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THEORETICAL AND EXPERIMENTAL STUDY OF THE INNER STRUCTURE OF STEADY-STATE DENSITY CURRENTS

English title THEORETICAL AND EXPERIMENTAL STUDY OF THE INNER STRUCTURE OF STEADY-STATE DENSITY CURRENTS
Applicant De Cesare Giovanni
Number 159249
Funding scheme Project funding (Div. I-III)
Research institution Plateforme de constructions hydrauliques EPFL ENAC IIC PL-LCH
Institution of higher education EPF Lausanne - EPFL
Main discipline Civil Engineering
Start/End 01.09.2015 - 31.08.2019
Approved amount 246'465.00
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All Disciplines (2)

Discipline
Civil Engineering
Geomorphology

Keywords (5)

density currents; concentration measurements; averaging techniques; velocity measurementes; steady-state

Lay Summary (French)

Lead
Courants de densité ou gravité sont des écoulements géophysiques causés par la différence de densité entre deux fluides en contact. La décharge de polluants sur les rivières, de pétrole dans les océans et les décharges des usines de désalinisation sont des exemples de courants de densité provoquées par l'homme avec des impacts négatifs sur l'environnement. La réduction de la capacité des réservoirs causée par la déposition des sédiments transportés par les courants de turbidités et les intrusions de salinité sur les estuaires sont des problèmes qui concernent actuellement les ingénieurs et scientists. Les courants de densité jouent un rôle écologique de transport de nutriments et re-oxygénation des lacs, océans et zones pélagiques.
Lay summary

Contenu et objectifs du travail de recherche

Ce travail de recherché a pour but la caractérisation expérimentale de la structure turbulente de l’écoulement de courants de densité permanent et la définition d'un cadre théorique pour sa modélisation. Le programme expérimentale inclut des essais en laboratoire des courants d’alimentation continue, avec des mesures de vitesses instantanées à l’intérieure des courants et les mesures de concentration. Des équations de base seront dérivées d'une façon physiquement soutenu.

Contexte scientifique et social du projet de recherche

On trouve des courants de densité au détroit de Gibraltar, causées par les différences de salinité entre la méditerranée et l’océan, ou au lac Léman quand l'eau du Rhône, plus dense, déverse vers la profondeur. Les courants de densité sont responsables pour des impacts morphologiques sur les lits des rivières, lacs et océans, pour la destruction des câbles sous-marins, et pour la réduction de la capacité de rétention des lacs et réservoirs. Des intrusions salines comme celle du delta Rhine-Meuse (South Holland) quand les barrières de protection contre les crues s’ouvrent sont un autre exemple d’impact négatif des courants de densité. Le développement des modèles pour les mécanismes physiques des courants de densité est la base pour le développement de mesures de mitigation et prévention de ses effets négatives ainsi que pour la compréhension des implications of ceux dans des processus écologiques dans des masses d'eau. 

 

Direct link to Lay Summary Last update: 20.07.2015

Responsible applicant and co-applicants

Employees

Name Institute

Publications

Publication
Continuously-fed density currents over impermeable and porous substrates
VenuleoSara (2020), Continuously-fed density currents over impermeable and porous substrates, EPFL, Lausanne, Switzerland.
Continuously-fed gravity currents propagating over a finite porous substrate
Venuleo Sara, Pokrajac Dubravka, Schleiss Anton J., Franca Mário J. (2019), Continuously-fed gravity currents propagating over a finite porous substrate, in Physics of Fluids, 31(12), 126601-126601.
Experimental results of gravity currents travelling over a fissured bed
VenuleoSara, SchleissAnton (2019), Experimental results of gravity currents travelling over a fissured bed, in E-proceedings of the 38th IAHR World Congress, Panama City, PanamaIAHR, Madrid, Spain.
Distinctive features of horizontal and vertical velocity profiles in turbidity and saline density currents
NomuraShun, SakaguchiHide, De CesareGiovanni, VenuleoSara, HitomiJumpei, MuraiYuichi, TasakaYuji (2018), Distinctive features of horizontal and vertical velocity profiles in turbidity and saline density currents, in Proc. of the 5th IAHR Europe Congress on New Challenges in Hydraulic Research and Engineering, Trento, ItaliaIAHR, Madrid, Spain.
Depth-averaged momentum equation for gravity currents with varying density: coefficient in pressure term
Pokrajac Dubravka, Venuleo Sara, Franca Mário J. (2017), Depth-averaged momentum equation for gravity currents with varying density: coefficient in pressure term, in Journal of Hydraulic Research, 56(3), 424-430.

Collaboration

Group / person Country
Types of collaboration
UNESCO-IHE Institute for Water Education Netherlands (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
Institute of Hydraulics and Road Infrastructures of the Polytechnic University of Marche Italy (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
Department of Engineering, University of RomaTre Italy (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication

Abstract

Density or gravity currents are geophysical flows driven by density differences between two contacting fluids with pertinence to engineering sciences. The release of pollutants into rivers, oil spillage in the ocean and desalination plant out flows are examples of anthropogenic density currents with negative environmental impacts. The loss of storage in reservoirs caused by the deposition of sediments transported by turbidity currents, and salinity intrusions like those verifed in the Rhine-Meuse delta (south Holland) when barrier gates operate, are examples of actual concerns to engineers and scientists. Density currents play also an ecological role in the transport of nutrients and re-oxygenation of water bodies.Although deriving typically from transitory processes, density currents found in nature may have a duration compatible with the assumption of a steady-state process after the passage of the front and a transitional region. More specifically, the time-scale of the development of density currents in nature is typically long enough to verify steadiness of temporal statistics before the current dumping and eventual extinguishing. Examples of steady (or quasi-steady) state currents found in nature are the saline under-flow from Mediterranean sea to the Atlantic ocean observed in the Gibraltar straight and the turbidity current observed when the river Rhone flows into lake Geneva.A proper understanding of the physical mechanisms intrinsic to density currents is the basis to produce adequate preventing and mitigating measures against their negative effects, as well as to understand their implications in the ecological processes in natural water bodies. Most of the research efforts in gravity currents concerns flows developing over smooth beds, few contributions having studied the effect of bed roughness in their dynamics. Moreover, developments on the mathematical formulation of bottom density currents are still needed in order to account for the presence of spatial and temporal varying lower and upper boundaries, with appropriate physical-meaningful terms.This work aims at characterizing experimentally the structure of the flow of turbulent steady-state bottom density currents, to assess the effect of bed roughness and slope on these, and to provide a new theoretical framework for density currents ensuing from averaging techniques recently applied to the description of other environmental flows. A theoretically-derived and empirically-supported conceptual model for dispersive-type fluxes in the lower and upper current boundaries will allow characterizing transfer processes and flow resistance.A research program is proposed where developments in the basic transport equations are complemented with laboratory work, to provide the first supporting empirical evidence. The proposed experimental program includes instantaneous velocities and concentration measurements on a continuously fed density current. Empirical data will be treated with upscaling techniques, where spatial and temporal intermittency is considered, allowing an analysis of the hydrodynamics variables present in the basic hydrodynamic equations and testing the envisaged theoretical framework.
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