The micro- and macro-time scales in two-phase turbulent channel flows are investigated using the direct nu- merical simulation and the Lagrangian particle trajectory methods for the fluid- and the particle-phases, res...The micro- and macro-time scales in two-phase turbulent channel flows are investigated using the direct nu- merical simulation and the Lagrangian particle trajectory methods for the fluid- and the particle-phases, respectively. Lagrangian and Eulerian time scales of both phases are cal- culated using velocity correlation functions. Due to flow anisotropy, micro-time scales are not the same with the theo- retical estimations in large Reynolds number （isotropic） tur- bulence. Lagrangian macro-time scales of particle-phase and of fluid-phase seen by particles are both dependent on particle Stokes number. The fluid-phase Lagrangian inte- gral time scales increase with distance from the wall, longer than those time scales seen by particles. The Eulerian inte- gral macro-time scales increase in near-wall regions but de- crease in out-layer regions. The moving Eulerian time scales are also investigated and compared with Lagrangian integral time scales, and in good agreement with previous measure- ments and numerical predictions. For the fluid particles the micro Eulerian time scales are longer than the Lagrangian ones in the near wall regions, while away from the walls the micro Lagrangian time scales are longer. The Lagrangian integral time scales are longer than the Eulerian ones. The results are useful for further understanding two-phase flow physics and especially for constructing accurate prediction models of inertial particle dispersion.展开更多
Granular materials exhibit abundant dissipations due to fluctuations in both granular motions and configurations （i.e., granular skeleton） evolutions. Twin granular temperatures Tk and T~ are introduced accounting f...Granular materials exhibit abundant dissipations due to fluctuations in both granular motions and configurations （i.e., granular skeleton） evolutions. Twin granular temperatures Tk and T~ are introduced accounting for two types of fluctuations, and the so-called twin granular temperatures theory is established as an extension of granular solid hydrodynamics. By using simulations, the nonaffine deformations in a 2D assembly are simulated by using discrete element methods. By analogizing with microdamages in deformed solids, double scalar damage variables, Dp and Dq, are proposed to describe the deformed granular solid under triaxial compressions. Granular flows are found intrinsically turbulent due to the presence of Tk and the Naiver Stokes equation is obtained for granular flows.展开更多
Pulsating turbulent open channel flow has been investigated by the use ofLarge Eddy Simulation (LES) tech-nique coupled with dynamic Sub-Grid-Scale (SGS) model for turbulentSGS stress to closure the governing equation...Pulsating turbulent open channel flow has been investigated by the use ofLarge Eddy Simulation (LES) tech-nique coupled with dynamic Sub-Grid-Scale (SGS) model for turbulentSGS stress to closure the governing equations. Three-dimensional filtered Navier-Stokes equationsare numerically solved by a fractional — step method. The objective of this study is to deal withthe behavior of the pulsating turbulent open channel flow and to examine the reliability of the LESapproach for predicting the pulsating turbulent flow. In this study, the Reynolds number (Re_τ) ischosen as 180 based on the friction velocity and the channel depth. The frequency of the drivingpressure gradient for the pulsating turbulent flow ranges low, medium and high value. Statisticalturbulence quantities as well as the flow structures are analyzed.展开更多
基金supported by the National Natural Science Foundation of China (11132005 and 50706021)
文摘The micro- and macro-time scales in two-phase turbulent channel flows are investigated using the direct nu- merical simulation and the Lagrangian particle trajectory methods for the fluid- and the particle-phases, respectively. Lagrangian and Eulerian time scales of both phases are cal- culated using velocity correlation functions. Due to flow anisotropy, micro-time scales are not the same with the theo- retical estimations in large Reynolds number （isotropic） tur- bulence. Lagrangian macro-time scales of particle-phase and of fluid-phase seen by particles are both dependent on particle Stokes number. The fluid-phase Lagrangian inte- gral time scales increase with distance from the wall, longer than those time scales seen by particles. The Eulerian inte- gral macro-time scales increase in near-wall regions but de- crease in out-layer regions. The moving Eulerian time scales are also investigated and compared with Lagrangian integral time scales, and in good agreement with previous measure- ments and numerical predictions. For the fluid particles the micro Eulerian time scales are longer than the Lagrangian ones in the near wall regions, while away from the walls the micro Lagrangian time scales are longer. The Lagrangian integral time scales are longer than the Eulerian ones. The results are useful for further understanding two-phase flow physics and especially for constructing accurate prediction models of inertial particle dispersion.
文摘Granular materials exhibit abundant dissipations due to fluctuations in both granular motions and configurations （i.e., granular skeleton） evolutions. Twin granular temperatures Tk and T~ are introduced accounting for two types of fluctuations, and the so-called twin granular temperatures theory is established as an extension of granular solid hydrodynamics. By using simulations, the nonaffine deformations in a 2D assembly are simulated by using discrete element methods. By analogizing with microdamages in deformed solids, double scalar damage variables, Dp and Dq, are proposed to describe the deformed granular solid under triaxial compressions. Granular flows are found intrinsically turbulent due to the presence of Tk and the Naiver Stokes equation is obtained for granular flows.
文摘Pulsating turbulent open channel flow has been investigated by the use ofLarge Eddy Simulation (LES) tech-nique coupled with dynamic Sub-Grid-Scale (SGS) model for turbulentSGS stress to closure the governing equations. Three-dimensional filtered Navier-Stokes equationsare numerically solved by a fractional — step method. The objective of this study is to deal withthe behavior of the pulsating turbulent open channel flow and to examine the reliability of the LESapproach for predicting the pulsating turbulent flow. In this study, the Reynolds number (Re_τ) ischosen as 180 based on the friction velocity and the channel depth. The frequency of the drivingpressure gradient for the pulsating turbulent flow ranges low, medium and high value. Statisticalturbulence quantities as well as the flow structures are analyzed.
