Collisional Interactions in a Viscous Fluid

摘要本文研究的是流体动力学效应和碰撞相互作用都很重要的颗粒流动。这项研究介于悬浮流动和颗粒物质流动之间，涵盖了泥石流、泥浆和污泥输送、铣削和采矿应用、沉积物输送、磨料加工、抛光和表面侵蚀技术。这些流动的特点是具有密度相当的流体和固相，固体分数接近于充填床的固体分数，颗粒雷诺兹和斯托克斯数大于1。拟议的工作强调对碰撞相互作用的流体和固体力学的基本理解，包括模型和计算工具的开发，以及通过研究机会对学生和学者的教育。研究的重点是单个粒子与表面碰撞的相互作用。到目前为止，我们已经对正常的粒子碰撞进行了广泛的测量。这些结果表明，在临界斯托克斯数（约10）以下，在压缩润滑膜的过程中，所有颗粒的动能都损失了，颗粒没有反弹。在第二个斯托克斯数（约2000）以上，颗粒反弹，润滑层的影响可以忽略不计。提出的工作通过测量粒子可能滚动或滑动的倾斜碰撞来扩展这些实验。相关实验涉及液体中的双粒子碰撞，它与粒子-壁面碰撞不同，因为目标粒子在碰撞之前可能会移动。这两个实验将在斯托克斯数从10到3000之间进行，并包括不同的材料性能和表面条件。还提出了使用与粘性流体中的单个颗粒的受控碰撞来测量撞击过程中的表面变形和侵蚀。对于不同的斯托克斯数和材料性质，将检查正常和倾斜碰撞。一项分析研究将伴随测量。最后一个主题涉及由粒子碰撞引起的流体运动的探索性测量。当颗粒靠近壁面时，间隙中的流体被迫径向向外流动，然后当颗粒反弹时流体反过来。在单颗粒实验和致密颗粒流动中，这些流动逆转影响了壁面剪切应力。这项研究工作的一个组成部分是对学生和学者的教育。pi让学生参与他们研究的各个方面，包括撰写技术论文和在适当的科学会议上发言。在之前和正在进行的研究中，pi非常强调包括来自代表性不足的群体的学生和本科生的广泛参与。其中一些本科生因其杰出的研究而得到认可，大约一半的本科生继续攻读工程研究生课程。他们还通过社区和校园项目向当地学校展示了他们的研究成果。

COLLISIONAL INTERACTIONS IN A VISCOUS FLUID M.L. Hunt and C.E. Brennen Abstract The proposed work investigates particulate flows in which both hydrodynamic effects and collisional interactions are important. This research lies between suspension flows and granular material flows and encompasses debris flows, slurry and sludge transport, milling and mining applications, sediment transport, abrasive machining, polishing and surface erosion technologies. These flows are characterized by having fluid and solid phases of comparable density, solid fractions approaching that of a packed bed, and particle Reynolds and Stokes numbers greater than unity. The proposed work emphasizes a fundamental understanding of the fluid and solid mechanics of collisional interactions, including the development of models and computational tools, and the education of students and scholar through research opportunities. The research focuses on the interactions of individual particles colliding with a surface. To date, we have done extensive measurements of normal particle collisions. These results demonstrated that below a critical Stokes number, about 10, all of the particles kinetic energy is lost during the compression of the lubrication film with no rebound of the particle. Above a second Stokes number, about 2000, the particle rebounds with negligible effect of the lubrication layer. The proposed work expands on these experiments by measuring oblique collisions in which the particle may roll or slide. Related experiments involve binary-particle collisions in a liquid, which differs from the particle-wall collisions because the target particle may move prior to the impact. Both of these experiments would be performed for Stokes number from 10 to 3000, and include different material properties and surface conditions. Measurements are also proposed of the surface deformation and erosion during impact using controlled collisions with a single particle in a viscous fluid. Both normal and oblique collisions will be examined for different Stokes numbers and material properties. An analytical study will accompany the measurements. The final subject involves exploratory measurements of the fluid motion resulting from a particle collision. As a particle approaches a wall, the fluid in the gap is forced radially outward, and then the fluid reverses direction as the particle rebounds. These flow reversals affect the wall shear stress in the single particle experiments and in dense particulate flows. An integral part of this research work is the education students and scholars. The PIs have included students in all aspects of their research, including the authoring of technical papers and presentations at appropriate scientific meetings. In prior and ongoing research, the PIs have placed a heavy emphasis on the inclusion of student from underrepresented groups and extensive involvement of undergraduate students. Some of these undergraduates have been recognized for their outstanding research, and approximately half have gone on to engineering graduate programs. The PIs have also presented their research to local schools through community and campus programs.