To investigate the slide film damping in the micro-scale shear-driven rarefied gas flows, an effective multi-relaxation-time lattice Boltzmann method(MRT-LBM) is proposed. Through the Knudsen boundary layer model, the...To investigate the slide film damping in the micro-scale shear-driven rarefied gas flows, an effective multi-relaxation-time lattice Boltzmann method(MRT-LBM) is proposed. Through the Knudsen boundary layer model, the effects of wall and rarefaction are considered in the correction of relaxation time. The results of gas velocity distributions are compared among the MRT, Monte Carlo model(DSMC) and high-order LBM, and the effects of the tangential momentum accommodation coefficient on the gas velocity distributions are also compared between the MRT and the high-order LBM. It is indicated that the amendatory MRT-LBM can unlock the dilemma of simulation of micro-scale non-equilibrium. Finally, the effects of the Knudsen number, the Stokes number, and the gap between the plates on the damping are researched. The results show that by decreasing the Knudsen number or increasing the Stokes number, the slide film damping increases in the transition regime;however, as the size of the gap increases, the slide film damping decreases substantially.展开更多
The transition to turbulence in flows where the laminar profile is linearly stable requires perturbations of finite amplitude. ＂Optimal＂ perturbations are distinguished as extrema of certain functionals, and differe...The transition to turbulence in flows where the laminar profile is linearly stable requires perturbations of finite amplitude. ＂Optimal＂ perturbations are distinguished as extrema of certain functionals, and different functionals give different optima. We here discuss the phase space structure of a 2D simplified model of the transition to turbulence and discuss optimal perturbations with respect to three criteria： energy of the initial condition, energy dissipation of the initial condition, and amplitude of noise in a stochastic transition. We find that the states triggering the transition are different in the three cases, but show the same scaling with Reynolds number.展开更多
Mixed convection flow is one of the essential criteria of fluid flow and heat transfer. And its application has been increased due to modernization of society. So, to compete with the global world an analysis has been...Mixed convection flow is one of the essential criteria of fluid flow and heat transfer. And its application has been increased due to modernization of society. So, to compete with the global world an analysis has been investigated numerically. In this study we have considered 2D double lid driven cavity with two-sided adiabatic walls. This problem is illustrated mathematically by a collection of governing equations and the developed model has been solved numerically by using Finite Difference Method (FDM). The goal of the present study is to analyze numerically the thermal behaviour and parameters effect on heat transfer inside the 2D chamber. Also this analysis has been observed for the case where the upper wall is moving at positive direction and lower wall is moving at negative direction with constant speed. Furthermore, we have tried to analyze the velocity and temperature profiles for a vast range of dimensionless parameters namely Reynolds number (Re), Richardson number (Ri)?and Prandtl number?(Pr)?and presented graphically. Moreover, it is found that these flow parameters have significant effects in controlling the flow behavior inside the cavity. A comparison has been done to validate our code and found a good agreement. Finally, average Nusselt number (Nu)?has been studied for the effects of these parameters and presented in tabular form.展开更多
基金The National Natural Science Foundation of China(No.51375091)
文摘To investigate the slide film damping in the micro-scale shear-driven rarefied gas flows, an effective multi-relaxation-time lattice Boltzmann method(MRT-LBM) is proposed. Through the Knudsen boundary layer model, the effects of wall and rarefaction are considered in the correction of relaxation time. The results of gas velocity distributions are compared among the MRT, Monte Carlo model(DSMC) and high-order LBM, and the effects of the tangential momentum accommodation coefficient on the gas velocity distributions are also compared between the MRT and the high-order LBM. It is indicated that the amendatory MRT-LBM can unlock the dilemma of simulation of micro-scale non-equilibrium. Finally, the effects of the Knudsen number, the Stokes number, and the gap between the plates on the damping are researched. The results show that by decreasing the Knudsen number or increasing the Stokes number, the slide film damping increases in the transition regime;however, as the size of the gap increases, the slide film damping decreases substantially.
基金supported in part by the German Research Foundation within FOR 1182
文摘The transition to turbulence in flows where the laminar profile is linearly stable requires perturbations of finite amplitude. ＂Optimal＂ perturbations are distinguished as extrema of certain functionals, and different functionals give different optima. We here discuss the phase space structure of a 2D simplified model of the transition to turbulence and discuss optimal perturbations with respect to three criteria： energy of the initial condition, energy dissipation of the initial condition, and amplitude of noise in a stochastic transition. We find that the states triggering the transition are different in the three cases, but show the same scaling with Reynolds number.
文摘Mixed convection flow is one of the essential criteria of fluid flow and heat transfer. And its application has been increased due to modernization of society. So, to compete with the global world an analysis has been investigated numerically. In this study we have considered 2D double lid driven cavity with two-sided adiabatic walls. This problem is illustrated mathematically by a collection of governing equations and the developed model has been solved numerically by using Finite Difference Method (FDM). The goal of the present study is to analyze numerically the thermal behaviour and parameters effect on heat transfer inside the 2D chamber. Also this analysis has been observed for the case where the upper wall is moving at positive direction and lower wall is moving at negative direction with constant speed. Furthermore, we have tried to analyze the velocity and temperature profiles for a vast range of dimensionless parameters namely Reynolds number (Re), Richardson number (Ri)?and Prandtl number?(Pr)?and presented graphically. Moreover, it is found that these flow parameters have significant effects in controlling the flow behavior inside the cavity. A comparison has been done to validate our code and found a good agreement. Finally, average Nusselt number (Nu)?has been studied for the effects of these parameters and presented in tabular form.
