kth_logo.gif

Doctoral defense

Large Eddy Simulation of Particulate Turbulent Channel Flows


Defendant Main Advisor Extra Advisor Date
Koji Fukagata Fritz Bark Said Zahrai 2000-02-11

Opponent
Olivier Simonin, LNH/EDF, France

Evaluation committee
Henrik Alfredsson, KTH Mekanik
A.E. Almstedt, CTH
C. Trädgårdh,

Abstract

This thesis deals with numerical simulations of particulate turbulent channel flows. Turbulent velocity field is simulated using large eddy simulation (LES). Individual particles are tracked by integrating the particle equation of motion, i.e. Lagrangian particle tracking (LPT).

Simulations are first performed with one-way coupling; namely that influence of particles on fluid is neglected. The methodology is assessed through comparisons between statistics computed for 0.07 mm copper particles and 0.05 mm glass particles in a turbulent channel flow of air at Re=180 and earlier data computed using similar methodology. Good agreement is found between these computational results. Motion of 0.00001 m - 0.01 mm graphite particles in a channel flow of air at Re=180 is also simulated. The computed deposition velocity is found to be in good agreement with the empirical relation. In both simulations above, the computed statistics are used to study the importance of different forces acting on the particle.

Subsequently, modulation of turbulence by the presence of 0.07 mm copper and 0.05 mm glass particles in a turbulent channel flow of air at Re=180 is studied by simulations taking into account the force from the particles to the fluid, i.e. two-way coupling.

Finally, influences of inter-particle collisions are investigated. Simulations of 0.07 mm particles in a channel flow of air at Re=644 are compared with the experimental data by Kulik et al. with which all earlier simulation have been shown poor agreement. Inter-particle collisions are found to have significant effects on the particle statistics in whole channel even when the particle mass flow ratio is as low as 2%. Agreement with the experimental data can significantly be improved by taking into account inter-particle collisions and a mechanism which prohibits direct re-entrainmant of particles from the near-wall region to the bulk flow.

The thesis consists of a survey of including required development time for the flows, force balances in the particle phase, modulations in the carier fluid turbulence due to the presence of particles, particle deposition to walls, passive scalar turbulence, inter-particle collisions, increase of drag coefficient and boundary conditions, followed by seven papers describing specific results.


[Download (0.7 Mb)]