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Vortex dynamics and wakes

Interactions of plumes with density-stratification

Contacts: Julie Albagnac, Dominique Anne-Archard, Pierre Brancher

This axis aims at a better understanding of the mixing mechanisms in density stratifications (oceans, atmospheres, industrial devices involving large retention tanks, etc.). For the sake of modeling the mixing,  a vortex ring, representative of a plume or a thermal, is propagating in an ambient fluid whose density evolves linearly in the direction of gravity. The control parameters of our experimental device are: the vortex ring intensity, the stratification stiffness and the vortical structure angle of propagation. It is also possible to generate several consecutive rings. Figure shows an illustration of a vortex ring impacting orthogonally the stratification. 

Visualization, by adding dye to the stratified layer, of a light vortex ring that propagates downwards into a stratification (snapshots 1 to 4), reaches a maximum depth of penetration (snapshot 4), rises back in the light upper layer by buoyancy effect (snapshots 4 to 7) and creates disorder (snapshots 7 to 10).

Vortex dynamics in non-newtonian viscoelastic fluids

Many flows, both environmental and industrial, involve fluids with original rheology. Some are shear-thinning : their viscosity decreases with shear, or the other way around, shear-thickenning. Some fluids exhibit elastic effects. As examples we can cite lava flows, most of the fluids used in the food industry, granular flows when modeled on a large scale, oil etc. For these flows with particular physical characteristics, transport and mixing mechanisms widely studied for Newtonian fluids (ie, for which the strain is directly proportional to the stress) such as water or air, are no longer valid. In this axis, we address the kinematics of a viscoelastic vortex ring evolving in a fluid initially at rest. An illustration is presented hereafter. In the top row, one can follow a vortex ring propagating in water. On the bottom row, the vortex ring is generated in a tank filled with a viscoelastic solution. The kinematics of the vortex structure in these two configurations is very different. Having a better understanding of the physics of a vortex ring propagating in a non-Newtonian fluid would eventually allow transport or mixing optimization of this kind of solution.


Time evolution of a vortex ring generated in water (top row) and a vortex ring generated in a Zetag viscoelastic solution (bottom row). In water, the vortex ring propagates downwards with a quasi-constant velocity. In the viscoelastic solution, the vortical structure propagates downwards (snapshots 1 to 3), stops (without wall !) and goes back upwards (snapshots 3 to 4) like a yoyo.

Dynamics of a particle in the vicinity of a vortex

Many flows are heterogeneous, transporting dispersed particles. For instance, one can cite volcanic fumes, clouds, fluids in food or pharmaceutical industry, etc. For all these applications, it is important to describe interactions between a particle, or a set of particles, and the surrounding flow. The objective of this project is to study the weak coupling of a single light inertial particle evolving in the vicinity of a vortex ring, considered as a model vortex structure. The particle trajectory, along with the vortex ring propagation, is followed thanks to 3D visualization.

Two examples of a light inertial particle trajectory (black curve) evolving in the vicinity of a propagating vortex ring (colored in gray and located in the image bottom at the time of the photo). On the left, the particle is slightly deflected by the vortex ring, but quickly regains its initial rectilinear trajectory. On the right, after an ascending and rectilinear vertical trajectory, the particle has been trapped by the vortical structure and turns around the heart of the vortex ring while being carried towards the bottom of the tank.

Kinematics and wake of freely falling cylinders at moderate Reynolds numbers

Contacts: Patricia Ern, Véronique Roig
PhD Thesis : Clément Toupoint (2019)

For cylinders in free fall in a liquid at rest in the inertial regime, we explore the diversity of motions and associated wakes over a large range of control parameters (cylinder elongation ratio and volume) in order to find generic scaling laws for the body motion.

Different types of vortex shedding in the wake of a cylinder falling in a liquid at rest associated with different paths (From Toupoint et al., J. Fluid Mech., 2019)

Flow induced by a freely rising bubble confined in a thin-gap cell

Contacts: Sébastien Cazin, Véronique Roig,Patricia Ern,
Collaboration: L. Pavlov, M. Cachile and M. V. D’Angelo (Univ. Buenos-aires, Argentina)

We explore the specific complex 3D organization of the motion induced by a bubble freely rising in a thin-gap cell in the inertial regime.

Exploration by Shake-the-Box technique of the 3D perturbation induced by an oscillating confined bubble (From Pavlov et al., Exp. Fluids, 2021)