Turbulence-Resolving Numerical Study of Hyperpycnal Plumes
Date Issued
2014
Date
2014
Author(s)
Chen, Saint-Yao
Abstract
In the present study, large eddy simulation (LES) is employed to study the behavior of the hyperpycnal plume under different bottom slope conditions. The bottom slopes of 0.005 and 0.01 are chosen. In order to understand the dynamics of the undercurrent in regions of the plunging point, main body, and front point, the results are divided into two parts for the discussion.
First, we estimate the entrainment coefficient of the ambient fluid and the Froude number to investigate the dynamic behavior between the hyperpycnal plume and their surroundings. Both of the gentle and steep cases show that the entrainment of the ambient fluid occurs near the plunging region. The interfacial drag increases as the slope increases, which results in high entrainment coefficients on the steep slope. The entrainment coefficient of the gentle slope in the front region shows that considerable mass of the hyperpycnal plume is detrained into the ambient fluid, while the steep case indicates that the ambient fluid is entrained into the hyperpycnal plume.
Second, the vertical distribution of the mean velocity, the sediment concentration, and the density field are investigated. The results indicate that the mean velocity of the steep slope is higher than that of the gentle slope, which is because the downslope gravitational force increases as the slope increases. Moreover, lower sediment concentration in the front region indicates occurrence of mixing. The TKE budget analysis shows that turbulence is mainly generated at the interface between the clear-water and sediment-containing layer. Additionally, the strong downward velocity in the plunging region explains why the entrainment of the ambient fluid occurs. Furthermore, comparison of the run-out distance between two different bottom slopes shows that the steep slope generates larger downslope gravitational force that drives a longer run-out distance.
Subjects
含沙異重流
大渦流模式
捲水係數
福祿數
紊流能量收支平衡
Type
thesis
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