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96 CHAPTER 3. TERRESTRIAL SYSTEMS Cooperation within the institute and with groups outside of the institute 1. Dr. Julia Boike, HGF Young Research Group SPARC, Alfred Wegener Institute, Potsdam 2. Prof. Dr. Peter Bastian and Dr. Olaf Ippisch, Institute of Parallel and Distributed Systems, University of Stuttgart 3. Prof. Dr. Qihao Yu and Prof. Dr. Huijun Jin, Institute for Cold and Arid Regions Environmental & Engineering Research (CAREERI), Chinese Academy of Sciences, Lanzhou, China 4. Dr. Frank Brner, Dresdner Grundwasserforschungszentrum (DGFZ), Dresden 5. Dr. Benedikt Oswald, Paul Scherrer Institute (PSI), Villigen, Schweiz Future Work see Overview Peer Reviewed Publications 1. Leidenberger et al. [2006] 2. Schneider et al. [2006] Diploma Theses 1. Schneider [2005] PhD Theses 1. Braun [2006]
3.1. SOIL PHYSICS 97 3.1.1 Unstable Gravity-driven Fingering Flow in Unsaturated Porous Media Fereidoun Rezanezhad Abstract Wetting front instability, or unstable gravity-driven fingering, can occur during vertical infiltration through initially dry sand. With the aim of studying the physical process concerning of the fingering phenomena in two dimensions, experiments of water infiltration through a Hele-Shaw cell of multi-layered sand were carried out in the laboratory. Using imaging technique, we study the dynamics of water saturation in fingering flow for different flow conditions. depth [m] depth [m] 0 0.2 0.4 width [m] 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 time:15 min a 0 0.1 0.2 0.3 0.4 0.5 width [m] 0 0.2 0.4 0 0.2 0.4 width [m] 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 time:30 min depth [m] 0 0.1 0.2 0.3 0.4 0.5 0 0.2 0.4 width [m] 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 time:75 min width [m] 0 0.2 0.4 0 0.2 0.4 width [m] 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 time:125 min depth [m] 0 0.1 0.2 0.3 0.4 0.5 0 0.2 0.4 width [m] 0 0.2 0.4 width [m] 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 time:200 min original image normalized image deconvoluted image b c d 1.00 0.88 0.75 0.62 0.50 0.38 0.25 0.12 0 depth [m] 0 0.1 0.2 0.3 0.4 0.5 width [m] 0 0.2 0.4 depth [m] 0 0.1 0.2 0.3 0.4 0.5 width [m] 0 0.2 0.4 mobile core immobile fringe Figure 3.1: Left: a) Fingering patterns observed by Light Transmission Method (LTM) during water and dye infiltration into the multi-layered medium. b) Original observed image. c) Normalized image to visualize the water saturation. d) Deconvoluted image using the Point Spread Function (PSF). Right: The separation of the water phase into a mobile component (core) and an immobile one (fringe) observed using dye tracer infiltration. Background and Observations The fluid flow through preferential paths or fingers is important in the hydrological processes of infiltration through the soil profile. Fingered flow in porous media was studied, both in the petroleum industry to better understand oil recovery and in the environmental sciences as an instance of preferential flow of water through soil. Fingered flow occurs in homogeneous coarse grained materials when the infiltration rate is below the saturated hydraulic conductivity (Ks) and gravitational influences on the imbibing solution dominate the forces of capillary. We established such conditions in a Hele- Shaw cell where a layer of fine sand was placed on top of a coarse sand. Flow instability is induced at the transition from the fine-textured sand to the coarse-textured sand. The fingers are disturbed within the heterogenous middle-layer and reappear in the uniform layer below (Fig.1). Funding DFG project RO 1080/9-1&2, 2005- 2006 Methods and results We improved the Light Transmission Method (LTM) to measure the dynamics of water saturation within flow fingers in great detail with high spatial and temporal resolution. This was achieved by adding a deconvolution procedure using the Point Spread Function (PSF) to correct the measurements for multiple light scattering in observed image. The method was calibrated using X-ray absorption. Additionally, after stabilization of the fingered flow pattern, we applied a dye tracer to visualize the velocity field within flow fingers. We analyzed the dynamics of water within the finger tips, along the finger core behind the tip, and within the fringe of the fingers during lateral growth. Our results confirm previous findings of saturation overshoot in the finger tips and revealed a saturation minimum behind the tip as a new feature. The finger development was characterized by a gradual increase in water content within the core of the finger behind this minimum and a gradual widening of the fingers to a quasi-stable state. In this state, a sharp separation into a core with fast convective flow and a fringe with exceedingly slow flow was detected. Main Publication [Rezanezhad et al. , 2006]
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Institut für Umweltphysik und Arbe
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4 CONTENTS 2.4.10 Satellite monitor
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Atmosphere and Remote Sensing 2.1 T
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Bibliography 177
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180 CHAPTER 7. BIBLIOGRAPHY Butz, A
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7.5. INVITED TALKS 193 Invited Talk
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