Paper Number
BA20
Session
Biological and Active Matters
Title
Mixing of active suspensions in chaotic flow
Presentation Date and Time
October 16, 2018 (Tuesday) 1:55
Track / Room
Track 6 / Tanglewood
Authors
- Blackwell, Brendan C. (University of Pennsylvania)
- Qin, Boyang (University of Pennsylvania)
- Arratia, Paulo E. (University of Pennsylvania, Mechanical Engineering & Applied Mechanics)
Author and Affiliation Lines
Brendan C. Blackwell, Boyang Qin, and Paulo E. Arratia
Mechanical Engineering & Applied Mechanics, University of Pennsylvania, Philadelphia, PA
Speaker / Presenter
Blackwell, Brendan C.
Text of Abstract
In this talk, we examine the effect of swimming bacteria on transport, diffusion, and mixing in weakly chaotic flows. An oscillatory two-dimensional flow is generated by driving a sinusoidal current through a conducting fluid (salt water) that is situated atop an array of magnets. We perform experiments with two different arrangements of the magnets: one that is a neatly ordered lattice to create regular vortices, and on that is random to create a more disordered flow pattern. By changing the frequency and amplitude of the applied voltage we are able to probe Reynolds numbers ranging approximately from 1 to 100, and path lengths of approximately 0.1 to 1, which is sufficient to observe the onset of time-reversal asymmetry. Two types of fluids are used: (1) a simple Newtonian liquid (i.e. water) and (2) a mixture of water and bacteria (Vibrio cholerae). The fluids are seeded with fluorescent particles, and particle-tracking software is used to quantify the flow. Measurements of stretching fields and Lyapunov exponents are used to characterize flow behavior and mixing. Results with plain salt water are compared to results with the addition of varying concentrations of V. cholerae. We find that the addition of active bacteria, even in dilute quantities, results in significant changes to the stretching fields even though the Eulerian velocity fields remain quite similar. We also perform experiments with fluorescent dye, both with and without bacteria, to more directly characterize mixing. These data also show a substantial difference between the active suspension and the control case, even with small concentrations of bacteria.