Lattice gas and lattice Boltzmann methods are recently developed numerical schemes for simulating a variety of physical systems. In this paper a new lattice Boltzmann model for modeling two-dimensional (2-D) incompressible magnetohydrodynamics (MHD) is presented. The current model fully utilizes the flexibility of the lattice Boltzmann method in comparison with previous lattice gas and lattice Boltzmann MHD models, reducing the number of moving directions from 36 in other models to 12 only. To increase computational efficiency, a simple single time relaxation rule is used for collisions, which directly controls the transport coefficients. The bidirectional streaming process of the particle distribution function in this paper is similar to the original model [H. Chen and W. H. Matthaeus, Phys. Rev. Lett. 58, 1845 (1987), S. Chen et al., Phys. Rev. Lett. 67, 3776 (1991)], but has been greatly simplified, affording simpler implementation of boundary conditions and increasing the feasibility of extension into a workable three-dimensional (3-D) model. Analytical expressions for the transport coefficients are presented. Also, as example cases, numerical calculation for the Hartmann flow is performed, showing a good agreement between the theoretical prediction and numerical simulation, and a sheet-pinch simulation is performed and compared with the results obtained with a spectral method.

Daniel O. Martínez;十一 陈;William H. Matthaeus

Physics of Plasmas

1994

We propose and investigate a new simple fourth order finite difference scheme for the heat equation. Numerical simulations do confirm theoretical analysis of accuracy and stability condition.

Yuehong Qian;Hudong Chen;Raoyang Zhang;十一 陈

Communications in Nonlinear Science and Numerical Simulation

2000

The lattice gas model is extended to include a temperature variable in order to study thermohydrodynamics, the combination of fluid dynamics and heat transfer. The compressible Navier-Stokes equations are derived using a Chapman-Enskog expansion. Heat conduction and convection problems are investigated, including Bénard convection. It is shown that the usual rescaling procedure can be avoided by controlling the temperature.

十一 陈;Hudong Chen;Gary D. Doolen;Semion Gutman;Minxu Lee

Journal of Statistical Physics

1991-3

A program incorporating the parallel code of large eddy simulation (LES) and particle transportation model is developed to simulate the motion of particles in an atmospheric turbulent boundary layer (ATBL). A model of particles of 100-micrometer order coupling with large scale ATBL is proposed. Two typical cases are studied, one focuses on the evolution of particle profile in the ATBL and the landing displacement of particles, whereas the other on the motion of particle stream.

Xiongping Luo;十一 陈

Acta Mechanica Sinica/Lixue Xuebao

2005-6

In this letter, we show via numerical simulations that the typical flow structures appearing in transitional channel flows at moderate Reynolds numbers are not spots but isolated turbulent bands, which have much longer lifetimes than the spots. Localized perturbations can evolve into isolated turbulent bands by continuously growing obliquely when the Reynolds number is larger than 660. However, interactions with other bands and local perturbations cause band breaking and decay. The competition between the band extension and breaking does not lead to a sustained turbulence until Re becomes larger than about 1000. Above this critical value, the bands split, providing an effective mechanism for turbulence spreading.

Xiangming Xiong;建军 陶;十一 陈;Luca Brandt

Physics of Fluids

2015

In this paper, we present an alternative approach for the turbulence modelling in the single-relaxation-time lattice Boltzmann method (LBM) framework by treating the turbulence term as an extra forcing term, in addition to the traditional approach of modifying the relaxation time. We compare these two different approaches and their mixture in large-eddy simulation (LES) of three-dimensional decaying isotropic homogenous turbulence using the Smagorinsky model and the mixed similarity model. When the LES was conducted using the Smagorinsky model, where the Boussinesq eddy-viscosity approximation is adopted, the results showed that these three different implementations are equivalent. However, when the mixed similarity model is adopted, which is beyond the Boussinesq eddy-viscosity approximation, our results showed that an equivalent eddy-viscosity will lead to errors, while the forcing approach is more straightforward and accurate. This provides an alternative and more general framework of simulation of turbulence with models in LBM, especially when the Boussinesq eddy-viscosity approximation is invalid.

Zhenhua Xia;Yipeng Shi;Yu Chen;Moran Wang;十一 陈

Journal of Turbulence

2015-1-2

Cascades of temperature and entropy fluctuations are studied by numerical simulations of stationary three-dimensional compressible turbulence with a heat source. The fluctuation spectra of velocity, compressible velocity component, density and pressure exhibit the -5/3 scaling in an inertial range. The strong acoustic equilibrium relation between spectra of the compressible velocity component and pressure is observed. The -5/3 scaling behaviour is also identified for the fluctuation spectra of temperature and entropy, with the Obukhov-Corrsin constants close to that of a passive scalar spectrum. It is shown by Kovasznay decomposition that the dynamics of the temperature field is dominated by the entropic mode. The average subgrid-scale (SGS) fluxes of temperature and entropy normalized by the total dissipation rates are close to 1 in the inertial range. The cascade of temperature is dominated by the compressible mode of the velocity field, indicating that the theory of a passive scalar in incompressible turbulence is not suitable to describe the inter-scale transfer of temperature in compressible turbulence. In contrast, the cascade of entropy is dominated by the solenoidal mode of the velocity field. The different behaviours of cascades of temperature and entropy are partly explained by the geometrical properties of SGS fluxes. Moreover, the different effects of local compressibility on the SGS fluxes of temperature and entropy are investigated by conditional averaging with respect to the filtered dilatation, demonstrating that the effect of compressibility on the cascade of temperature is much stronger than on the cascade of entropy.

Jianchun Wang;Minping Wan;Song Chen;Chenyue Xie;Lian Ping Wang;十一 陈

Journal of Fluid Mechanics

2019-5-25

Direct numerical simulations of three-dimensional homogeneous turbulence under rapid rigid rotation are conducted for a fixed large reynolds number and a sequence of decreasing rossby numbers to examine the predictions of resonant wave theory. the theory states that 'slow modes' of the velocity, with zero wavenumber parallel to the rotation axis (k_z = 0), will decouple at first order from the remaining 'fast modes' and solve an autonomous system of two-dimensional navier - stokes equations for the horizontal velocity components, normal to the rotation axis, and a two-dimensional passive scalar equation for the vertical velocity component, parallel to the rotation axis. The navier - stokes equation for three-dimensional rotating turbulence is solved in a 128³ mesh after being diagonalized via 'helical decomposition' into normal modes of the coriolis term. A force supplies constant energy input at intermediate scales. to verify the theory, we set up a corresponding simulation for the two-dimensional navier - equation and two-dimensional passive scalar equation to compare them with the slow-mode dynamics of the three-dimensional rotating turbulence. the simulation results reveal that there is a clear inverse energy cascade to the large scales, as predicted by two-dimensional navier - equations for resonant interactions of slow modes. as the rotation rate increases, the vertically averaged horizontal velocity field from three-dimensional Navier-Stokes converges to the velocity field from two-dimensional Navier-Stokes, as measured by the energy in their difference field. likewise, the vertically averaged vertical velocity from three-dimensional Navier-Stokes converges to a solution of the two-dimensional passive scalar equation. the slow-mode energy spectrum approaches K_h^-5/3, where K_h is the horizontal wavenumber, and, as in two dimensions, energy flux becomes closer to constant the greater the rotation rate. furthermore, the energy flux directly into small wavenumbers in the K_h = 0 plane from non-resonant interactions decreases, while fast-mode energy concentrates closer to that plane. the simulations are consistent with an increasingly dominant role of resonant triads for more rapid rotation.

Qiaoning Chen;十一 陈;Gregory L. Eyink;Darryl D. Holm

Journal of Fluid Mechanics

2005-10-11

Compressible magnetohydrodynamic (MHD) turbulence, a model often used to study space and astrophysical plasmas, differs from incompressible magnetohydrodynamic and hydrodynamic (HD) turbulence in many ways. Here direct numerical simulations of mechanically forced compressible MHD turbulence are used to study the degree to which some turbulence theories proposed in the incompressible case remain applicable in the compressible one. Several aspects of compressible turbulence are studied: (i) Intermittency in the compressible case is studied by addressing flows driven with varying forcing mechanisms; these display different features, such as compression and coherent structures. The more compressive simulation is characterized by sheet-like current density structures and shocks, which lead to saturated scaling exponents of high order structure functions of density and compressive velocity. (ii) Further investigations employing conditional averages of different energy transfer fluxes reveal that the influence of shocks (or compressions) makes differences in energy cascade and magnetic amplification. (iii) Cascade is also studied by examining the validity of Yaglom-type relations that verify the scale invariant property within the inertial range, where the transfer is relatively free of the effect of pressure dilation.

Yan Yang;William H. Matthaeus;Yipeng Shi;Minping Wan;十一 陈

Physics of Fluids

2017-3-1

This study investigates the aerodynamic performance of a low-pressure turbine, namely the T106C, by large eddy simulation (LES) and coarse grid direct numerical simulation (CDNS) at a Reynolds number of 100, 000. Existing experimental data were used to validate the computational fluid dynamics (CFD) tool. The effects of subgrid scale (SGS) models, mesh densities, computational domains and boundary conditions on the CFD predictions are studied. On the blade suction surface, a separation zone starts at a location of about 55% along the suction surface. The prediction of flow separation on the turbine blade is always found to be difficult and is one of the focuses of this work. The ability of Smagorinsky and wall-adapting local eddy viscosity (WALE) model in predicting the flow separation is compared. WALE model produces better predictions than the Smagorinsky model. CDNS produces very similar predictions to WALE model. With a finer mesh, the difference due to SGS models becomes smaller. The size of the computational domain is also important. At blade midspan, three-dimensional (3D) features of the separated flow have an effect on the downstream flows, especially for the area near the reattachment. By further considering the effects of endwall secondary flows, a better prediction of the flow separation near the blade midspan can be achieved. The effect of the endwall secondary flow on the blade suction surface separation at the midspan is explained with the analytical method based on the Biot-Savart Law.

Site Hu;Chao Zhou;Zhenhua Xia;十一 陈

Journal of Fluids Engineering, Transactions of the ASME

2018-1