High-Performance Computing of Flow, Diffusion, and Hydrodynamic Dispersion in Random Sphere Packings
This thesis is dedicated to the study of mass transport processes (flow, diffusion, and hydrodynamic dispersion) in computer-generated random sphere packings. Periodic and confined packings of hard impermeable spheres were generated using Jodrey–Tory and Monte Carlo procedure-based algorithms, mass...
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|Zusammenfassung:||This thesis is dedicated to the study of mass transport processes (flow, diffusion, and hydrodynamic dispersion) in computer-generated random sphere packings. Periodic and confined packings of hard impermeable spheres were generated using Jodrey–Tory and Monte Carlo procedure-based algorithms, mass transport in the packing void space was simulated using the lattice Boltzmann and random walk particle tracking methods. Simulation codes written in C programming language using MPI library allowed an efficient use of the high-performance computing systems (supercomputers). The first part of this thesis investigates the influence of the cross-sectional geometry of the confined random sphere packings on the hydrodynamic dispersion. Packings with different values of porosity (interstitial void space fraction) generated in containers of circular, quadratic, rectangular, trapezoidal, and irregular (reconstructed) geometries were studied, and resulting pre-asymptotic and close-to-asymptotic hydrodynamic dispersion coefficients were analyzed. It was demonstrated i) a significant impact of the cross-sectional geometry and porosity on the hydrodynamic dispersion coefficients, and ii) reduction of the symmetry of the cross section results in longer times to reach close-to-asymptotic values and larger absolute values of the hydrodynamic dispersion coefficients. In case of reconstructed geometry, good agreement with experimental data was found. In the second part of this thesis i) length scales of heterogeneity persistent in unconfined and confined sphere packings were analyzed and correlated with a time behavior of the hydrodynamic dispersion coefficients; close-to-asymptotic values of the dispersion coefficients (expressed in terms of plate height) were successfully fitted to the generalized Giddings equation; ii) influence of the packing microstructural disorder on the effective diffusion and hydrodynamic dispersion coefficients was investigated and clear qualitative corellation with geometrical descriptors (which are based on Delaunay and Voronoi spatial tessellations) was demonstrated.|