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）资助。0854230孔雀，托马斯的PI发现了一个显着的新的推进机制，在密度分层的环境中运行。其基本机制是一个很少被研究的现象，扩散驱动流，首先在岩石裂缝和海洋边界混合的盐运输的背景下确定;尽管它的起源可以追溯到普朗特的热成风研究。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则而不是例外。如果一个漂浮物是不对称的，扩散驱动的水流会产生一个不平衡的力来推动它。PI已经在盐分层的水中证明了这个概念，使用了精心设计的三角形楔形物。乍一看，这种效应是非常违反直觉的，不需要任何运动部件，因此似乎从任何地方产生推进力;而事实上，运动的动能来自潜在的分子扩散过程。许多基本问题仍有待回答，包括：推进速度如何与控制参数成比例？层结对垂直流体运动的抑制是否意味着封闭总是一种影响？这种效应是否被利用来在自然环境中（如湖泊和海洋）传输颗粒和生物体？这项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方案上，旨在研究无量纲组的相互依赖性，这些无量纲组控制着推进速度，受到三维度、形状、分层、扩散率、粘度和惯性的影响。计划中的粒子图像测速技术（PIV）对这种小尺度、低速流动的测量是困难的。这些数据将揭示底层的流动结构，以帮助开发分析和数值模型。本科研究生将通过麻省理工学院UROP项目和麻省理工学院埃杰顿实验室与Jim Bales博士协调的流动可视化研究项目参与实验。可视化将被张贴到流体力学的知识库，测试分层流的数值模拟的基准数据将被张贴在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.