Using shape to control the orientations and positions of particles in processing flows

主要研究者：Koch，Donald L.提案编号：1435013机构：康奈尔大学题目：利用形状控制加工流程中颗粒的方向和位置最近在制造具有受控形状的颗粒方面的进展促进了人们对可以从这种颗粒的组装中产生的材料范围的兴奋。 虽然注意力主要集中在形状对颗粒由于随机热运动而聚集的方式的影响上，但形状也可以对流体流动引起的结构产生令人惊讶的后果。 直到最近，人们一直认为所有轴对称的刚性粒子在粘性流体的剪切流中连续旋转。 然而，研究人员最近预测存在一类具有尖锐外缘的非旋转环形颗粒。 这个项目将包括计算和理论技术的应用，以扩大流动排列颗粒形状的范围，并探索其实用性。 一个实验项目将探索制造颗粒的方法，并观察它们的流动取向行为。 基础研究将由具有特定机械，流变或渗透性能的材料的各种目标应用指导。 参与研究的学生将被鼓励作为发明家-科学家探索这些应用。 本科研究人员将协助混沌动力学的理论研究和制造方法的发展。 这项研究的视觉吸引力将在当地儿童的K-12外展活动中得到利用？在低雷诺数简单剪切流中排列的刚性颗粒的行为将使用边界元法（BEM）计算和细长体理论分析来探索。边界元法模拟将用于：（1）寻找在中等展弦比下最有效地停止旋转的横截面形状;（2）探索具有填充中心（以提供气体屏障）的环可以流动对齐的可能性;以及（3）显示具有内外和前后不对称性的环在其流动对齐状态下表现出稳定的横向流线漂移。 细长体理论（SBT）将被开发为一个大的环直径与厚度的比率的环。 该SBT的一个新颖方面是需要确定由环横截面附近的速度梯度引起的每单位圆周的力。 这个交叉项没有出现在以前的SBT的颗粒与圆形或椭圆形的横截面。 SBT模拟将确定是否可以通过与其他环的流体动力学相互作用来诱导流动对准环翻转，并确定具有横流漂移的颗粒在接近壁时达到的平衡位置。 SBT计算也将被用来探索的可能性，从轴对称的轻微偏差可能会导致粒子，经历混乱的旋转和平移运动在一个简单的剪切流，导致自分散行为的布朗运动或粒子-粒子相互作用的情况下。 非前后对称环，流动对齐，并表现出交叉流漂移将使用光刻制造。 为了产生前后对称的环，这些环与流体运动对齐但平移，研究人员将探索一种混合合成方法，该方法基于在微流体液滴过程中产生环形颗粒，随后将颗粒嵌入薄膜中并拉伸以产生环的尖锐外缘。 粒子的三维平移和旋转运动将在反向旋转的库埃特装置中观察到。 将测量稀悬浮液和半稀悬浮液的流变学，以揭示由于流动对齐而导致的粘度降低。

PI: Koch, Donald L.Proposal Number: 1435013Institution: Cornell UniversityTitle: Using shape to control the orientations and positions of particles in processing flowsRecent advances in the ease of fabricating particles with controlled shape have fostered excitement about the range of materials that can be created from assemblies of such particles. While attention has focused primarily on the influence of shape on the manner in which particles assemble due to random thermal motion, shape can also have surprising consequences for structure induced by fluid flows. Until recently, it had been thought that all axisymmetric, rigid particles rotated continuously in shear flows of viscous fluids. However, the investigators recently predicted the existence of a class of non-rotating ring-shaped particles with sharp outer edges. This project will include the application of computational and theoretical techniques to expand the range of flow-aligning particle shapes and explore their utility. An experimental program will explore methods to fabricate the particles and observe their flow aligning behavior. The fundamental studies will be guided by various target applications for materials with specific mechanical, rheological or permeability properties. The students involved in the research will be encouraged to explore these applications as inventor-scientists. Undergraduate researchers will aid with theoretical studies of chaotic dynamics and with the development of fabrication methods. The visually appealing nature of the research will be exploited in K-12 outreach activities at a local children?s science museum, the Ithaca Sciencenter.The behavior of rigid particles that align in a low Reynolds number simple shear flow will be explored using boundary element method (BEM) computations and slender-body theory analysis. BEM simulations will be used to: (1) Search for cross-sectional shapes that are most effective in stopping rotation at moderate aspect ratios; (2) Explore the possibility that a ring with a filled center (to impart a gas barrier) can flow align; and (3) Show that rings with both in-out and fore-aft asymmetry exhibit a steady cross-streamline drift in their flow-aligned state. Slender-body theory (SBT) will be developed for rings with a large ratio of ring diameter to thickness. A novel aspect of this SBT is the need to determine the force per unit circumference induced by the velocity gradient near the ring cross-section. This cross term has not appeared in previous SBT for particles with circular or elliptical cross-sections. SBT simulations will determine whether flow-aligning rings can be induced to flip by hydrodynamic interactions with other rings and to determine the equilibrium position a particle with cross-stream drift reaches as it approaches a wall. SBT calculations will also be used to explore the possibility that slight deviations from axisymmetry can lead to particles that undergo chaotic rotational and translational motions in a simple shear flow, leading to a self-dispersive behavior in the absence of Brownian motion or particle-particle interactions. Non-fore-aft symmetric rings that flow-align and exhibit cross-stream drift will be fabricated using photolithography. To produce fore-aft symmetric rings that align but translate with the fluid motion, the investigators will explore a hybrid synthesis based on producing toroidal particles in a microfluidic drop process and subsequently embedding the particles in a film and stretching to create the sharp outer edge of the ring. The three-dimensional translational and rotational motion of the particles will be observed in a counter-rotating Couette device. The rheology of dilute and semi-dilute suspensions will be measured to reveal the decrease in viscosity due to flow alignment.