Laboratory study of turbulent gravity currents on a continental slope

• Main Author: Décamp, Sabine
• Other Authors: Laboratoire des Écoulements Géophysiques et Industriels Grenoble (LEGI), Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Centre National de la Recherche Scientifique (CNRS)-Université Joseph Fourier - Grenoble 1 (UJF), Université Joseph-Fourier - Grenoble I, Joël Sommeria([e-mail])
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2005
• Subjects: Gravity currents; mixing; oceanic convection; cyclonique vortices; rotating flows; stratified flows; Courants de gravité; turbulence; mélange; convection océanique; tourbillons cycloniques; fluide tournant; fluide stratifié; [SDU.OCEAN]Sciences of the Universe [physics]/Ocean; Atmosphere; Tourbillons; Denmark Strait
• Online Access: https://tel.archives-ouvertes.fr/tel-00011713; https://tel.archives-ouvertes.fr/tel-00011713/document; https://tel.archives-ouvertes.fr/tel-00011713/file/mainToutb.pdf

This study characterizes the dynamics of a turbulent gravity current flowing down a uniform slope in a rotating media. These dense overflows are of particular interest in oceanography since it is an important mechanism in renewing deep water as part of the global thermohaline convective cycle. The large Coriolis turntable (LEGI) is used to study at the laboratory scale, a gravity current in similarity with the oceanic scales. The propagation of such currents is strongly influenced by rotation, bottom topography and mixing with the ambient fluid, that induce unstable dynamics. Interactions between the gravity current and the ambient fluid, due to entrainment and detrainment phenomena, control the stabilization depth of the main current along the coast, as well as its velocity and density. Scaling laws are derived, describing the main properties of the flow along the slope, where the buoyancy flux is conserved. This highly turbulent regime leads to a self-similar behaviour of the flow. Analysis of experimental results allowed to check these scaling laws and to study the turbulent structure of the flow. Large scale instabilities are observed, generating cyclonic vortices also visible in oceanic flows. The sudy of their characteristics suggests the mechanism of their formation. A qualitative comparison of experimental results was made with in-situ measurements in the Denmark Strait Overflow. La dynamique des courants de gravité turbulents sur une pente uniforme en rotation est analysée par des expériences. Ces écoulements denses jouent un rôle important en océanographie dans le renouvellement des eaux profondes qui font parties du cycle de convection thermohaline global. La grande cuve tournante Coriolis (LEGI) permet d'étudier à l'échelle du laboratoire un courant de gravité en similitude avec les échelles océaniques. La propagation de ces courants est fortement influencée par la rotation et le mélange turbulent avec le milieu ambiant, et sa dynamique est instable. Les interactions entre le courant et le milieu ...