Abstract: Stably-stratified turbulence and the enhanced mixing across density isosurfaces that it accomplishes are crucial but inadequately-understood components of many deep-ocean and coastal flow systems of importance for a changing climate. One of the challenges in density-stratified turbulence is to understand the relationship between flow “beasts” (e.g. waves, shearing, and rotational flow structures) and the intricate turbulent mixing process. The first step to tackle this problem is to seek and capture the beasts living in the stratified shear layers. The techniques of advanced measurement and velocity decomposition allow us to obtain the shape, growth, and interactions of these beasts. In this talk, I will first present how we capture the structures experimentally and provide observational evidence of two different beasts: Holmboe waves and vortical structures. I will then show the morphology and evolution of these structures and their relationship with stratification. Finally, I will discuss the geometry of stratified turbulent mixing, focusing on the local alignment between structures, density gradients, and dissipation.

Short Bio: Dr Xianyang Jiang is currently a Research Associate in the Department of Applied Mathematics and Theoretical Physics (DAMTP) at the University of Cambridge. He earned his Ph.D. from the College of Engineering at Peking University in January 2020, focusing on the experimental reconstruction of flow structures, such as three-dimensional waves and vortices, in transitional and turbulent boundary layers. Following this, he gained postdoctoral experience at Cambridge. He is part of the Environmental and Industrial Fluid Dynamics research group and works within the G.K. Batchelor Laboratory. His current work primarily involves conducting experiments on stratified shear flows in an inclined duct and gaining insight into the mixing process from a structural perspective. His research interests centre around the origin, evolution, interaction, and mixing roles of coherent structures in both wall-bounded and stratified turbulence.