Fluid Mechanics Seminar: Jean-Pierre Hulin

Density contrasts and the influence of solid walls play a key part in the circulation of fluids in systems like chemical reactors, oil wells and in some subterranean or oceanic flows.

We study this problem in the case of the spontaneous mixing of two miscible fluids of different densities, each of them occupying initially half of the length of a tilted tube (in a gravitationally unstable configuration) and put in contact with a zero mean flow. The flow structure reflects a balance between axial gravity inducing the interpenetration, transverse mixing due to the Kelvin-Helmoltz instability and stratification due to transverse gravity.

While, for a nearly vertical tube, turbulent mixing is efficient across the whole flow section, one observes closer to horizontal a stratified laminar flow with three layers of different densities or, even, a fully separated counterflow. Counterintuitive effects have been observed such as the increase of the interpenetration velocity when the tilt angle from vertical or the viscosity of the two fluids increase.

The local structure of the flow and of the concentration distribution has been studied by PIV and LIF techniques. This allowed one to characterize quantitatively the mixing process in these different configurations and, more specifically, its stationarity and the mechanisms of the transverse exchange of mass and momentum.

†With with F. Moisy, D. Salin, T. Séon, Y. Tanino and J. Znaien.
In cooperation with: J. Magnaudet, Y. Hallez (IMFT), E.J. Hinch (DAMTP-CMS), G.M. Homsy (UCSB, UBC) and B. Perrin (LPA-ENS).