Propulsion through Diffusion

该奖项是根据2009年美国复苏和再投资法案（公法111-5）.0854230资助的pi发现了一种在密度分层环境中运行的非凡的新推进机制。潜在的机制是一种很少被研究的现象，即扩散驱动流动，首先在岩石裂缝中的盐运输和海洋边界混合的背景下确定；尽管它的起源可以追溯到普朗特尔对热风的研究。扩散驱动的流动是由于扩散和重力在倾斜表面上的相互作用而自发产生的，这对于漂浮的中性浮力物体来说是规律而不是例外。如果一个漂浮物是不对称的，扩散驱动的流动就会产生一种不平衡的力来推动它。pi使用精心设计的三角形楔块在盐层水中演示了这一概念。乍一看，这种效果是非常违反直觉的，它不需要任何移动部件，因此似乎凭空产生了推进力；而事实上，运动的动能是从潜在的分子扩散过程中获得的。许多基本问题仍有待解决，包括：推进速度如何与控制参数成比例？分层对垂直流体运动的抑制是否表明约束总是有影响？在湖泊和海洋等自然环境中，这种效应是否被用于传输粒子和生物体？本研究将发展对流体动力学中一种新的物理效应的理解：通过扩散推进。计划中的研究集中在一个精心协调的实验室实验项目上，旨在调查受三维、形状、分层、扩散、粘度和惯性影响的控制推进速度的无量纲群的相互依赖性。计划中的粒子图像测速（PIV）对于这种小尺度、低速流动来说是困难的。这些数据将揭示潜在的流结构，以帮助开发分析和数值模型。本科生将通过麻省理工学院UROP项目和与麻省理工学院Edgerton实验室的Jim Bales博士协调的流动可视化研究项目参与实验。可视化结果将被发布到流体力学知识库中，测试分层流动数值模拟的基准数据将被发布到PI的网站上。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).0854230 Peacock, Thomas The PIs have discovered a remarkable new propulsion mechanisms that operates in density-stratified environments. The underlying mechanism is a little-studied phenomenon, diffusion-driven flow, first identified within the context of salt transport in rock fissures and ocean boundary-mixing; although its origins date back to Prandtl's study of thermal winds. Diffusion-driven flow spontaneously arises due to an interaction between diffusion and gravity on sloping surfaces, which are the rule rather than the exception for floating, neutrally-buoyant objects. If a floating object is asymmetric, diffusion-driven flow produces an unbalanced force that propels it. The PIs have demonstrated this concept in salt-stratified water, using a carefully designed triangular wedge. At first sight, the effect is highly counterintuitive, requiring no moving parts and therefore seemingly generating propulsion from nowhere; when in fact, the kinetic energy of motion is drawn from the underlying molecular diffusion process. Many fundamental questions remain to be answered, including: How does the propulsion speed scale with the governing parameters? Does suppression of vertical fluid motion by stratification dictate that confinement is always an influence? And is this effect exploited to transport particles and organisms in natural settings, such as lakes and oceans? This study will develop understanding of a new physical effect in fluid dynamics: propulsion through diffusion. The planned studies center on a carefully coordinated program of laboratory experiments, designed to investigate the interdependency of the dimensionless groups that govern the propulsion speed as affected by, three-dimensionality, shape, stratification, diffusivity, viscosity and inertia.. The planned Particle Image Velocimetry (PIV) is difficult for such small-scale, low-speed flows. This data will reveal the underlying flow structure, to help develop analytical and numerical models. Undergraduate research students will be involved in the experiments through the MIT UROP program and through a flow-visualization research project coordinated with Dr. Jim Bales at the MIT Edgerton Lab. Visualizations will be posted to repositories of fluid mechanics, and benchmark data for testing numerical simulations of stratified flow will be posted on the PI's website.