This thesis combines methods from statistical physics and nonlinear dynamics to advance research on the pattern formation in active fluids in several directions. In particular, it focuses on mesoscale turbulence, a state observed in microswimmer suspensions, which is characterized by the emergence of dynamic vortex patterns. The first major contribution concerns the bottom-up derivation of a frequently used continuum model of mesoscale turbulence from a set of particle-resolved stochastic equations. Utilizing the model, mesoscale turbulence is shown to induce nontrivial transport properties…mehr
This thesis combines methods from statistical physics and nonlinear dynamics to advance research on the pattern formation in active fluids in several directions. In particular, it focuses on mesoscale turbulence, a state observed in microswimmer suspensions, which is characterized by the emergence of dynamic vortex patterns. The first major contribution concerns the bottom-up derivation of a frequently used continuum model of mesoscale turbulence from a set of particle-resolved stochastic equations. Utilizing the model, mesoscale turbulence is shown to induce nontrivial transport properties including a regime of optimal diffusion. The thesis then explores possible strategies of control. One of these relies on an external field that leads to stripe-like structures and can even suppress patterns entirely. The other involves geometric confinement realized by strategically placed obstacles that can reorganize the flow into a variety of ordered vortex structures. The turbulence transition inside an obstacle lattice is shown to have an intriguing analogy to an equilibrium transition in the Ising universality class. As a whole, this thesis provides important contributions to the understanding and control of turbulence in active fluids, as well as outlining exciting future directions, including applications. It includes a substantial introduction to the topic, which is suitable for newcomers to the field.
Henning Reinken has a Bachelor of Science in Energy Engineering and Process Engineering (Energie- und Prozesstechnik) and a Master of Science in Engineering Science (Physikalische Ingenieurwissenschaft) from the Technical University of Berlin (TUB). He finished his doctoral thesis at the Institute for Theoretical Physics at TUB in 2023. Currently, he is a postdoctoral researcher at the Otto von Guericke University Magdeburg. In addition to research on pattern formation and turbulence in active fluids, Henning has worked on projects concerned with flow properties of liquid crystals and non-Newtonian and viscoelastic active materials. His research interests include nonlinear dynamics and pattern formation observed in environmental and biological systems, continuum-theoretical modeling, fluid dynamics, turbulence and turbulent transport, soft matter and biophysics. Besides his research activities, Henning was the managing director of the Collaborative Research Center 910 (CRC 910, ``Control of self-organizing nonlinear systems: Theoretical methods and concepts of application'') from 2019 to 2022. The CRC 910 brought together mathematicians, physicists and neuroscientists working on the control of nonlinear systems far away from equilibrium and organized multiple interdisciplinary conferences, workshops and other events.
Inhaltsangabe
Introduction.- Theoretical Concepts.- Derivation of a Continuum Theory.- Unconstrained Mesoscale Turbulence.- Reorienting External Fields.- Obstacle Lattices,- Conclusions and Outlook.- Appendix.
