Hydrodynamics of active bacteria suspensions in a Hele-shaw cell*

Hydrodynamic dispersion between two miscible passive fluids in a Hele-Shaw cell have been studied extensively both theoretically and experimentally over the years. However, the dispersion of active bacteria suspensions in shear flows is still poorly understood although it is a key for a wide range of applications in the fields of biology, ecology, environmental engineering, etc. This  present work focuses on studying the dispersion of an active bacteria suspension subject to flow and displacing a miscible passive fluid in a Hele-Shaw cell. We monitor the spatio-temporal longitudinal concentration profiles of the fluorescent bacteria suspension for multiple initial cell concentrations, degrees of confinement and imposed average flow velocities. We observe an increased dispersivity of an active bacteria suspension when compared to that predicted by the classical Taylor dispersion model for a passive point particle suspension. We believe that this study would enhance our understanding of active dispersion of bacteria through porous media, on surfaces etc. where shear flows are ubiquitous.