Effects of particle shape and fluid shear on the kinematics and mass transfer of large particles in turbulent flow

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PI: Variano, EvanProposal Number: 1604026The goal of the proposed research is to experimentally and theoretically explore the physics of turbulent flows with high concentration of particles. The proposal focuses on the complex, and at the same time common in engineering applications, case of non-spherical particles that move on the flow field because of the combined effectws of drift and of inertia. Such flows are prominent in the chemical process industry (e.g., fluidized bed catalytic reactors, pneumatic transport) and in the environment. Particles large enough to exceed the Stokesian limit will be measured in turbulent flow. The general objective is to better understand particle motion for cases in which inertia is non-negligible, and the specific objective is to understand how particle shape influences response to fluid shear. Laboratory measurements will reveal particle acceleration, rotation, and mass transfer between individual particles and the surrounding fluid. One group of particles will be manufactured with transparent, refractive-index-matched materials and internal tracers, thereby enabling optical measurements of their rotation and translation in three dimensions. A second group of particles will fabricated from a new type of neutrally-buoyant silica-sucrose glass that was designed to slowly dissolve, thereby enabling measurements of the mass exchange between particles and fluid. The shapes that will be studied are cylinders and cones; additional shape features resembling tails and fins will be added to help evaluate the role of particle alignment with local coherent structures in the turbulent flow. Extending beyond the Stokesian limit can reveal new phenomena because inertia adds complexity to the interaction of particles with local shear. The proposed project will explore the inertial regime, providing observational evidence of how large particles interact with turbulence. Numerical methods cannot easily simulate the motions of interest, and thus the proposed laboratory techniques were developed to rapidly explore a large range of shapes. Particles of the type examined herein appear in many areas of science and engineering, and the proposed work will advance study in these areas by providing the first detailed description of the relevant physics. An example engineering opportunity lies in the design of small-scale robotic vehicles. The results herein will enable the design of navigation and sensing strategies, and determine how vehicle shape would influence these strategies. Related opportunities in the fields of biology and biomechanics include an improved description of animal behavior in turbulent environments, especially for mid-size aquatic organisms that balance swimming with drifting. Educational impacts will include the production of a series of videos that will be distributed online. These videos will provide a unified demonstration of particle motion across size, shape, and buoyancy regimes in both turbulent and laminar flows, in the spirit of the classic National Committee for Fluid Mechanics films.