Coherent Structures as Transporters: From Particle-Laden Vortex Rings to Internal Wave Generation

Coherent vortical structures play a central role in transport, mixing, and momentum redistribution in complex fluid environments. In this seminar, I will present recent experimental results obtained at the Institut de Mecanique des Fluides de Toulouse on the dynamics of vortex rings interacting with dispersed particles and stable density stratification.
We first investigate the interaction between a vortex ring and an isolated inertial particle. Distinct regimes of interaction are identified experimentally, ranging from weak perturbation to strong coupling and capture-like dynamics. A simplified model based on the Maxey-Riley equation allows to identify the dominant hydrodynamic forces. These results provide a framework for understanding particle transport by coherent vortical structures and mapping the interaction regimes.
We then consider the propagation of vortex rings in a stably stratified environment. A vortex ring initially generated in a homogeneous light layer propagates downward into a density-stratified fluid, decelerates under buoyancy effects, and subsequently reverses its motion. Time-resolved volumetric PIV measurements reveal a complex reorganization of vorticity, involving baroclinic vorticity generation and interaction with the primary vortex. Simultaneously, internal gravity waves are emitted and interact with the evolving flow. Two configurations are examined: a normal impact on isopycnals and an oblique incidence at 60° relative to the density interfaces. These experiments provide a full three-dimensional picture of vortex-ring reconfiguration and wave generation mechanisms.