Lian-Ping Wang | Southern University of Science and Technology (original) (raw)
Papers by Lian-Ping Wang
Atmospheric Chemistry and Physics Discussions, 2014
This paper discusses impacts of cloud and precipitation processes on macrophysical properties of ... more This paper discusses impacts of cloud and precipitation processes on macrophysical properties of shallow convective clouds as simulated by a large-eddy model applying warm-rain bin microphysics. Simulations with and without collision-coalescence are considered with CCN concentrations of 30, 60, 120, and 240 mg<sup>−1</sup>. Simulations with collision-coalescence include either the traditional gravitational collision kernel or a novel kernel that includes enhancements due to the small-scale cloud turbulence. Simulations with droplet collisions were discussed in Wyszogrodzki et al. (2013) focusing on the impact of the turbulent collision kernel. The current paper expands that analysis and puts model results in the context of previous studies. Despite a significant increase of the drizzle/rain with the decrease of CCN concentration, enhanced by the impact of the small-scale turbulence, impacts on the macroscopic cloud field characteristics are relatively minor. We doc...
HAL (Le Centre pour la Communication Scientifique Directe), May 19, 2019
Physics of Fluids
In order to treat immiscible two-phase flows at large density ratios and high Reynolds numbers, a... more In order to treat immiscible two-phase flows at large density ratios and high Reynolds numbers, a three-dimensional code based on the discrete unified gas kinetic scheme (DUGKS) is developed, incorporating two major improvements. First, the particle distribution functions at cell interfaces are reconstructed using a weighted essentially non-oscillatory scheme. Second, the conservative lower-order Allen–Cahn equation is chosen instead of the higher-order Cahn–Hilliard equation to evolve the free-energy-based phase field governing the dynamics of two-phase interfaces. Five benchmark problems are simulated to demonstrate the capability of the approach in treating two-phase flows at large density ratios and high Reynolds numbers, including three two-dimensional problems (a stationary droplet, Rayleigh–Taylor instability, and a droplet splashing on a thin liquid film) and two three-dimensional problems (binary droplets collision and Rayleigh–Taylor instability). All results agree well wi...
In this paper, we present a general framework for the inverse-design of mesoscopic models based o... more In this paper, we present a general framework for the inverse-design of mesoscopic models based on the Boltzmann equation. Starting from the single-relaxation-time Boltzmann equation with an additional source term, two model Boltzmann equations for two reduced distribution functions are obtained, each then also having an additional undetermined source term. Under this general framework and using Navier-Stokes-Fourier (NSF) equations as constraints, the structures of the distribution functions are obtained by the leading-order Chapman-Enskog analysis. Next, five basic constraints for the design of the two source terms are obtained in order to recover the Navier-Stokes-Fourier system in the continuum limit. These constraints allow for adjustable bulk-to-shear viscosity ratio, Prandtl number as well as a thermal energy source. The specific forms of the two source terms can be determined through proper physical considerations and numerical implementation requirements. By employing the t...
Journal of Computational Physics: X, 2021
Physics of Fluids
Bounce-back schemes represent the most popular boundary treatments in the lattice Boltzmann metho... more Bounce-back schemes represent the most popular boundary treatments in the lattice Boltzmann method (LBM) when reproducing the no-slip condition at a solid boundary. While the lattice Boltzmann equation used in LBM for interior nodes is known to reproduce the Navier-Stokes (N-S) equations under the Chapman-Enskog (CE) approximation, the unknown distribution functions reconstructed from a bounce-back scheme at boundary nodes may not be consistent with the CE approximation. This problem could lead to undesirable effects such as non-physical slip velocity, grid-scale velocity and pressure noises, the local inconsistency with the N-S equations, and sometimes even a reduction of the overall numerical-accuracy order of LBM. Here we provide a systematic study of these undesirable effects. We first derive the explicit structure of the mesoscopic distribution function for interior nodes. Then the bounce-back distribution function is examined to identify the hidden errors. It is shown that the...
doi:10.1088/1367-2630/10/7/075013 Abstract. The collision efficiency of sedimenting cloud droplet... more doi:10.1088/1367-2630/10/7/075013 Abstract. The collision efficiency of sedimenting cloud droplets in a turbulent air flow is a key input parameter in predicting the growth of cloud droplets by collision–coalescence. In this study, turbulent collision efficiency was directly computed, using a hybrid direct numerical simulation (HDNS) approach (Ayala et al 2007 J. Comput. Phys. 225 51–73). The HDNS results show that air turbulence enhances the collision efficiency partly due to the fact that aerodynamic interactions (AIs) become less effective in reducing the relative motion of droplets in the presence of background air turbulence. The level of increase in the collision efficiency depends on the flow dissipation rate and the droplet size ratio. For example, the collision efficiency between droplets of 18 and 20µm in radii is increased by air turbulence (relative to the stagnant air case) by a factor of 4 and 1.6 at dissipation rates of 400 and 100 cm2 s−3, respectively. The collision...
Lecture Notes in Computer Science, 2012
New Journal of Physics, 2008
New Journal of Physics, 2008
Journal of Physics: Conference Series, 2011
Kinematic descriptions of the rate of collision between two groups of particles are central to a ... more Kinematic descriptions of the rate of collision between two groups of particles are central to a variety of problems in cloud microphysics, engineering applications, and statistical mechanics. When particles are uniformly distributed, the collision kernel ⌫ depends on the statistics of relative velocities among colliding particles. In the pioneering work by Saffman and Turner ͓"On the collision of drops in turbulent clouds," J. Fluid Mech. 1, 16 ͑1956͔͒, two different formulations were used to calculate ⌫ between two arbitrary particle size groups in a turbulent flow. The first or spherical formulation is based on the radial or longitudinal component w r of the relative velocity w between two particles at contact: ⌫ sph =2R 2 ͉͗w r ͉͘, where R is the geometric collision radius. The second or cylindrical formulation is based on the vector velocity itself: ⌫ cyl = R 2 ͉͗w͉͘. It was shown previously by Wang et al. ͓"Statical mechanical descriptions of turbulent coagulati...
Atmospheric Chemistry and Physics Discussions, 2014
This paper discusses impacts of cloud and precipitation processes on macrophysical properties of ... more This paper discusses impacts of cloud and precipitation processes on macrophysical properties of shallow convective clouds as simulated by a large-eddy model applying warm-rain bin microphysics. Simulations with and without collision-coalescence are considered with CCN concentrations of 30, 60, 120, and 240 mg<sup>−1</sup>. Simulations with collision-coalescence include either the traditional gravitational collision kernel or a novel kernel that includes enhancements due to the small-scale cloud turbulence. Simulations with droplet collisions were discussed in Wyszogrodzki et al. (2013) focusing on the impact of the turbulent collision kernel. The current paper expands that analysis and puts model results in the context of previous studies. Despite a significant increase of the drizzle/rain with the decrease of CCN concentration, enhanced by the impact of the small-scale turbulence, impacts on the macroscopic cloud field characteristics are relatively minor. We doc...
HAL (Le Centre pour la Communication Scientifique Directe), May 19, 2019
Physics of Fluids
In order to treat immiscible two-phase flows at large density ratios and high Reynolds numbers, a... more In order to treat immiscible two-phase flows at large density ratios and high Reynolds numbers, a three-dimensional code based on the discrete unified gas kinetic scheme (DUGKS) is developed, incorporating two major improvements. First, the particle distribution functions at cell interfaces are reconstructed using a weighted essentially non-oscillatory scheme. Second, the conservative lower-order Allen–Cahn equation is chosen instead of the higher-order Cahn–Hilliard equation to evolve the free-energy-based phase field governing the dynamics of two-phase interfaces. Five benchmark problems are simulated to demonstrate the capability of the approach in treating two-phase flows at large density ratios and high Reynolds numbers, including three two-dimensional problems (a stationary droplet, Rayleigh–Taylor instability, and a droplet splashing on a thin liquid film) and two three-dimensional problems (binary droplets collision and Rayleigh–Taylor instability). All results agree well wi...
In this paper, we present a general framework for the inverse-design of mesoscopic models based o... more In this paper, we present a general framework for the inverse-design of mesoscopic models based on the Boltzmann equation. Starting from the single-relaxation-time Boltzmann equation with an additional source term, two model Boltzmann equations for two reduced distribution functions are obtained, each then also having an additional undetermined source term. Under this general framework and using Navier-Stokes-Fourier (NSF) equations as constraints, the structures of the distribution functions are obtained by the leading-order Chapman-Enskog analysis. Next, five basic constraints for the design of the two source terms are obtained in order to recover the Navier-Stokes-Fourier system in the continuum limit. These constraints allow for adjustable bulk-to-shear viscosity ratio, Prandtl number as well as a thermal energy source. The specific forms of the two source terms can be determined through proper physical considerations and numerical implementation requirements. By employing the t...
Journal of Computational Physics: X, 2021
Physics of Fluids
Bounce-back schemes represent the most popular boundary treatments in the lattice Boltzmann metho... more Bounce-back schemes represent the most popular boundary treatments in the lattice Boltzmann method (LBM) when reproducing the no-slip condition at a solid boundary. While the lattice Boltzmann equation used in LBM for interior nodes is known to reproduce the Navier-Stokes (N-S) equations under the Chapman-Enskog (CE) approximation, the unknown distribution functions reconstructed from a bounce-back scheme at boundary nodes may not be consistent with the CE approximation. This problem could lead to undesirable effects such as non-physical slip velocity, grid-scale velocity and pressure noises, the local inconsistency with the N-S equations, and sometimes even a reduction of the overall numerical-accuracy order of LBM. Here we provide a systematic study of these undesirable effects. We first derive the explicit structure of the mesoscopic distribution function for interior nodes. Then the bounce-back distribution function is examined to identify the hidden errors. It is shown that the...
doi:10.1088/1367-2630/10/7/075013 Abstract. The collision efficiency of sedimenting cloud droplet... more doi:10.1088/1367-2630/10/7/075013 Abstract. The collision efficiency of sedimenting cloud droplets in a turbulent air flow is a key input parameter in predicting the growth of cloud droplets by collision–coalescence. In this study, turbulent collision efficiency was directly computed, using a hybrid direct numerical simulation (HDNS) approach (Ayala et al 2007 J. Comput. Phys. 225 51–73). The HDNS results show that air turbulence enhances the collision efficiency partly due to the fact that aerodynamic interactions (AIs) become less effective in reducing the relative motion of droplets in the presence of background air turbulence. The level of increase in the collision efficiency depends on the flow dissipation rate and the droplet size ratio. For example, the collision efficiency between droplets of 18 and 20µm in radii is increased by air turbulence (relative to the stagnant air case) by a factor of 4 and 1.6 at dissipation rates of 400 and 100 cm2 s−3, respectively. The collision...
Lecture Notes in Computer Science, 2012
New Journal of Physics, 2008
New Journal of Physics, 2008
Journal of Physics: Conference Series, 2011
Kinematic descriptions of the rate of collision between two groups of particles are central to a ... more Kinematic descriptions of the rate of collision between two groups of particles are central to a variety of problems in cloud microphysics, engineering applications, and statistical mechanics. When particles are uniformly distributed, the collision kernel ⌫ depends on the statistics of relative velocities among colliding particles. In the pioneering work by Saffman and Turner ͓"On the collision of drops in turbulent clouds," J. Fluid Mech. 1, 16 ͑1956͔͒, two different formulations were used to calculate ⌫ between two arbitrary particle size groups in a turbulent flow. The first or spherical formulation is based on the radial or longitudinal component w r of the relative velocity w between two particles at contact: ⌫ sph =2R 2 ͉͗w r ͉͘, where R is the geometric collision radius. The second or cylindrical formulation is based on the vector velocity itself: ⌫ cyl = R 2 ͉͗w͉͘. It was shown previously by Wang et al. ͓"Statical mechanical descriptions of turbulent coagulati...