Dense suspensions of swimming bacteria exhibit chaotic flow patterns that promote the mixing and transport of resources and signaling chemicals within cell colonies. While the importance of active turbulence is widely recognized, the structure and dynamics of the resulting collective flows are the subject of intense investigation. Here, we combine microfluidic experiments with proper orthogonal decomposition (POD) analysis to quantify the dynamical flow structure of this model active matter system under a variety of conditions. In isotropic quasi-two-dimensional turbulence, the modal analysis encompasses the most energetic spatiotemporal flow structures across a range of suspension activity levels and benchmarks the potential for low-dimensional order representations of active turbulence. In confined geometries, POD analysis illustrates the role of boundary interactions for the transition to bacterial turbulence, and it quantifies the evolution of coherent active structures in externally applied flows. Beyond establishing the physical flow structures underpinning the complex dynamics of bacterial turbulence, the low-dimensional representation afforded by this modal analysis will facilitate data-driven modeling of active turbulence.

• Received 1 September 2022
• Accepted 24 January 2023

DOI:https://doi.org/10.1103/PhysRevFluids.8.023101