明渠中有机质微粒沉降过程的随机游走模拟

基于明渠流动的主要特点，考虑紊动强度的垂向非均匀性，及颗粒运动的游荡效应（loitering effect）影响，对微粒运动基本方程进行改进，建立了明渠非均匀紊流中考虑游荡效应的随机游走模型，对明渠中微粒的沉降损失进行了模拟分析.模拟结果显示，不考虑游荡效应影响时，明渠中微粒的沉降损失率可用微粒沉速与水深之比计算；而在游荡效应影响下，微粒沉降损失率会发生约18%~27%的下降，下降百分比与均匀紊流中微粒沉速在游荡效应影响下的折减百分比渐近值（19~25%）基本一致.本文结论基于不考虑微粒重悬浮、游荡效应为紊流对微粒沉降的主导影响机理等前提，主要适用于对明渠中细小有机质微粒沉降至床底过程更准确的计算分析.

Random walk simulation of organic particle sedimentation process in the open channels

Based on the main characteristics of open channel flows, this research built a random walk model for fine particles within the inhomogeneous open channel turbulence, with modifications concerning influences of the vertical inhomogeneity of turbulence intensity and loitering effect. Using the established model, the sedimentation loss of fine particles in the open channels was simulated. Simulation results showed that, when influence of the loitering effect was not considered, particle sedimentation loss rate could be calculated by the ratio of particle settling velocity to the water depth; when influence of the loitering effect was considered, particle sedimentation loss rate would have a 18%~27% reduction compared to quiescent environments. The reduction percentage was basically consistent with the asymptotic value of declining percentage of particle settling velocity (19%~25%) in the homogeneous turbulent fields. The conclusion of this article was mainly based on two premises that the resuspension of particle was not considered, and the loitering effect was the dominant mechanism of turbulence on particle settling. Proposed method and results can be applied to calculate the sedimentation process of particles to the channel bottom more accurately.