Rod Dynamics in Turbulence: Simultaneous 3D measurements of Anisotropic Particles and Velocity Fields

Wesleyan University, Middletown CT

Investigators

Abstract

****Technical Abstract**** In a wide range of natural and industrial situations, turbulent flows carry particulate material. As such, the dynamics of turbulent suspensions and aerosols has been an active area of research. Significant progress has been made in characterizing the motion of spherical particles in turbulence; much less is known, however, about the dynamics of anisotropic particles. The rotation of anisotropic particles is determined by small scale properties of turbulence that are nearly universal across a wide range of flows, and so anisotropic particles provide a rich system where experiments can be directly compared with theory and simulations. The research proposed here will provide the first high-resolution experimental measurements of the 3D dynamics of rod shaped particles in turbulence. We will then extend these measurements to anisotropic objects across the full range of aspect ratios from rods to isotropic particles to disks. We will also implement a recently developed measurement system that will allow extremely high seeding densities necessary to measure the velocity gradients of the flow simultaneously with measurements of rod motion. This will allow measurement of the stretching experienced by the particle along its trajectory which is the fundamental quantity responsible for preferential alignment of anisotropic particles. Education and research training are central to this project, which will support the mentoring of undergraduates, graduate students, and a postdoctoral scientist, as well as training K-12 educators in physical science. ****Non-Technical Abstract**** In a wide range of natural and industrial situations, turbulent flows carry particulate material. For example, clouds are turbulent flows containing water droplets and ice crystals. Papermaking uses turbulent suspensions of fibers. If the particles are spheres, there are a variety of tools available for measuring their motion. But usually the particles are not spheres, and the movement and rotations of non-spherical particles have never before been measured as they are carried by a turbulent flow. This project will develop experimental tools to make these measurements. Particle rotations are of particular interest because their statistics are expected to be similar in all turbulent flows, and measurements can be compared with theoretical predictions for the universal properties of turbulence. This work seeks to establish a clear understanding of the fundamental characteristics of non-spherical particle motion in laboratory turbulent flows that can be used to understand more complex applications such as icy clouds and papermaking. Education and research training are central to this project, which will support the mentoring of undergraduates, graduate students, and a postdoctoral scientist, as well as training K-12 educators in physical science.