Model of turbulence penetration into a suspension layer on a sediment bed and effect on vertical solute transfer
Model of turbulence penetration into a suspension layer on a sediment bed and effect on vertical solute transfer
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DOI：
10.1007/s10652-012-9241-8
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发表时间：
2012-10-01
影响因子：
2.2
通讯作者：
Stefan, Heinz G.
中科院分区：
文献类型：
--
作者：
Higashino, Makoto;Stefan, Heinz G.
本文研究了悬浮沉积物层（如湖泊、水库或河口底部）中由上方速度脉动传播引起的垂直扩散物质（溶质）迁移。模拟了悬浮层中速度波动的衰减及其对溶质通过悬浮层传递的影响。为了模拟高浓度悬沙层上的大涡向下游运动，沿悬沙层上边界沿着施加一个向下游运动的速度脉动。速度波动和下游速度由悬浮层顶部的剪切速度（U-*）归一化。悬浮层内的流向和垂向速度分量由二维连续性和Navier-Stokes方程得到。湍流与深度的持久性，因为它从上覆水渗透到悬浮层，被发现取决于其振幅，其周期，和悬浮液的表观粘度。当湍流频率较低时，湍流可以有效地传播到悬浮液层中，悬浮液的表观粘度较高。垂直传质的影响参数的穿透深度和有效扩散系数，并与悬浮液的表观粘度，施密特数和剪切速度的悬浮层顶部。粘性对湍流穿透的增强作用类似于振荡平板附近的流动（Stokes第二问题），但与湍流穿透静止多孔和可渗透的沉积物床相反。这些信息适用于湖泊、河流蓄水池和河口的沉积物/水界面的水质建模。
The vertical diffusional mass (solute) transfer through a suspended sediment layer, e.g. at the bottom of a lake, reservoir or estuary, by the propagation of velocity fluctuations from above was investigated. The attenuation of the velocity fluctuations in the suspension layer and the associated effect on solute transfer through the suspension layer was simulated. To represent large eddies traveling downstream in water over a high-concentration suspended sediment layer, a streamwise velocity fluctuation moving in downstream direction was imposed along the upper boundary of the suspension layer. Velocity fluctuations and downstream velocity were normalized by the shearvelocity (U-*) at the top of the suspension layer. Streamwise and vertical velocity components inside the suspension layer, were obtained from the 2-D continuity and the Navier-Stokes equations. The persistence of turbulence with depth-as it penetrates from the overlying water into the suspension layer-was found to depend on its amplitude, its period, and on the apparent viscosity of the suspension. The turbulence was found to propagate efficiently into the suspension layer when its frequency is low, and the apparent viscosity of the suspension is high. Effects on vertical mass transfer were parameterized by penetration depth and effective diffusion coefficient, and related to apparent viscosity of the suspension, Schmidt number and shear velocity on top of the suspension layer. The enhancement of turbulence penetration by viscosity is similar to the flow near an oscillating flat plate (Stokes' second problem), but is opposite to turbulence penetration into a stationary porous and permeable sediment bed. The information is applicable to water quality modeling mear the sediment/water interface of lakes, river impoundments and estuaries.