Séminaire de Mécanique d'Orsay

Le Jeudi 13 septembre 2018 à 14h00 - Nouveau bâtiment FAST

Mixing with Complex Patterns: the Impact of Miscible Viscous Fingering and Motile Bacteria

Massachusetts Institute of Technology

Viscous fingering is a hydrodynamic instability that occurs when a less viscous fluid displaces a more viscous one. Instead of progressing as a uniform front, the less viscous fluid forms fingers that vary in size and shape to create complex patterns. The interface created from these patterns affects mixing between the two fluids, and therefore understanding how these patterns evolve in time is of critical importance in applications such as enhanced oil recovery, bioremediation, and microfluidics. This work focuses on experimentally quantifying the impact miscible viscous fingering has on mixing. We use a radial Hele-Shaw cell as an analog of radial flows in porous media, and the local concentration field is measured temporally and spatially with the use of a fluorescein tracer in the injected fluid. We propose a scaling framework that predicts the time of transition between two regimes in the changing interfacial length, and use this information in combination with concentration gradient information to present an overall scaling framework for the growth of the mixing zone, and the overall rate of mixing observed experimentally. With this understanding, we seek to explore how replacing the previously inactive invading fluid with a suspension of motile E. coli capable of collective swimming will change the interface and subsequently the mixing zone between the two fluids. Most notably, we observe a “rafting” phenomenon where some of the bacteria group together and form a patterned interface between the two fluids. We quantify the impact these active suspensions have on the formation of viscous fingering patterns between the two fluids, and -conversely-report details of the collective swimming behavior in the presence of a viscous-gradient front.

Accès Nouveau bâtiment FAST