Re-entrant self pumping in confined active fluids*

Spontaneous flows in the form of swirls is ubiquitous in biological systems. Such active swirling/turbulent flows self organize into net pumping flows when confined appropriately. Studies on 2D systems suggest that self pumping results when the confinement length scale is smaller than the size of swirls that form spontaneously in the bulk. However, recent experiments have shown that when confined in 3D channels, the emergence of self pumping can be more sensitive to the aspect ratio of the channel than to the size of the channel itself. This is a phenomenon that is unique to 3D and to active fluids. In this talk, I will discuss the origin of this phenomenon using an active hydrodynamic theory.