.It is shown that the mechanism of inter-particle collisions should be taken into account in the modeling except for the flows laden with sufficiently low mass loading ratios of particles.Influences of wall roughness on particle dispersion due to particle-wall collisions are found to be considerable in the bounded particleladen flow.Since the investigated particles are associated with large Stokes numbers,i.e.,larger than O(1),in the test problem,the effects of turbulence on particle dispersion aremuch less considerable,as expected,in comparison with another two physical mechanisms investigated in the study.
文摘This article investigates the role of the specularity coefficient(φ,the extent of the energy dissipation due to particle-wall collisions),inter-particle restitution coefficient(e_(pp),the extent of the energy dissipation due to inter-particle collisions),and four combinations of these variables on the hydrodynamics,and the pressure recovery of the dilute gas-solid suspension in a diffuser.The investigation applies the two-fluid modeling approach along with the kinetic theory of the granular flow.The present investigation’s findings indicate that an increase inφor a reduction in e_(pp) reduces the pressure recovery by weakening the reverse momentum transfer phenomenon,which is recognized as the primary means for the pressure recovery.Besides,in a gas-solid flow system,a higherφor smaller e_(pp) enhances the particles’trapping in the recirculation zone.The recirculation zone’s strength and size increase asφincreases or e_(pp) reduces.Moreover,an increase in the wall-particle and inter-particle interactions strengthens the sidewise displacement of the particles.The effect of the wall-particle and inter-particle interactions are insignificant for extremely small solid loading.
基金supported by the National Natural Science Foundation of China(Nos.51375446 and 51575494)the Zhejiang Provincial Natural Science Foundation of China(Nos.LR16E050001 and LZ14E050001)
