Interaction between an inclined gravity current and a pycnocline in a two-layer stratification
Interaction between an inclined gravity current and a pycnocline in a two-layer stratification
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DOI：
10.1017/jfm.2020.9
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发表时间：
2020-01
影响因子：
3.7
通讯作者：
Y. Tanimoto;N. Ouellette;J. Koseff
中科院分区：
文献类型：
--
作者：
Y. Tanimoto;N. Ouellette;J. Koseff
通过一系列室内实验，研究了重力流沿斜坡向下进入静止两层分层的特性。密度跃层的存在导致重力流分裂并侵入到环境中的两个不同水平的中性浮力，而不是在分层介质中的重力流的经典描述是一个纯粹的底流或interflow。分裂行为被观察到依赖于理查森数（$Ri_{\unicode[STIX]{x1 D 70 C}}$）的重力流，制定为过剩密度和环境分层的比率。对于低$Ri_{\unicode[STIX]{x1 D 70 C}}$，下溢更占主导地位，而在高$Ri_{\unicode[STIX]{x1 D 70 C}}$ interflow更占主导地位。然而，随着$Ri_{\unicode[STIX]{x1 D 70 C}}$的增加，我们发现分裂行为最终变得与$Ri_{\unicode[STIX]{x1 D 70 C}}$无关。此外，我们还确定了两种不同类型的波，在密度跃层上形成的重力流的入侵。底流为主的政权导致密度跃层位移的波峰的速度被锁定的重力流，而interflow为主的政权推出的内波，移动速度比重力流头或界面侵入快得多。
A series of laboratory experiments were conducted to investigate the characteristics of a dense gravity current flowing down an inclined slope into a quiescent two-layer stratification. The presence of the pycnocline causes the gravity current to split and intrude into the ambient at two distinct levels of neutral buoyancy, as opposed to the classical description of gravity currents in stratified media as being either a pure underflow or interflow. The splitting behaviour is observed to be dependent on the Richardson number ($Ri_{\unicode[STIX]{x1D70C}}$) of the gravity current, formulated as the ratio of the excess density and the ambient stratification. For low $Ri_{\unicode[STIX]{x1D70C}}$, underflow is more dominant, while at higher $Ri_{\unicode[STIX]{x1D70C}}$ interflow is more dominant. As $Ri_{\unicode[STIX]{x1D70C}}$ increases, however, we find that the splitting behaviour eventually becomes independent of $Ri_{\unicode[STIX]{x1D70C}}$. Additionally, we have also identified two different types of waves that form on the pycnocline in response to the intrusion of the gravity current. An underflow-dominated regime causes a pycnocline displacement where the speed of the wave crest is locked to the gravity current, whereas an interflow-dominated regime launches an internal wave that moves much faster than the gravity current head or interfacial intrusion.