Large-eddy simulation of wall-bounded turbulent flow with high-order discrete unified gas-kinetic scheme

In this paper,we introduce the discrete Maxwellian equilibrium distribution function for incompressible flow and force term into the two-stage third-order Discrete Unified Gas-Kinetic Scheme(DUGKS)for simulating low-speed turbulent flows.The Wall-Adapting Local Eddy-viscosity(WALE)and Vreman sub-grid models for Large-Eddy Simulations(LES)of turbulent flows are coupled within the present framework.Meanwhile,the implicit LES are also presented to verify the effect of LES models.A parallel implementation strategy for the present framework is developed,and three canonical wall-bounded turbulent flow cases are investigated,including the fully developed turbulent channel flow at a friction Reynolds number(Re)about 180,the turbulent plane Couette flow at a friction Re number about 93 and lid-driven cubical cavity flow at a Re number of 12000.The turbulence statistics,including mean velocity,the r.m.s.fluctuations velocity,Reynolds stress,etc.are computed by the present approach.Their predictions match precisely with each other,and they are both in reasonable agreement with the benchmark data of DNS.Especially,the predicted flow physics of three-dimensional lid-driven cavity flow are consistent with the description from abundant literature.The present numerical results verify that the present two-stage third-order DUGKS-based LES method is capable for simulating inhomogeneous wall-bounded turbulent flows and getting reliable results with relatively coarse grids.

Pseudopotential-based discrete unified gas kinetic scheme for modeling multiphase fluid flows

To directly incorporate the intermolecular interaction effects into the discrete unified gas-kinetic scheme(DUGKS)for simulations of multiphase fluid flow,we developed a pseudopotential-based DUGKS by coupling the pseudopotential model that mimics the intermolecular interaction into DUGKS.Due to the flux reconstruction procedure,additional terms that break the isotropic requirements of the pseudopotential model will be introduced.To eliminate the influences of nonisotropic terms,the expression of equilibrium distribution functions is reformulated in a moment-based form.With the isotropy-preserving parameter appropriately tuned,the nonisotropic effects can be properly canceled out.The fundamental capabilities are validated by the flat interface test and the quiescent droplet test.It has been proved that the proposed pseudopotential-based DUGKS managed to produce and maintain isotropic interfaces.The isotropy-preserving property of pseudopotential-based DUGKS in transient conditions is further confirmed by the spinodal decomposition.Stability superiority of the pseudopotential-based DUGKS over the lattice Boltzmann method is also demonstrated by predicting the coexistence densities complying with the van der Waals equation of state.By directly incorporating the intermolecular interactions,the pseudopotential-based DUGKS offers a mesoscopic perspective of understanding multiphase behaviors,which could help gain fresh insights into multiphase fluid flow.

Application of Lattice Boltzmann Method to Simulation of Compressible Turbulent Flow

The main goal of this paper is to develop the coupled double-distributionfunction(DDF)lattice Boltzmann method(LBM)for simulation of subsonic and transonic turbulent flows.In the present study,we adopt the second-order implicit-explicit(IMEX)Runge-Kutta schemes for time discretization and the Non-Oscillatory and NonFree-Parameters Dissipative(NND)finite difference scheme for space discretization.The Sutherland’s law is used for expressing the viscosity of the fluid due to considerable temperature change.Also,the Spalart-Allmaras(SA)turbulence model is incorporated in order for the turbulent flow effect to be pronounced.Numerical experiments are performed on different turbulent compressible flows around a NACA0012 airfoil with body-fitted grid.Our numerical results are found to be in good agreement with experiment data and/or other numerical solutions,demonstrating the applicability of the method presented in this study to simulations of both subsonic and transonic turbulent flows.