Dissertation/Thesis Abstract

Dynamics of settling charged particles in turbulence: Theory and experiments
by Lu, Jiang, Ph.D., Michigan Technological University, 2010, 185; 3439129
Abstract (Summary)

It has been proposed that inertial clustering may lead to an increased collision rate of water droplets in clouds. Atmospheric clouds and electrosprays contain electrically charged particles embedded in turbulent flows, often under the influence of an externally imposed, approximately uniform gravitational or electric force. In this thesis, we present the investigation of charged inertial particles embedded in turbulence.

We have developed a theoretical description for the dynamics of such systems of charged, sedimenting particles in turbulence, allowing radial distribution functions to be predicted for both monodisperse and bidisperse particle size distributions. The governing parameters are the particle Stokes number (particle inertial time scale relative to turbulence dissipation time scale), the Coulomb-turbulence parameter (ratio of Coulomb 'terminalar speed to turbulence dissipation velocity scale), and the settling parameter (the ratio of the gravitational terminal speed to turbulence dissipation velocity scale). For the monodispersion particles, The peak in the radial distribution function is well predicted by the balance between the particle terminal velocity under Coulomb repulsion and a time-averaged 'drift’ velocity obtained from the nonuniform sampling of fluid strain and rotation due to finite particle inertia.

The theory is compared to measured radial distribution functions for water particles in homogeneous, isotropic air turbulence. The radial distribution functions are obtained from particle positions measured in three dimensions using digital holography. The measurements support the general theoretical expression, consisting of a power law increase in particle clustering due to particle response to dissipative turbulent eddies, modulated by an exponential electrostatic interaction term. Both terms are modified as a result of the gravitational diffusion-like term, and the role of 'gravity’ is explored by imposing a macroscopic uniform electric field to create an enhanced, effective gravity.

The relation between the radial distribution functions and inward mean radial relative velocity is established for charged particles.

Indexing (document details)
Advisor: Shaw, Raymond
Commitee: Cantrell, Will, Lee, Seong-Young, Mazzoleni, Claudio
School: Michigan Technological University
Department: Physics
School Location: United States -- Michigan
Source: DAI-B 72/03, Dissertation Abstracts International
Subjects: Atmospheric sciences
Keywords: Charged particles, Clustering, Turbulence, Water droplets
Publication Number: 3439129
ISBN: 978-1-124-43800-9
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