The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
K H Luo - One of the best experts on this subject based on the ideXlab platform.
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three dimensional non orthogonal mrt pseudopotential lattice boltzmann model for Multiphase Flows
Computers & Fluids, 2019Co-Authors: Linlin Fei, K H LuoAbstract:Abstract In the classical multiple-relaxation-time (MRT) lattice Boltzmann (LB) method, the transformation matrix is formed by constructing a set of orthogonal basis vectors. In this paper, a theoretical and numerical study is performed to investigate the capability and efficiency of a non-orthogonal MRT-LB model for simulating Multiphase Flows. First, a three-dimensional non-orthogonal MRT-LB is proposed. A non-orthogonal MRT collision operator is devised based on a set of non-orthogonal basis vectors, through which the transformation matrix and its inverse matrix are considerably simplified as compared with those of an orthogonal MRT collision operator. Furthermore, through the Chapman-Enskog analysis, it is theoretically demonstrated that the three-dimensional non-orthogonal MRT-LB model can correctly recover the macroscopic equations at the Navier-Stokes level in the low Mach number limit. Numerical comparisons between the non-orthogonal MRT-LB model and the usual orthogonal MRT-LB model are made by simulating Multiphase Flows on the basis of the pseudopotential Multiphase LB approach. The numerical results show that, in comparison with the usual orthogonal MRT-LB model, the non-orthogonal MRT-LB model can retain the numerical accuracy while simplifying the implementation.
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modeling realistic Multiphase Flows using a non orthogonal multiple relaxation time lattice boltzmann method
Physics of Fluids, 2019Co-Authors: Linlin Fei, K H Luo, Sauro Succi, Marco Lauricella, Andrea Montessori, Qian WangAbstract:In this paper, we develop a three-dimensional multiple-relaxation-time lattice Boltzmann method (MRT-LBM) based on a set of non-orthogonal basis vectors. Compared with the classical MRT-LBM based on a set of orthogonal basis vectors, the present non-orthogonal MRT-LBM simplifies the transformation between the discrete velocity space and the moment space and exhibits better portability across different lattices. The proposed method is then extended to Multiphase Flows at large density ratio with tunable surface tension, and its numerical stability and accuracy are well demonstrated by some benchmark cases. Using the proposed method, a practical case of a fuel droplet impacting on a dry surface at high Reynolds and Weber numbers is simulated and the evolution of the spreading film diameter agrees well with the experimental data. Furthermore, another realistic case of a droplet impacting on a super-hydrophobic wall with a cylindrical obstacle is reproduced, which confirms the experimental finding of Liu et al. [“Symmetry breaking in drop bouncing on curved surfaces,” Nat. Commun. 6, 10034 (2015)] that the contact time is minimized when the cylinder radius is comparable with the droplet radius.
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lattice boltzmann modeling of Multiphase Flows at large density ratio with an improved pseudopotential model
Physical Review E, 2013Co-Authors: K H LuoAbstract:Owing to its conceptual simplicity and computational efficiency, the pseudopotential Multiphase lattice Boltzmann (LB) model has attracted significant attention since its emergence. In this work, we aim to extend the pseudopotential LB model to simulate Multiphase Flows at large density ratio and relatively high Reynolds number. First, based on our recent work [Q. Li, K. H. Luo, and X. J. Li, Phys. Rev. E 86, 016709 (2012)], an improved forcing scheme is proposed for the multiple-relaxation-time pseudopotential LB model in order to achieve thermodynamic consistency and large density ratio in the model. Next, through investigating the effects of the parameter a in the Carnahan-Starling equation of state, we find that the interface thickness is approximately proportional to 1/√a. Using a smaller a will lead to a wider interface thickness, which can reduce the spurious currents and enhance the numerical stability of the pseudopotential model at large density ratio. Furthermore, it is found that a lower liquid viscosity can be gained in the pseudopotential model by increasing the kinematic viscosity ratio between the vapor and liquid phases. The improved pseudopotential LB model is numerically validated via the simulations of stationary droplet and droplet oscillation. Using the improved model as well as the above treatments, numerical simulations of droplet splashing on a thin liquid film are conducted at a density ratio in excess of 500 with Reynolds numbers ranging from 40 to 1000. The dynamics of droplet splashing is correctly reproduced and the predicted spread radius is found to obey the power law reported in the literature.
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additional interfacial force in lattice boltzmann models for incompressible Multiphase Flows
Physical Review E, 2012Co-Authors: K H Luo, Y J GaoAbstract:The existing lattice Boltzmann models for incompressible Multiphase Flows are mostly constructed with two distribution functions: one is the order parameter distribution function, which is used to track the interface between different phases, and the other is the pressure distribution function for solving the velocity field. In this paper, it is shown that in these models the recovered momentum equation is inconsistent with the target one: an additional force is included in the recovered momentum equation. The additional force has the following features. First, it is proportional to the macroscopic velocity. Second, it is zero in every single-phase region but is nonzero in the interface. Therefore it can be interpreted as an interfacial force. To investigate the effects of the additional interfacial force, numerical simulations are carried out for the problem of Rayleigh-Taylor instability, droplet splashing on a thin liquid film, and the evolution of a falling droplet under gravity. Numerical results demonstrate that, with the increase of the velocity or the Reynolds number, the additional interfacial force will gradually have an important influence on the interface and affect the numerical accuracy.
Jiale Yan - One of the best experts on this subject based on the ideXlab platform.
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higher order nonlocal theory of updated lagrangian particle hydrodynamics ulph and simulations of Multiphase Flows
Computer Methods in Applied Mechanics and Engineering, 2020Co-Authors: Jiale Yan, Aman Zhang, Xingyu Kan, Xin LaiAbstract:Abstract In this work, we present a higher-order nonlocal continuum theory of a recently developed updated Lagrangian particle hydrodynamics (ULPH) (see: Tu and Li, 2017 and Yan et al., 2019) and its applications to Multiphase Flows. The original nonlocal differential operators used in ULPH have only the first-order accuracy, and they may not be able to simulate some complicated and delicate three-dimensional flow problems. In order to improve the computational accuracy and stability, we adopt the nonlocal synchronized differential operator from the reproducing kernel particle method (RKPM), which is regarded as the higher-order nonlocal differential operator, and we apply them to build higher-order ULPH formulations. The main advantage of the higher-order nonlocal differential operator over the original one is its high accuracy in unstructured particle distribution, and it is fully controlled by the approximation polynomial basis. Numerical verifications have been carried out to validate the accuracy of the proposed approach by using various polynomial bases. Several challenging and delicate three-dimensional Multiphase flow benchmark problems are solved to demonstrate the capability of the proposed method. The numerical results of the higher-order ULPH show good agreement with theoretical and numerical solutions in the literature, demonstrating the promising potential of higher-order nonlocal ULPH formulation in modeling and simulating Multiphase Flows with substantial topological variations of interfaces and high density ratios.
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updated lagrangian particle hydrodynamics ulph modeling and simulation of Multiphase Flows
Journal of Computational Physics, 2019Co-Authors: Jiale Yan, Aman Zhang, Xingyu Kan, Pengnan SunAbstract:Abstract In this paper, a weakly compressible updated Lagrangian particle hydrodynamics (ULPH) model [1] has been developed for Multiphase Flows with high density ratios and viscosity ratios. To enhance computation stability and prevent penetrations near the Multiphase flow interface, a new surface tension resultant formulation based on the Continuum Surface Force (CSF) formulation [2] , combined with the interface sharpness force, is also developed within the framework of ULPH method. The intermediate configuration is considered in the computational algorithm, and a modified predictor-corrector scheme is adopted to solve governing equations, which significantly improve the accuracy and efficiency of the ULPH model. Several numerical examples are presented to compare with either analytical or computational results obtained by using different numerical methods such as Smoothed Particle Hydrodynamics (SPH) method, Moving Particle Semi-implicit (MPS) method and Level Set (LS) method within the framework of Finite Element Method (FEM). The results indicate that the ULPH method has good accuracy, stability, and convergence properties in simulations of Multiphase Flows.
Yongping Chen - One of the best experts on this subject based on the ideXlab platform.
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three dimensional pseudopotential lattice boltzmann model for Multiphase Flows at high density ratio
Physical Review E, 2020Co-Authors: Yongping Chen, Longqing ChenAbstract:In this study, we extend the pseudopotential lattice Boltzmann model proposed by Huang and Wu [J. Comput. Phys. 327, 121 (2016)10.1016/j.jcp.2016.09.030] to a three-dimensional model for practical simulations of Multiphase Flows with high density ratio. In this model, an additional source term is introduced into the evolution function, and the performed high-order Chapman-Enskog analysis demonstrates that the Navier-Stokes equations with accurate pressure tensor are recovered. Also, an alternative geometric formulation is developed to obtain various contact angles and an iteration scheme is involved in the initialization to improve the stability of the model. Theoretical and numerical investigations both validate that the thermodynamic consistency and tuning surface tension independently of density ratio is achieved through varying the two free parameters in the source term. Numerical simulations of droplet wetting indicate that a large degree range of contact angles can be precisely realized with the implementation of the wetting boundary scheme. Further dynamic examinations of droplet impingement on a thin film and a dry surface also verify the stability and capability of the proposed pseudopotential lattice Boltzmann model.
Longqing Chen - One of the best experts on this subject based on the ideXlab platform.
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three dimensional pseudopotential lattice boltzmann model for Multiphase Flows at high density ratio
Physical Review E, 2020Co-Authors: Yongping Chen, Longqing ChenAbstract:In this study, we extend the pseudopotential lattice Boltzmann model proposed by Huang and Wu [J. Comput. Phys. 327, 121 (2016)10.1016/j.jcp.2016.09.030] to a three-dimensional model for practical simulations of Multiphase Flows with high density ratio. In this model, an additional source term is introduced into the evolution function, and the performed high-order Chapman-Enskog analysis demonstrates that the Navier-Stokes equations with accurate pressure tensor are recovered. Also, an alternative geometric formulation is developed to obtain various contact angles and an iteration scheme is involved in the initialization to improve the stability of the model. Theoretical and numerical investigations both validate that the thermodynamic consistency and tuning surface tension independently of density ratio is achieved through varying the two free parameters in the source term. Numerical simulations of droplet wetting indicate that a large degree range of contact angles can be precisely realized with the implementation of the wetting boundary scheme. Further dynamic examinations of droplet impingement on a thin film and a dry surface also verify the stability and capability of the proposed pseudopotential lattice Boltzmann model.
C Shu - One of the best experts on this subject based on the ideXlab platform.
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an sph model for Multiphase Flows with complex interfaces and large density differences
Journal of Computational Physics, 2015Co-Authors: Zhen Chen, Zhi Zong, Moubin Liu, Li Zou, C ShuAbstract:In this paper, an improved SPH model for Multiphase Flows with complex interfaces and large density differences is developed. The Multiphase SPH model is based on the assumption of pressure continuity over the interfaces and avoids directly using the information of neighboring particles' densities or masses in solving governing equations. In order to improve computational accuracy and to obtain smooth pressure fields, a corrected density re-initialization is applied. A coupled dynamic solid boundary treatment (SBT) is implemented both to reduce numerical oscillations and to prevent unphysical particle penetration in the boundary area. The density correction and coupled dynamics SBT algorithms are modified to adapt to the density discontinuity on fluid interfaces in Multiphase simulation. A cut-off value of the particle density is set to avoid negative pressure, which can lead to severe numerical difficulties and may even terminate the simulations. Three representative numerical examples, including a Rayleigh-Taylor instability test, a non-Boussinesq problem and a dam breaking simulation, are presented and compared with analytical results or experimental data. It is demonstrated that the present SPH model is capable of modeling complex Multiphase Flows with large interfacial deformations and density ratios.
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Multiphase lattice boltzmann flux solver for incompressible Multiphase Flows with large density ratio
Journal of Computational Physics, 2015Co-Authors: Y. Wang, C Shu, Haibo Huang, C J TeoAbstract:A Multiphase lattice Boltzmann flux solver (MLBFS) is proposed in this paper for incompressible Multiphase Flows with low- and large-density-ratios. In the solver, the flow variables at cell centers are given from the solution of macroscopic governing differential equations (Navier-Stokes equations recovered by Multiphase lattice Boltzmann (LB) model) by the finite volume method. At each cell interface, the viscous and inviscid fluxes are evaluated simultaneously by local reconstruction of solution for the standard lattice Boltzmann equation (LBE). The forcing terms in the governing equations are directly treated by the finite volume discretization. The phase interfaces are captured by solving the phase-field Cahn-Hilliard equation with a fifth order upwind scheme. Unlike the conventional Multiphase LB models, which restrict their applications on uniform grids with fixed time step, the MLBFS has the capability and advantage to simulate Multiphase Flows on non-uniform grids. The proposed solver is validated by several benchmark problems, such as two-phase co-current flow, Taylor-Couette flow in an annulus, Rayleigh-Taylor instability, and droplet splashing on a thin film at density ratio of 1000 with Reynolds numbers ranging from 20 to 1000. Numerical results show the reliability of the proposed solver for Multiphase Flows with high density ratio and high Reynolds number.
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free energy based lattice boltzmann model for the simulation of Multiphase Flows with density contrast
Physical Review E, 2014Co-Authors: J Y Shao, C Shu, Haibo Huang, Y T ChewAbstract:A free-energy-based phase-field lattice Boltzmann method is proposed in this work to simulate Multiphase Flows with density contrast. The present method is to improve the Zheng-Shu-Chew (ZSC) model [Zheng, Shu, and Chew, J. Comput. Phys. 218, 353 (2006)] for correct consideration of density contrast in the momentum equation. The original ZSC model uses the particle distribution function in the lattice Boltzmann equation (LBE) for the mean density and momentum, which cannot properly consider the effect of local density variation in the momentum equation. To correctly consider it, the particle distribution function in the LBE must be for the local density and momentum. However, when the LBE of such distribution function is solved, it will encounter a severe numerical instability. To overcome this difficulty, a transformation, which is similar to the one used in the Lee-Lin (LL) model [Lee and Lin, J. Comput. Phys. 206, 16 (2005)] is introduced in this work to change the particle distribution function for the local density and momentum into that for the mean density and momentum. As a result, the present model still uses the particle distribution function for the mean density and momentum, and in the meantime, considers the effect of local density variation in the LBE as a forcing term. Numerical examples demonstrate that both the present model and the LL model can correctly simulate Multiphase Flows with density contrast, and the present model has an obvious improvement over the ZSC model in terms of solution accuracy. In terms of computational time, the present model is less efficient than the ZSC model, but is much more efficient than the LL model.
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a lattice boltzmann model for Multiphase Flows with large density ratio
Journal of Computational Physics, 2006Co-Authors: H W Zheng, C Shu, Y T ChewAbstract:a lattice Boltzmann model for simulating Multiphase Flows with large density ratios is described in this paper. The method is easily implemented. It does not require solving the Poisson equation and does not involve the complex treatments of derivative terms. The interface capturing equation is recovered without any additional terms as compared to other methods [M.R. Swift, W.R. Osborn, J.M. Yeomans, Lattice Boltzmann simulation of liquid-gas and binary fluid systems, Phys. Rev. E 54 (1996) 5041-5052; T. Inamuro, T. Ogata, S. Tajima, N. Konishi, A lattice Boltzmann method for incompressible two-phase Flows with large density differences, J. Comput. Phys. 198 (2004) 628-644; T. Lee, C.-L. Lin, A stable discretization of the lattice Boltzmann equation for simulation of incompressible two-phase Flows at high density ratio, J. Comput. Phys. 206 (2005) 16-47]. Besides, it requires less discrete velocities. As a result, its efficiency could be greatly improved, especially in 3D applications. It is validated by several cases: a bubble in a stationary flow and the capillary wave. The numerical surface tension obtained from the Laplace law and the interface profile agrees very well with the respective analytical solution. The method is further verified by its application to capillary wave and the bubble rising under buoyancy with comparison to other methods. All the numerical experiments show that the present approach can be used to model Multiphase Flows with large density ratios.
