Collaborative Research: Double-diffusive sedimentation

本项目将采用理论、数值模拟和实验相结合的方法研究分层液体系统中不稳定性引起的运动。例如，当河流中的淡水进入海洋时，沉积物和盐的浓度梯度同时形成。在理论上可以预测的某些条件下，这些梯度的存在会导致不稳定的情况，从而引起含沙水的对流运动。初步结果表明，这种运动强烈影响沉积物的沉降速度和输运。该项目将开发一个框架，用于分析在河口的各种情况下由这种不稳定性引起的运动。然而，该框架将更广泛地适用于环境、地球物理、天体物理和工程流程中的问题。这个合作项目将使用理论、计算和实验工具来探索双扩散沉积在广泛条件下的线性和非线性动力学。线性稳定性理论、直接数值模拟和实验室实验将进行四种基本配置：a)咸水之上的含沙淡水层；B)咸水下面一层富含沉积物的淡水；C)线性浓度梯度，沉积物分层不稳定；D)线性浓度梯度，沉积物稳定分层。水的剪切流的影响，这是适合河口，将包括在内。该研究将解决在这些系统中观察到的一系列有趣现象，包括指法不稳定性、水平侵入和颗粒系统中形成的楼梯。拟议的研究将确定在各种参数制度下的主要不稳定机制，并将在每种情况下为双扩散沉降提供定量的标度定律。

CBET 1438052/1437275This project will use theory, numerical simulation, and experiments to study the motion that is induced by instabilities in stratified liquid systems. For example, when fresh water from a river enters the ocean, concentration gradients of sediment and salt form simultaneously. Under certain conditions that can be predicted theoretically, the presence of these gradients leads to an unstable situation that induces convective motion of the sediment-laden water. Preliminary results show that this motion strongly affects the settling velocity and transport of the sediment. This project will develop a framework for analyzing motions induced by such instabilities in a variety of situations pertaining to river estuaries. However, the framework will be more broadly applicable to problems in environmental, geophysical, astrophysical, and engineering flows. This collaborative project will use theoretical, computational, and experimental tools to explore the linear and nonlinear dynamics of double diffusive sedimentation under a wide range of conditions. Linear stability theory, direct numerical simulation, and laboratory experiments will be conducted for four basic configurations: a) a layer of sediment-laden fresh water above saline water; b) a layer of sediment-laden fresh water below saline water; c) linear concentration gradients with sediment being unstably stratified; d) linear concentration gradients with sediment being stably stratified. Effects of shear flow in the water, which is appropriate for river estuaries, will be included. The research will address a range of interesting phenomena observed in these systems including fingering instabilities, horizontal intrusions, and staircases formed in particulate systems. The proposed research will identify dominant instability mechanisms in various parameter regimes, and will provide quantitative scaling laws for double diffusive sedimentation in each case.