Particle-laden flow down a slope in uniform stratification
Particle-laden flow down a slope in uniform stratification
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DOI：
10.1017/jfm.2014.413
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发表时间：
2014-08
影响因子：
3.7
通讯作者：
K. Snow;B. Sutherland
中科院分区：
文献类型：
--
作者：
K. Snow;B. Sutherland
摘要进行了释放锁的实验室实验，以考察沿斜坡向下进入恒定密度和线性分层大气中的含盐量和颗粒的流动。研究了低空(表面传播)流和高空(浑浊)流，重点讨论了环境层结对浑浊流的影响。测量的是沿坡面的锋面速度和浊流从坡面分离并侵入环境的深度。将这些结果与用斜率来描述流动演变和分离深度的理论的预测进行了比较，该理论以斜率来描述流动演变和分离深度，其中夹带参数$E$(夹带与流速的比率)为S，相对层化参数S(环境密度差与相对电流密度之比)和一个新参数(定义为颗粒沉降与卷吸速度之比)。在考虑小分离深度和大分离深度限制的情况下，显式地给出了分离深度的隐式预测公式H_S。在“弱”浑浊流的前一种情况下，卷吸和颗粒沉降并不重要，当周围流体的密度等于船闸内流体的密度时，就会发生分离。在后一种情况下，浊流很强，夹带和颗粒沉降对分离深度有重要影响。与理论一致，我们发现，如果颗粒尺寸(从而沉降率)足够大，并且如果电流在从斜坡分离之前传播许多锁定长度，则分离深度确实取决于$\Gamma$。结合弱浊流和强浊流分离深度的显式组合预测，在较宽的参数范围内与实验测量符合得很好。
Abstract Lock–release laboratory experiments are performed to examine saline and particle-laden flows down a slope into both constant-density and linearly stratified ambients. Both hypopycnal (surface-propagating) currents and hyperpycnal (turbidity) currents are examined, with the focus being upon the influence of ambient stratification on turbidity currents. Measurements are made of the along-slope front speed and the depth at which the turbidity current separates from the slope and intrudes into the ambient. These results are compared to the predictions of a theory that characterizes the flow evolution and separation depth in terms of the slope $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}s$ , the entrainment parameter $E$ (the ratio of entrainment to flow speed), the relative stratification parameter $S$ (the ratio of the ambient density difference to the relative current density) and a new parameter $\gamma $ defined to be the ratio of the particle settling to entrainment speed. The implicit prediction for the separation depth, $H_s$ , is made explicit by considering limits of small and large separation depth. In the former case of a ‘weak’ turbidity current, entrainment and particle settling are unimportant and separation occurs where the density of the ambient fluid equals the density of the fluid in the lock. In the latter case of a ‘strong’ turbidity current, entrainment and particle settling crucially affect the separation depth. Consistent with theory, we find that the separation depth indeed depends on $\gamma $ if the particle size (and hence settling rate) is sufficiently large and if the current propagates many lock lengths before separating from the slope. A composite prediction that combines the explicit formulae for the separation depth for weak and strong turbidity currents agrees well with experimental measurements over a wide parameter range.