Two timescales for longitudinal dispersion in a laminar open-channel flow

• Published in: Journal of hydrodynamics. Series B Vol. 29; no. 6; pp. 1081 - 1084
• Main Author: 王宇飞;槐文信;杨中华;季斌
• Format: Journal Article
• Language: English
• Published: Singapore Elsevier Ltd 01.12.2017; Springer Singapore; State Key Laboratory of Water Resources and Hydropower Engineering Science, Wuhan University, Wuhan 430072, China
• Subjects: Early stage; Engineering; Engineering Fluid Dynamics; Hydrology/Water Resources; Letter; longitudinal dispersion; Numerical and Computational Physics; random walk particle method; scalar transport; Simulation; 分散系数;隧道;Gaussian;流动;平均数;试验性;尺寸;分发; Early stage; longitudinal dispersion; scalar transport; random walk particle method
• ISSN: 1001-6058; 1878-0342
• DOI: 10.1016/S1001-6058(16)60821-1

At small dimensionless timescales T（= tD/H^2）, where t is the time, H is the depth of the channel and D is the molecular diffusion coefficient, the mean transverse concentration along the longitudinal direction is not in a Gaussian distribution and the transverse concentration distribution is nonuniform. However, previous studies found different dimensionless timescales in the early stage, which is not verified experimentally due to the demanding experimental requirements. In this letter, a stochastic method is employed to simulate the early stage of the longitudinal transport when the Peclet number is large. It is shown that the timescale for the transverse distribution to approach uniformity is T= 0.5, which is also the timescale for the dimensionless temporal longitudinal dispersion coefficient to reach its asymptotic value, the timescale for the longitudinal distribution to approach a Gaussian distribution is T= 1.0, which is also the timescale for the dimensionless history mean longitudinal dispersion coefficient to reach its asymptotic value.