Large-scale flow structures and mixing in horizontally extended stratified shear flows

• Applicant: Philipp Vieweg
• Subject Area: Fluid Mechanics
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 532721742

The oceans represent due to their enormous heat capacity the biggest heat sink in weather and climate models. However, our understanding of the occurring turbulent flow structures and thus mixing processes is far from complete. This proposal aims to improve this understanding and to contribute hence to more accurate climate and weather models, as only a reliable projection of the dynamics of the oceans allows to predict climate variations far into the future. Here, a simplified configuration of an oceanic flow shall be used to study in particular the emerging large-scale flow structures and their mixing behavior at the interface within a fluid. We consider a fluid that exhibits a stable stratification, i.e., the fluid is denser at the bottom but less dense at the top. To force turbulence, the fluid shall be sheared - this means that there is a relative motion of different horizontal layers in the fluid to each other. This configuration allows to describe the situation at estuaries pouring into the ocean, or the interface between the mixed layer close to the ocean's surface and the denser deep ocean, in a simplified way. Key questions to answer are: 1) Which characteristic flow structures emerge in such stably stratified shear flows once a horizontally extended domain (as is the case for the ocean) is provided? How does the mixing depend on this horizontal extension? 2) How is the formation of large-scale flow structures affected by rotation around the vertical axis (resembling the Earth's rotation)? 3) What is the particular role of the working fluid? In other words, how are such processes influenced by a variation of the temperature of the fluid (modifying thus its material parameters)? These questions shall be answered by the use of highly resolved, three-dimensional direct numerical simulations. The resulting datasets and research results can subsequently be used to improve the parametrization of oceanic flows (which are simulated under-resolved even today). A thorough understanding of climate variations on Earth has become more important than ever, and so this proposed research aims to make use of the experience of the applicant in simulations of simplified models of geo- and astrophysical convection flows to provide an important contribution.

• DFG Programme: WBP Fellowship
• International Connection: United Kingdom
• Host: Professor Colm-cille Caulfield