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Title:  Particle dispersion in isotropic turbulence and unsteady particle dynamics at finite Reynolds number 
Author(s):  Mei, Renwei 
Doctoral Committee Chair(s):  Adrian, Ronald J. 
Department / Program:  Mechanical Science and Engineering 
Discipline:  Theoretical and Applied Mechanics 
Degree Granting Institution:  University of Illinois at UrbanaChampaign 
Degree:  Ph.D. 
Genre:  Dissertation 
Subject(s):  Applied Mechanics
Engineering, Mechanical Physics, Fluid and Plasma 
Abstract:  A solution to particle dispersion in an isotropic turbulence under Stokes drag, Basset force and gravitational force is obtained in closed form using the independence approximation. The Basset force has no effect on the fluid velocity structure seen by the particles or the longtime particle diffusivities. It does affect the intensities of particle motion for particles with large settling rate and with response time comparable to the turbulence integral time scale. A solution for particles dispersion in isotropic turbulence with nonStokesian drag and gravitational force is obtained. The time constants of the particle fluctuation in the directions parallel and perpendicular to the gravity are anisotropic. Turbulence increases particle response time constants and reduces settling velocity. Influence of the nonlinear drag, particle response time constants and settling rate on particle dispersion are investigated. MonteCarlo simulations are performed for particle motions in an isotropic turbulence with nonStokesian drag. Pseudoturbulence is generated using random Fourier modes representation. Statistical averages are obtained from more than 5000 particles. The results of the simulation validate the preceeding analysis in the nonStokesian drag range. The influence of turbulence structure on the dispersions of fluid and particle is examined. In addition to the integral length and time scales, the functional form of the energy spectrum is also important in describing the dispersions of both fluid and particles. Numerical solution for unsteady flow over a sphere indicates that the addedmass force at finite Reynolds number is the same as in the creeping flow and the potential flow. The classical Stokes solution is not valid at small frequency, $\omega$, and the corresponding Basset force is proportional to $\omega$, instead of $\sqrt{\omega}$. The Bassetforce term has a kernel decays faster than (t $\tau$)$\sp{1/2}$ at large time. The use of the steady state drag coefficient with the instantaneous velocity is justified to approximate the quasisteady drag on particles. Limiting behavior of the unsteady drag on a sphere at small frequency and low Reynolds number is obtained using matched asymptotic expansions. The modified Bassetforce term at finite Re is constructed. It has a kernel decays as (t $\tau$)$\sp{2}$ at large times. 
Issue Date:  1990 
Type:  Text 
Language:  English 
URI:  http://hdl.handle.net/2142/20760 
Rights Information:  Copyright 1990 Mei, Renwei 
Date Available in IDEALS:  20110507 
Identifier in Online Catalog:  AAI9114344 
OCLC Identifier:  (UMI)AAI9114344 
This item appears in the following Collection(s)

Graduate Dissertations and Theses at Illinois
Graduate Theses and Dissertations at Illinois 
Dissertations and Theses  Mechanical Science and Engineering