Analysis of aerosol particle transport, deposition, removal and resuspension in turbulent flows

The objective of this thesis is to provide a fundamental understanding of transport, deposition, removal and resuspension of spherical particles and ellipsoidal fibers in turbulent duct flows.; Aerosol particle transport and deposition in turbulent channel flows with gravity pointing different directions are studied. The instantaneous fluid velocity field is generated by the direct numerical simulation of the Navier-Stokes equation via a pseudospectral method. Particle equation of motion including Stokes drag, Brownian diffusion, lift and gravitational forces is used for trajectory analysis. Ensembles of 8192 particle paths are evaluated, compiled, and statistically analyzed. The results show that the wall coherent structure plays an important role on the particle deposition process. The simulated deposition velocities under various conditions are compared with the available experimental data and the sublayer model predictions. The results for vertical ducts show that the particle deposition velocity varies with the direction of gravity, and the effect becomes more significant when the shear velocity is small. For horizontal ducts, the gravitational sedimentation significantly increases particle deposition rate on the lower wall.; Particle removal and re-entrainment in the turbulent channel flows generated by DNS are studied. Particle removal mechanisms in turbulent channel flows are examined and the effects of hydrodynamic forces, torques and the near-wall coherent vorticity are discussed. The particle resuspension rates are evaluated, and the results are compared with the model of Reeks. It is found that large size particles move away roughly perpendicular to the wall due to the action of the lift force. Small particles, however, follow the upward flows formed by the near wall eddies in the low speed streak regions. The simulation results suggest that small particles (with $t+p\le 0.023$) primarily move away from the wall in the low speed streaks, while larger particles (with $t+p\ge 780$) are mostly removed in the high speed streaks.; In the third part of the thesis, ellipsoidal particle transport and deposition in the directly simulated turbulent channel flows are studied. The particle equations of motion used include the hydrodynamic forces and torques, the shear-induced lift and the gravitational forces. Euler's four parameters (quaternions) are used for describing the time evolution of particle orientations. The results are compared with those for spherical particles and their differences are discussed. The DNS predictions are compared with the available experimental data and earlier sublayer model simulation results and reasonable agreements are observed. The result shows that the elongated particles deposition rate increases significantly when the aspect ratio increases.