MRT-LBM三重网格局部加密算法研究

应用MRT-LBM计算流场中运动粒子上的力和力矩时，可使用三重网格局部加密方法来提高计算结果的精度.将流场计算区域划分为互不重合的粗糙区、过渡区和加密区，相邻区域界面重合节点上的物理参数如密度、速度和应力等保持连续，不同区域的分布函数通过过渡区边界点进行传递，运算程序采用碰撞-迁移算法，给出了数据的初始化过程和加密的网格结构.通过对含非对称放置的粒子Couette流动，分别采用标准Boltzmann、全场加密、局部二重加密和三重加密的4种网格进行计算.数值计算结果表明，三重网格加密算法减少了计算结果的波动.对方腔流顶盖下方左右奇异角落处应用三重局部网格加密，结果显示，对雷诺数1 000的方腔流动，沿腔中心线的速度分布与经典文献结果对比效果良好，压力轮廓图的噪声明显降低，应力振荡明显减少.模拟结果证实了所建立的局部加密方法的有效性. 

Research on Three-Block Local Grid Refinement Method in MRT-LBM

To improve the computational accuracy of hydrodynamic force and torque for a moving particle in viscous flow,a three-block local grid refinement method was proposed based on the multi-relaxation-time (MRT)lattice Boltzmann method (LBM).Firstly,the flow field was divided into three blocks comprising coarse,buffer and cage domain.The dynamic physical parameters,such as density,velocity and stress of the superposition nodes,were considered to be continuous at the interface between every two blocks,the distribution functions of different blocks were developed to be transferred at every block buffer layer.Then pre-collision sub-step implementation was employed to initialize the physical value for the new domain grid points,and to construct the three domain structures.Finally,calculations were implemented based on the standard Boltzmann,full-domain refinement,two-block and three-block local grid refinement four methods respectively for the Couette flow with an asymmetrical placed particle.Simulation results show that,the level of dynamic fluctuation with the three-block grid refinement method is significantly suppressed.And for a lid-driven cavity flow,two singular corners under the lid refined with three-block meshes,Reynolds number 1000 flow,the calculation result shows the velocity distribution along mid-plane of the cavity is agree well with benchmark's results,and the noise on the pressure contour is significant reduced and stress oscillations evidently get down.All results prove that the present method is effective to high resolution computation with LBM.