明渠湍流边界层中颗粒的运动与分布

利用直接数值模拟、点球浸入边界法和颗粒离散元法相结合的方法, 模拟了颗粒在明渠湍流边界层中的运动, 并对颗粒的瞬时位置进行了Voronoi 分析, 定量研究了颗粒在湍流边界层中的运动和分布规律. 研究发现:颗粒的输运对湍流的统计特征有影响, 其运动与近壁区湍流拟序结构密切相关, 在"喷发"结构作用下被带离壁面, 在"扫掠" 结构和自身重力作用下回到壁面; 在湍流边界层中, 颗粒倾向于聚集在低流速带, 呈条带状分布;颗粒在大部分时间处于"簇"状态, 偶尔跳跃到"空" 状态, 但能够很快回到邻近低速区域. 

DISTRIBUTION AND MOTION OF PARTICLES IN THE TURBULENT BOUNDARY LAYER OF CHANNEL FLOW

This paper numerically investigates particles immersed in the turbulent boundary layer of channel flow. The methodology is a combination of three cutting-edge numerical technologies, i.e., the direct numerical simulation of turbulent flow, the point-particle immersed boundary method and the discrete particle method. We quantify the motion and distribution of near-wall particles by means of Voronoi analysis based on a set of instantaneous particle positions. It was found that the motion of particles have strong effects on flow velocity profiles and turbulence intensities, is closely related to the dynamics of the near wall coherent flow structures, i.e., the ejections of low-speed fluid carry particles towards the outer flow and the sweeps of high-speed fluid as well as gravitational settling bring particles back towards the wall. Most of particles in the turbulent boundary layer reside preferentially in low speed fluid regions and streamwise-aligned streaky structures. Particles keep in "clusters" over substantial time scales and sometimes they jump into "voids", after which those particles relatively quickly migrate back to a neighbouring low speed region.