[Turbulence et mélange stratifiés géophysiques en laboratoire]
Les écoulements géophysiques de fluides qui sont stablement stratifiés en densité, comme la plupart de l’océan, peuvent être fortement turbulents à petite échelle en raison d’instabilités de cisaillement. Le mélange qui en résulte contrôle le transport vertical de la chaleur et des traceurs qui sont essentiels pour la stratification et la circulation à grande échelle, et donc pour notre climat. Cependant, la physique de la turbulence stratifiée cisaillée reste mal comprise en raison de sa gamme d’échelles extraordinaire et de son intermittence spatio-temporelle. Cet article passe en revue un modèle de laboratoire, le conduit incliné stratifié (SID), qui capture les fondamentaux de cette physique et sa complexité tout en permettant un contrôle et des mesures précis, une combinaison optimale pour stimuler des recherches fructueuses. Nous expliquons comment cet écoulement d’échange le long d’une pente modeste maintient une dissipation turbulente et un mélange élevés tout en restant fortement stratifié, accédant ainsi au régime géophysique pertinent. En mettant l’accent sur le rôle de mesures détaillées, nous soulignons les découvertes clés et les nombreuses questions non résolues autour de la transition vers la turbulence, des dynamiques intermittentes et des paramétrisations du mélange. Le dimensionnement expérimental montre comment perfectionner les mesures optiques tridimensionnel de l’écoulement pour extrapoler ces résultats au régime le plus intense de la turbulence stratifiée géophysique, qui est enfin à portée de main.
Geophysical fluid flows that are stably-stratified in density, like most of the ocean, can be strongly turbulent at small scales as a result of shear instabilities. The resulting mixing controls the vertical transport of heat and tracers that are key to large-scale layering and circulation patterns, including those crucial to Earth’s climate. However, the physics of sheared stratified turbulence remain poorly understood due to their extraordinary range of scales and spatio-temporal intermittency. This paper reviews a laboratory model, the stratified inclined duct (SID), which encapsulates these fundamental physics and complexity while permitting precise control and measurements, a sweet spot to stimulate fruitful research. We explain how this exchange flow down a modest slope sustains high levels of energy dissipation and mixing while remaining strongly-stratified, thereby accessing the relevant geophysical parameter regime. Emphasising the role of detailed measurements, we highlight key discoveries and unsolved questions around the transition to turbulence, intermittent dynamics and parameterisations of mixing. Dimensional design guidelines show how the optical measurements of the full three-dimensional flow field could be perfected to extrapolate laboratory results to the tantalisingly close regime of the most intense geophysical stratified turbulence.
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Mot clés : turbulence, mélange, géophysique, cisaillement, instabilité, intermittence, océan, paramétrage
Adrien Lefauve 1
CC-BY 4.0
@article{CRPHYS_2024__25_S3_A4_0,
author = {Adrien Lefauve},
title = {Geophysical stratified turbulence and mixing in the laboratory},
journal = {Comptes Rendus. Physique},
publisher = {Acad\'emie des sciences, Paris},
year = {2024},
doi = {10.5802/crphys.196},
language = {en},
note = {Online first},
}
Adrien Lefauve. Geophysical stratified turbulence and mixing in the laboratory. Comptes Rendus. Physique, Online first (2024), pp. 1-29. doi : 10.5802/crphys.196.
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