The direct numerical simulation (DNS) of heat transfer in a fully developed non-isothermal particle-laden turbulent channel flow is performed. The focus of this paper is on the modulation of the particles on turbule...The direct numerical simulation (DNS) of heat transfer in a fully developed non-isothermal particle-laden turbulent channel flow is performed. The focus of this paper is on the modulation of the particles on turbulent thermal statistics in the particle-laden flow with three Prandtl numbers (Pτ = 0.71, 1.5, and 3.0) and a shear Reynolds number (Reτ = 180). Some typical thermal statistics, including normalized mean temperature and their fluctuations, turbulent heat fluxes, Nusselt number and so on, are analyzed. The results show that the particles have less effects on turbulent thermal fields with the increase of Prandtl number. Two reasons can explain this. First, the correlation between fluid thermal field and velocity field decreases as the Prandtl number increases, and the modulation of turbulent velocity field induced by the particles has less influence on the turbulent thermal field. Second, the heat exchange between turbulence and particles decreases for the particle-laden flow with the larger Prandtl number, and the thermal feedback of the particles to turbulence becomes weak.展开更多
The fluid temperature statistics along particle trajectories is crucial to under-stand the mechanisms of turbulent non-isothermal or reactive fluid-particle flow,especially for the Lagrangian model of non-isothermal p...The fluid temperature statistics along particle trajectories is crucial to under-stand the mechanisms of turbulent non-isothermal or reactive fluid-particle flow,especially for the Lagrangian model of non-isothermal particle-laden turbulent flow.In the present study,direct numerical simulations were utilized to generate temperature field statistics in particle-laden incompressible stationary homogeneous isotropic turbulent flows,which is focused on the effect of particle response time on the Lagrangian statistics of the particle and the fluid temperature seen by particles.It shows that,for the particles withτp/τk<1,the ratio of the fluid intensity seen by particle to fluid temperature intensities deceased asτp/τk increased;while for larger particles(τp/τk>1),the trend is inversed.For small parti-cles(τp/τk<5),the Lagrangian autocorrelation coefficient of the particle temperature R_(p)^(T)decreases as the particle inertia(τp/τk)increases.The trend is reversed for larger particles.The autocorrelation of fluid temperature along the particle path,R_(pf)^(T),decreased as the particle inertia increased.And as the particle inertia increased,the autocorrelation coeffi-cient of the fluid temperature seen by particle decreased more rapidly than that of the particle temperature.The mean temperature gradient contributes to the correlation be-tween the particles velocity component and temperature fluctuations in the direction of the gradient.For the particles withτp/τk<1,the magnitude of the correlation coefficient in-creases as the particle inertia increases,while this value is independent of the particle time constant for larger particles.展开更多
基金Project supported by the National Natural Science Foundation of China(Nos.11272198 and11572183)
文摘The direct numerical simulation (DNS) of heat transfer in a fully developed non-isothermal particle-laden turbulent channel flow is performed. The focus of this paper is on the modulation of the particles on turbulent thermal statistics in the particle-laden flow with three Prandtl numbers (Pτ = 0.71, 1.5, and 3.0) and a shear Reynolds number (Reτ = 180). Some typical thermal statistics, including normalized mean temperature and their fluctuations, turbulent heat fluxes, Nusselt number and so on, are analyzed. The results show that the particles have less effects on turbulent thermal fields with the increase of Prandtl number. Two reasons can explain this. First, the correlation between fluid thermal field and velocity field decreases as the Prandtl number increases, and the modulation of turbulent velocity field induced by the particles has less influence on the turbulent thermal field. Second, the heat exchange between turbulence and particles decreases for the particle-laden flow with the larger Prandtl number, and the thermal feedback of the particles to turbulence becomes weak.
基金This work was partially supported by the State Key Project of Fundamental Research,Ministry of Science and Technology,China(Grant Nos.G1999022207,2002CB211600)the National Natural Science Foundation of China(Grant Nos.50276021,50576027)Program for New Century Excellent Talents in University,Ministry of Education,China(Grant No.NCET-04-0708).
文摘The fluid temperature statistics along particle trajectories is crucial to under-stand the mechanisms of turbulent non-isothermal or reactive fluid-particle flow,especially for the Lagrangian model of non-isothermal particle-laden turbulent flow.In the present study,direct numerical simulations were utilized to generate temperature field statistics in particle-laden incompressible stationary homogeneous isotropic turbulent flows,which is focused on the effect of particle response time on the Lagrangian statistics of the particle and the fluid temperature seen by particles.It shows that,for the particles withτp/τk<1,the ratio of the fluid intensity seen by particle to fluid temperature intensities deceased asτp/τk increased;while for larger particles(τp/τk>1),the trend is inversed.For small parti-cles(τp/τk<5),the Lagrangian autocorrelation coefficient of the particle temperature R_(p)^(T)decreases as the particle inertia(τp/τk)increases.The trend is reversed for larger particles.The autocorrelation of fluid temperature along the particle path,R_(pf)^(T),decreased as the particle inertia increased.And as the particle inertia increased,the autocorrelation coeffi-cient of the fluid temperature seen by particle decreased more rapidly than that of the particle temperature.The mean temperature gradient contributes to the correlation be-tween the particles velocity component and temperature fluctuations in the direction of the gradient.For the particles withτp/τk<1,the magnitude of the correlation coefficient in-creases as the particle inertia increases,while this value is independent of the particle time constant for larger particles.