Active-particle suspensions: Inertial particles in turbulence to micro-swimmers

Martin Maxey

Brown University, Providence, USA

Active suspensions range from the dynamics of finite-size inertial particles in turbulence to the collective motion of biological and artificial micro-swimmers. Inertial features in turbulent liquid flows are closely linked to finite-size and finite-volume effects. Buoyant particles tend to accumulate locally in vortices while dense particles are biased to zones of high strain-rate. These processes are limited by particle size, particle interactions and an effective particle pressure. The particles also create an effective viscous stress that modifies the inertial energy transfer between scales. Spherical particles represent the simplest form of suspension and richer dynamics are seen for the active swimming motion of bacteria or zooplankton even in simple flows. These topics will be discussed based on recent numerical simulations and in the context of available experimental results.