Lagrangian diffusion in non homogeneous non isotropic turbulence
When particles are released from a localized source in a turbulent flow, they disperse due to flow fluctuations with a spreading rate dictated by the velocity variance and its Lagrangian timescale. This problem of Taylor diffusion is complex in a non homogeneous flow as all properties evolve with the distance to the source. We focus here on the situation of tracer particles released from the center of a von Karman flow and investigate the non-stationary Lagrangian dynamics associated with the Eulerian inhomogeneity and anisotropy. We will then analyze how small scales are affected by the large-scale anisotropy of the flow and explain how the hierarchy of timescales can be understood knowing the large-scale properties of the flow.
In a second part we will show new experiments conducted in the lab to study how ice melts in hot salted water in a configuration leading to the formation of a two layers system. We will show what are the dynamical regimes observed and how fast ice melts depending on the competition between density stratification and turbulent mixing.
Contact Nathanaël Machicoane for more information or to schedule a discussion with the seminar speaker.