Concentration Statistics in Heterogeneous Flow Fields

Prezentare - Dr. Marco Denz

Universitatea Politehnica din Catalunia - Grupul de Hidrologie Subterana

25 noiembrie 2010

Spatial and temporal heterogeneity of ambient natural environments play a significant role in large scale transport phenomena.  Uncertainty about spatio-temporal fluctuations in system parameters (e.g., flow velocity) make deterministic predictions of macroscopic

 systems states (e.g., solute concentration) elusive.Distributions of system states generally exhibit highly non-Gaussian behavior, which cannot be captured solely by the corresponding mean and variance. Instead, these features of transport are described by the probability density function (PDF) of a system state, e.g., the PDF of concentration at a certain point in space and time. We study the PDF of the distribution of a passive scalar that disperses in a random velocity field. We derive an explicit map between the velocity distribution and the scalar PDF, and obtain approximate solutions for the PDF of the normalized scalar. These solutions allow for the explicit quantification of the impact of dispersion on the evolution of the passive scalar PDF without recurrence to classical closure approximations in terms of mixing models. 

 
 
septembrie 2017
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SEMINARIO DEL GRUPO DE

HIDROLOGÍA SUBTERRÁNEA

UNIVERSIDAD POLITÉCNICA DE CATALUÑA

"Experimental Upscaling of Flow and Transport in Porous Media"

(autores: A. Englert, N. Güting, T. Vaitl, T. Griese and T. Gökpinar)

a cargo de

Andreas Englert (Ruhr-University Bochum)

 

Día: MIÉRCOLES, 5 de Octubre de 2011

Hora: 12.15 hrs.

Lugar: Aula CIHS (Planta Baja). Departamento Ingeniería del Terreno (módulo D2-UPC).

Andreas Englert (Ruhr-University Bochum)

Día: MIÉRCOLES, 5 de Octubre de 2011

Hora: 12.15 hrs.

Lugar: Aula CIHS (Planta Baja). Departamento Ingeniería del Terreno (módulo D2-UPC).

Abstract:

While the physics of mixing and reaction is well understood at the pore scale, the quantification of these processes at the scales relevant for applications is highly challenging. The inability to sample all the subsurface spatial heterogeneity implies that the processes involved need to be averaged. The loss of information induced by this procedure causes anomalous behaviors of the upscaled dispersion and reaction rates. As mathematical and numerical upscaling of such processes is challenging and such upscaling procedures need to be verified to become useful for proper transport prediction, the project here focuses on experimental laboratory scale upscaling of flow and transport. 
In a first study we examined the potential of laboratory sandbox experiments and studied in detail the impact of the injection near field on the larger scale transport process. Thereto we filled a sandbox with sediments, which were characterized for hydraulic conductivity prior to filling. The latter was then accomplished in such way that different source zone release conditions were arranged by modifying the hydraulic conductivity of injection near-field, while the surrounding hydraulic conductivity field remained unchanged. The experiments in this first sandbox model gave us confidence in laboratory sandbox models and showed that source zone release conditions are of importance for plume development. In detail, we found that source zone release conditions affect the first and second temporal moments, corresponding to the mean arrival time and the spreading of breakthrough curves and the spatial spreading of solute plumes in both the longitudinal and the transverse direction. We further found that in future experiments monitoring of the injection function and subsequent consideration of the measured injection function in the analysis of breakthrough curves might be beneficial for proper parameter estimation. 
In a second study we examined flow and transport in cube shaped sediment samples before and after freezing. Thereto we developed a cube shaped experimental setup, which allows for fill of sediment, performance of flow and transport experiments, freezing of the entire apparatus and withdrawal of a frozen sediment cube from the apparatus. This is an ongoing study. However, first results suggest that the apparatus works and there are only small changes in flow and transport parameters pre- and post- freezing. This is promising for the following experiments. In future studies the frozen sediment cubes will be utilized to arrange heterogeneous sediment formations in sandboxes. Thereto development of an apparatus is ongoing, which will allow to utilize the well explored frozen sediment cubes from experiments in the cube shaped experimental setup. Such experiments will allow experimental upscaling from the dm- to m-scale of the following processes: flow, conservative transport, reactive transport, reactive transport including feedbacks (precipitation and dissolving).

El seminario se podrá ver publicado la próxima semana en la página del grupo: www.h2ogeo.upc.es