Ph.D. Thesis Defense by Xuemei Wu
Wednesday, February 7, 2001

(Drs. Mostafa Ghiaasiaan and Said Abdel-Khalik, co-advisors)

"Monte-Carlo Modeling of Turbulent Dispersion of Small Particles in Channels"

Abstract

Particle-laden gas flows occur in numerous natural and industrial processes, and have been extensively studied in the past. Highly successful, hybrid computational fluid dynamic (CFD)-based models that are based on the Eulerian analysis of the carrier fluid and the stochastic, Lagrangian analysis of large numbers of randomly selected particles (particle tracking), have recently been developed. The particle-turbulent eddy interactions are modeled by using appropriate stochastic eddy characteristics. The objectives of this study were to: (a) develop a mechanistic Eulerian-Lagrangian model, based on the various currently-applied Reynolds-Averaging Navier-Stokes (RANS)-type turbulence models, and particle dispersion models applicable to microscopic particles; and (b) perform parametric simulations and examine the suitability of the RANS-type CFD models for the analysis of the transport and deposition of aerosols in channels.

The CFD code KIVA-3, originally developed at Los Alamos National Laboratory, was used as the basis for model development, and was equipped with the Reynolds Stress Transport (RSM) models. For the Lagrangian particle tracking, the modeled forces that act on particles included the drag, gravitation, thermophoresis, and the shear-induced (Saffman) lift force. The effect of the  Brownian motion was modeled as a random white noise term in the particle equation of motion.

The correctness and accuracy of the turbulence models were verified by comparison of model predictions with experimental data. Extensive parametric simulation were conducted whereby the effects of various forces, and their dependence on particle size and the channel Reynolds number, were examined. The simulation results, in addition to providing important trends associated with the physical processes involved in the transport and dispersion of microscopic particles, showed that the aforementioned forces should all be considered in the simulation of mm and sub-mm particle dispersions. The results also showed that using current RANS-type hybrid methods for detailed simulations of aerosol transport and removal in common physical systems maybe overly expensive with respect to computations. Further research aimed at simpler physical models, and more robust and efficient numerical analysis methods, were accordingly recommended.