Date of Thesis
We present experiments studying the motion and active mixing of swimming mi- crobes in laminar, vortex-dominated fluid flows. We are testing a theory that predicts the existence of swimming invariant manifolds (SwIMs) - invisible, one-way barriers blocking the paths of self-propelled tracers in the flow in one direction. We also pro- pose that the SwIMs together can form chute structures in three-dimensional phase space that facilitate cross-vortex transport of the microbes. We also observe evidence of how these structures promote long-range transport at different non-dimensional velocities (microbe’s velocity relative to flow velocity). Long-range transport is quan- tified by measuring the growth of the variance of an ensemble of particles over time. Our experiments show that at v0 = 0.4, the system is diffusive-like, as opposed to the sub-diffusion observed at lower velocities, while at v0 = 0.5, the transport looks super- diffusive. Sub-diffusive behaviors can be explained by considering the co-existence of ordered and chaotic regions in the flow for small swimming speed, where microbes can get caught around islands of ordered trajectories, mimicking trapped-like behav- iors. Evidence of the coexistence of ordered and chaotic trajectories will be presented through Poincar ́e sections of the flow, and chaotic mixing is observed through expo- nential separation between trajectories.
Biophysics, Active matter, Fluid Mechanics, Chaos, chaotic mixing, active matter, Swimming microbes
Bachelor of Science
Minor, Emphasis, or Concentration
Le, Nghia, "Long-range and Chaotic Active Mixing of Swimming Microbes in a Vortex Chain Flow" (2023). Honors Theses. 664.