|Ph.D Student||Duman Tomer|
|Subject||Particle Transport at Porous Media Interfaces|
|Department||Department of Civil and Environmental Engineering||Supervisor||Professor Uri Shavit|
|Full Thesis text|
Understanding the mechanisms that control flow and transport at porous media interfaces and canopy flows is relevant to many environmental processes, including atmospheric dispersal of aerosols, pesticide applications, and suspended sediments. The complicated structure of the canopy, which is composed of many small-scale obstacles, is known to significantly affect the flow. Therefore, modeling transport phenomena in such environments is challenging. The objective of this thesis is to study the effects of porous domains and canopies on particle dispersion, and developing models to describe the particles concentration and the flow field needed for this modeling.
The first part of the work is dedicated to laminar canopy flows and is based on accurate numerical calculations for a simplified canopy model. A new tool was developed for the solution of the interface flow problem, named "Apparent Interface Approach". In this approach, the macroscopic velocity profile is obtained by adjusting the location of the interface, without the need for other empirical coefficients.
Particle dispersion that is caused by velocity sub-scale distributions was studied. This kind of dispersion was found to be crucial for heavy particles, showing large variations near the source. Values of dispersion flux as a function of permeability and porosity were obtained through Eulerian-Lagrangian simulations. It was found that this dispersion is not Fickian and that diffusion like models cannot be used.
The second part of the work is dedicated to particle transport in turbulent canopy flows. We implement a Lagrangian stochastic (LS) model in velocity fields that were measured by particle image velocimetery within and above a synthetic canopy model, made of randomly distributed thin microscope slides. The measurements provide data in a spatial resolution that cannot be found in any other work as of today. The LS model results show that the common assumption about the isotropy of the stochastic coefficient and the use of the Taylor's frozen turbulence hypothesis are reasonable for estimating concentration of scalars in canopy flows. However, accurate modeling requires a flow representation that is based on a complete volume averaging. One single profile, positioned arbitrarily, is likely to generate incorrect results.
Finally, the LS model was modified for heavy particle transport. Comparison with demonstration experiments, in which heavy particles were released from a point source, showed the same behavior as the model but differed in values; probably due to differences between the flow conditions at the source in the simulations and during the experiments.