A novel mixing mechanism in sinuous seafloor channels: Implications for submarine channel evolution
A novel mixing mechanism in sinuous seafloor channels: Implications for submarine channel evolution
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DOI：
10.1016/j.geomorph.2017.11.008
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发表时间：
2018-02-15
期刊：
影响因子：
3.9
通讯作者：
Keevil, G. M.
中科院分区：
文献类型：
--
作者：
Dorrell, R. M.;Peakall, J.;Keevil, G. M.
以往对蜿蜒海底河道中密度流的实验研究几乎都是通过考虑与时间无关的瞬时流量测量，或者通过汇编时间平均流量测量来研究流体动力学的。在此，我们对一个由恒定流量源供给的蜿蜒河道中密度驱动流的随时间变化的动力学进行了一项新的研究。实验表明，虽然源条件在时间上可能是稳定的，但流动条件在时间上是不稳定的，流动变化的时间尺度是由流动与河道地形的相互作用所驱动的。时间变化显示，顺流和横流的流动情况与时间平均观测值和预测值有显著差异，其差异的尺度大于等效直河道中湍流所预测的尺度。研究表明，大尺度变化会增加整个水流高度上湍流的平均产生量，为重力流中泥沙的增强混合提供了一种新机制。此外，近底二次流方向的变化记录了流动条件的这种大尺度变化，为减少推移质的横向输运以及解释蜿蜒海底河道系统的最终稳定提供了一种合理的机制。（C）2017爱思唯尔有限公司。保留所有权利。
Previous experimental studies of density currents in sinuous seafloor channels have almost exclusively studied hydrodynamics either by considering time independent, instantaneous, flow measurements or by compiling time-averaged flow measurements. Here we present a novel study of the time dependent dynamics of a density driven flow in a sinuous channel fed by a source of constant discharge. The experiments show that whilst source conditions may be temporally steady, flow conditions are temporally unsteady with timescales of flow variation driven by flow interaction with channel topography. Temporal variations reveal that both downstream and cross-stream flows vary significantly from time average observations and predictions, across scales larger than those predicted for turbulence in equivalent straight channels. Large-scale variations are shown to increase the average production of turbulence across the height of the flow, providing a new mechanism for enhanced mixing of sediment within gravity currents. Further such large-scale variations in flow conditions are recorded in the change in orientation of near-bed secondary flow, providing a plausible mechanism to reduce the cross-stream transport of bedload material and explain the ultimate stabilisation of sinuous seafloor channel systems. (C) 2017 Elsevier B.V. All rights reserved.