The Experts below are selected from a list of 318 Experts worldwide ranked by ideXlab platform
Zhaoli Guo - One of the best experts on this subject based on the ideXlab platform.
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discrete unified gas kinetic scheme for all Knudsen Number flows ii thermal compressible case
Physical Review E, 2015Co-Authors: Zhaoli Guo, Ruijie WangAbstract:This paper is a continuation of our work on the development of multiscale numerical scheme from low-speed isothermal flow to compressible flows at high Mach Numbers. In our earlier work [Z. L. Guo et al., Phys. Rev. E 88, 033305 (2013)], a discrete unified gas kinetic scheme (DUGKS) was developed for low-speed flows in which the Mach Number is small so that the flow is nearly incompressible. In the current work, we extend the scheme to compressible flows with the inclusion of thermal effect and shock discontinuity based on the gas kinetic Shakhov model. This method is an explicit finite-volume scheme with the coupling of particle transport and collision in the flux evaluation at a cell interface. As a result, the time step of the method is not limited by the particle collision time. With the variation of the ratio between the time step and particle collision time, the scheme is an asymptotic preserving (AP) method, where both the Chapman-Enskog expansion for the Navier-Stokes solution in the continuum regime and the free transport mechanism in the rarefied limit can be precisely recovered with a second-order accuracy in both space and time. The DUGKS is an idealized multiscale method for all Knudsen Number flow simulations. A Number of numerical tests, including the shock structure problem, the Sod tube problem in a whole range of degree of rarefaction, and the two-dimensional Riemann problem in both continuum and rarefied regimes, are performed to validate the scheme. Comparisons with the results of direct simulation Monte Carlo (DSMC) and other benchmark data demonstrate that the DUGKS is a reliable and efficient method for multiscale flow problems.
Abbas Abbassi - One of the best experts on this subject based on the ideXlab platform.
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reply to comment on heat transfer and fluid flow in microchannels and nanochannels at high Knudsen Number using thermal lattice boltzmann method
Physical Review E, 2011Co-Authors: Jafar Ghazanfarian, Abbas AbbassiAbstract:In this reply to the Comment by Li-Shi Luo, we discuss the results of the lattice Bhatnagar-Gross-Krook (LBGK) model for high-Knudsen-Number (Kn) flow and heat transfer, in the range of Kn 1. We present various studies employing the LBGK model for high-Kn flow and heat transfer simulations. It is concluded that, with the use of the LBGK model in the thermal lattice Boltzmann method for Kn 0.8, some approximations appear in the negative pressure deviation from the linear distribution along the channel. But for Kn < 0.8, the velocity and temperature profiles, compressibility effects, Knudsen layer capturing, and Knudsen paradox phenomenon can be predicted by the LBGK model. We also reject Li-Shi Luo’s claim about the nonconvergence of our numerical scheme by presenting a velocity profile across the channel corresponding to three different high-resolution meshes.
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heat transfer and fluid flow in microchannels and nanochannels at high Knudsen Number using thermal lattice boltzmann method
Physical Review E, 2010Co-Authors: Jafar Ghazanfarian, Abbas AbbassiAbstract:The present paper deals with the two-dimensional numerical simulation of gaseous flow and heat transfer in planar microchannel and nanochannel with different wall temperatures in transitional regime 0.1 ≤ Kn ≤ 1. An atomistic molecular simulation method is used known as thermal lattice-Boltzmann method. The results of simulation are presented in four cases corresponding to the Fourier flow, shear-driven flow (Couette flow), pressure-driven flow (Poiseuille flow), and mixed shear-pressure-driven flow in the developing and fully developed regions. The mixed shear-pressure-driven flow is divided into two subcases with shear stress and pressure gradient acting in the same and the opposite directions. Normalized temperature and velocity profiles across the channel, distribution of local wall Nusselt Number, and friction coefficient are illustrated. Using this method, nonlinear pressure distribution in the streamwise direction, reduction in mass flow rate, C f Re, and Nu by increasing the Knudsen Number are studied. It is seen that for Couette flow, Nu over the hotter plate is greater than the cooler plate, but for the pressure-driven flow with stationary wall temperature dependency of viscosity and thermal conductivity causes this trend to be reversed. The reversed flow appearance in the velocity profile is captured in the case of opposite shear-pressure-driven flow.
Ruijie Wang - One of the best experts on this subject based on the ideXlab platform.
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discrete unified gas kinetic scheme for all Knudsen Number flows ii thermal compressible case
Physical Review E, 2015Co-Authors: Zhaoli Guo, Ruijie WangAbstract:This paper is a continuation of our work on the development of multiscale numerical scheme from low-speed isothermal flow to compressible flows at high Mach Numbers. In our earlier work [Z. L. Guo et al., Phys. Rev. E 88, 033305 (2013)], a discrete unified gas kinetic scheme (DUGKS) was developed for low-speed flows in which the Mach Number is small so that the flow is nearly incompressible. In the current work, we extend the scheme to compressible flows with the inclusion of thermal effect and shock discontinuity based on the gas kinetic Shakhov model. This method is an explicit finite-volume scheme with the coupling of particle transport and collision in the flux evaluation at a cell interface. As a result, the time step of the method is not limited by the particle collision time. With the variation of the ratio between the time step and particle collision time, the scheme is an asymptotic preserving (AP) method, where both the Chapman-Enskog expansion for the Navier-Stokes solution in the continuum regime and the free transport mechanism in the rarefied limit can be precisely recovered with a second-order accuracy in both space and time. The DUGKS is an idealized multiscale method for all Knudsen Number flow simulations. A Number of numerical tests, including the shock structure problem, the Sod tube problem in a whole range of degree of rarefaction, and the two-dimensional Riemann problem in both continuum and rarefied regimes, are performed to validate the scheme. Comparisons with the results of direct simulation Monte Carlo (DSMC) and other benchmark data demonstrate that the DUGKS is a reliable and efficient method for multiscale flow problems.
Yong Cao - One of the best experts on this subject based on the ideXlab platform.
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coupled discrete unified gas kinetic scheme for the thermal compressible flows in all Knudsen Number regimes
Physical Review E, 2018Co-Authors: Hongtao Liu, Mingchi Kong, Qing Chen, Liang Zheng, Yong CaoAbstract:In this paper, a coupled discrete unified gas kinetic scheme (CDUGKS) with a flexible Prandtl Number is developed for the thermal compressible flows in all Knudsen Number regimes. Different from the existing thermal discrete unified gas kinetic scheme based on the Shakhov model, the proposed CDUGKS based on the total energy double-distribution-function model can well preserve the nonnegative property of the distribution function, especially for the strong shock in the continuum regime. In the CDUGKS, the velocity distribution function (VDF) is used to recover the compressible continuity and momentum equations, while the energy distribution function (EDF) is used to recover the energy equation. The VDF and EDF are evaluated in a similar way and then coupled via the thermal equation of state. With the un-splitting treatment of the particle transport and collision in the distribution function evolution and the flux evaluation, the time step in CDUGKS is not limited by the particle collision time. Furthermore, the CDUGKS is an asymptotic preserving scheme, in which the Navier-Stokes solution in the hydrodynamic regime and the free transport mechanism in the kinetic regime can be precisely recovered with the second-order accuracy in both space and time. Finally, several numerical experiments, including the weak shock tube and the strong one in the whole Knudsen Number flows, as well as the two-dimensional Riemann problem and the Rayleigh-Taylor instability in both hydrodynamic regime and kinetic regimes, are performed to validate the method. Numerical results agree fairly well with other benchmark results in different flow regimes, which demonstrates the current CDUGKS is a reliable and efficient method for multiscale flow problems.
Jafar Ghazanfarian - One of the best experts on this subject based on the ideXlab platform.
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reply to comment on heat transfer and fluid flow in microchannels and nanochannels at high Knudsen Number using thermal lattice boltzmann method
Physical Review E, 2011Co-Authors: Jafar Ghazanfarian, Abbas AbbassiAbstract:In this reply to the Comment by Li-Shi Luo, we discuss the results of the lattice Bhatnagar-Gross-Krook (LBGK) model for high-Knudsen-Number (Kn) flow and heat transfer, in the range of Kn 1. We present various studies employing the LBGK model for high-Kn flow and heat transfer simulations. It is concluded that, with the use of the LBGK model in the thermal lattice Boltzmann method for Kn 0.8, some approximations appear in the negative pressure deviation from the linear distribution along the channel. But for Kn < 0.8, the velocity and temperature profiles, compressibility effects, Knudsen layer capturing, and Knudsen paradox phenomenon can be predicted by the LBGK model. We also reject Li-Shi Luo’s claim about the nonconvergence of our numerical scheme by presenting a velocity profile across the channel corresponding to three different high-resolution meshes.
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heat transfer and fluid flow in microchannels and nanochannels at high Knudsen Number using thermal lattice boltzmann method
Physical Review E, 2010Co-Authors: Jafar Ghazanfarian, Abbas AbbassiAbstract:The present paper deals with the two-dimensional numerical simulation of gaseous flow and heat transfer in planar microchannel and nanochannel with different wall temperatures in transitional regime 0.1 ≤ Kn ≤ 1. An atomistic molecular simulation method is used known as thermal lattice-Boltzmann method. The results of simulation are presented in four cases corresponding to the Fourier flow, shear-driven flow (Couette flow), pressure-driven flow (Poiseuille flow), and mixed shear-pressure-driven flow in the developing and fully developed regions. The mixed shear-pressure-driven flow is divided into two subcases with shear stress and pressure gradient acting in the same and the opposite directions. Normalized temperature and velocity profiles across the channel, distribution of local wall Nusselt Number, and friction coefficient are illustrated. Using this method, nonlinear pressure distribution in the streamwise direction, reduction in mass flow rate, C f Re, and Nu by increasing the Knudsen Number are studied. It is seen that for Couette flow, Nu over the hotter plate is greater than the cooler plate, but for the pressure-driven flow with stationary wall temperature dependency of viscosity and thermal conductivity causes this trend to be reversed. The reversed flow appearance in the velocity profile is captured in the case of opposite shear-pressure-driven flow.
