Multiple-relaxation-time Lattice Boltzmann Method Research Articles

634 MRT格子ボルツマン法によるダクト内流れのLES(OS8.流体の数値計算手法と数値シミュレーション(2),オーガナイズドセッション)

634 MRT格子ボルツマン法によるダクト内流れのLES(OS8.流体の数値計算手法と数値シミュレーション(2),オーガナイズドセッション)

Bifurcation phenomenon in the wake of a 3-D cylinder

Numerical simulations are carried out for a long slender rigid circular cylinder in a cross flow to investigate the effect of end-plates on the bifurcation phenomenon in the near wake. A multiple relaxation time lattice Boltzmann method (MRT-LBM) is used for the solution of three-dimensional unsteady flow. At the Reynolds number of 200, there exists shedding frequency bifurcation along the span which is resulted from the shedding phase oscillation.

Multiple-relaxation time lattice Boltzmann method for the finite Knudsen number region

A multiple-relaxation time lattice Boltzmann model discretized with second order trapezoid rule in a coherent framework is presented for the finite Knudsen number region. Combination of bounce back and specular reflection boundary condition is implemented at the walls, which gives tunable second order slip coefficient as it is shown by the analysis of the boundary condition. Plane channel flow is simulated in good agreement with the analytical derivation and predictions, which demonstrates the applicability of the present approach for microfluidic applications.

Three-dimensional wake interactions for two side-by-side cylinders in a cross flow

Three-dimensional (3D) flow over two side-by-side circular cylinders is numerically studied for understanding the complex wake interference behind the cylinder pair. The two cylinders are bounded by two spanwise end plates. A multiple-relaxation-time lattice Boltzmann method (MRT-LBM) is used for the solution of 3D unsteady flow. The simulations are carried out with Reynolds number Re = 200, aspect ratio L/D = 16 and four transverse pitch ratios: T/D = 1.2, 1.5, 2.0 and 3.0, where Re is defined by incoming velocity U, cylinder diameter D and kinetic viscosity ν, L is cylinder span length and T is center to center spacing between the cylinder pair. Numerical results show that the wake patterns depend on not only Re and T/D, but also the end-flow conditions. At T/D = 2.0, the mutual interference between the two cylinders leads to two flip–flopping vortex streets; with the gap flow biased randomly, intermittently towards one cylinder or the other. Both the wake street and statistics of fluid force vary along the cylinder span considerably, indicating strong three dimensionality of the wake flows and their interaction.

Melting and flowing in multiphase environment

This paper presents a method to simulate the melting and flowing phenomena with different materials in multiple phases. In such a multiphase environment, solid objects are melted because of heating and the melted liquid flows while interacting with the ambient air flow. Our simulation is based on a modified lattice Boltzmann method (LBM), where the fluid dynamics of the air flow and the melted liquid is modeled within a common lattice framework. Therefore, no particular front tracking methods are required for the liquid–air interface. The liquid–solid and air–solid interfaces are implemented as curved boundaries in the LBM, which can accommodate arbitrarily shaped solid objects. Heat transfer is incorporated with a finite difference discretization of a standard diffusion–advection equation simulating the temperature evolution. The temperature and body forces (gravity and surface tension) are easily applied by adopting a new version of the LBM: multiple-relaxation-time LBM (MRTLBM). The melting and flowing behavior is controlled by the heat source, the viscosity and the body forces. All the numerical computations in our method are local and parallelizable, therefore, interactive speed is achieved by hardware acceleration on the contemporary graphics hardware (GPU).