Introduction

Microswimmer suspensions are a paradigmatic example of active matter, a term that describes non-equilibrium systems whose constituents perform persistent, self-propelled motion. This thesis investigates the spatiotemporal patterns emerging in the flow field of these microswimmer suspensions, with a particular emphasis on a recently observed state denoted as mesoscale turbulence. We aim for a consistent continuum-theoretical description on the basis of coarse-grained order parameter fields such as the effective microswimmer velocity, which enables us to explore the emerging structures and how they might be controlled from the outside. The first chapter of this thesis gives a general introduction to the basic concepts necessary to approach the topic from a physical perspective, starting with a broad overview of active matter and then gradually moving closer to the specifics of microswimmer suspensions and mesoscale turbulence.