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Preferential flow dynamics in the vadose zone of fractured and fractured-porous media: Development of a parallelized multi-scale Smoothed Particle Hydrodynamics model

dc.contributor.advisorKordilla, Jannes Dr.
dc.contributor.authorShigorina, Elena
dc.titlePreferential flow dynamics in the vadose zone of fractured and fractured-porous media: Development of a parallelized multi-scale Smoothed Particle Hydrodynamics modelde
dc.contributor.refereeKordilla, Jannes Dr.
dc.description.abstractengThe main objective of this thesis is the development of a smoothed particle hydrodynamics (SPH) model to study preferential flow dynamics in partially saturated porous-fractured media at core- and micro scale. The research is focused on the numerical investigation of preferential flow in the vadose zone, including the estimation of geometrical and hydraulic properties of the subsurface, such as wettability, surface roughness, hydraulic conductivity, and infiltration rate, which are influencing the infiltration dynamics under saturated, unsaturated and partially saturated conditions. In the first part of the thesis the simulation results of sessile and transient droplets on hydrophobic and hydrophilic structured rough surfaces are presented. The results show that the effective static contact angles of Cassie and Wenzel droplets on a rough surface are greater than the corresponding micro scale static contact angles. As a result, micro scale hydrophobic rough surfaces can also exhibit effective hydrophobic behavior. This study considers, as well, the impact of the roughness orientation (i.e., an anisotropic roughness) and surface inclination on droplet flow velocities. The results show that droplet flow velocities are lower if the surface roughness is oriented perpendicular to the flow direction. The second part deals with the investigation of infiltration instabilities in smooth and rough fractures, focusing on the influence of roughness and injection rate on fluid flow modes and flow velocity. Both the rough and smooth fractures exhibit flow instabilities, fingering, and intermittent flow regimes for low infiltration rates. A flat fluid front is achieved when the flux supplied to a fracture is larger than the gravitationally driven saturated flux. An increase in roughness decreases the flow velocity and increases the standard deviation of velocity. This is caused by a higher likelihood of flow discontinuities in the form of fingering and/or snapping rivulets. The scaling of specific discharge with normalized finger velocity and the relationship between fingertip length and scaled finger velocity are in a good agreement with experimental results. The final part is devoted to a newly developed fully-coupled multi-scale SPH model, which considers flow through a porous matrix governed by the volume-effective Richards equation, and discrete free-surface flows governed by the Navier-Stokes equation. Inflow dynamics from the fracture into the porous matrix are realized by an efficient particle removal algorithm and a virtual water redistribution formulation in order to enforce mass and momentum conservation. The model validation is carried out via comparison to a FEM model (COMSOL) for the Richards based flow dynamics and laboratory experiments to cover more complex cases of free-surface flow dynamics and matrix infiltration. The developed model is employed to investigate preferential flow dynamics at a fracture-matrix interface. Simulation results show that preferential flow occurs in most cases simultaneously with the diffuse flow. Depending on the infiltration rate, the ponding effect can be dominant until the matrix saturation is high enough to activate fracture flow. For extremely high infiltration rates, fracture flow is dominant and ponding occurs when the fracture space is fully saturated. Next, the model is employed to simulate infiltration dynamics in rough fractures embedded in impermeable and permeable porous walls for different infiltration rates. The simulation results indicate a delay in arrival times for fractures with permeable walls in comparison to impermeable fractures, especially for small infiltration rates. Here, for higher infiltration rates, water flows rapidly to the bottom of the fracture without any significant delay in arrival
dc.contributor.coRefereeTilgner, Andreas Prof. Dr.
dc.contributor.thirdRefereeSauter, Martin Prof. Dr.
dc.contributor.thirdRefereeGu, Hongbiao Prof. Dr.
dc.contributor.thirdRefereeNeuweiler, Insa Prof. Dr.
dc.contributor.thirdRefereePtak, Thomas Prof. Dr.
dc.subject.engpreferential flowde
dc.subject.engvadose zonede
dc.subject.engnumerical SPH modelde
dc.affiliation.instituteFakultät für Geowissenschaften und Geographiede
dc.subject.gokfullHydrologie (PPN613605179)de

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