Hydrodynamics of Confined Incipient Active Nematics

The hydrodynamic instabilities inherent in bulk active nematics have been known to organize into large scale coherent flows when guided by confinement. Such long range correlations in the flow is possibly enabled by nematic ordering conveying the effect of confinement to points away from the boundaries.
However, recent experiments on active microtubules in 3D has revealed that confinement in the absence of bulk nematic ordering is sufficient to produce large scale coherent flows. Motivated by these findings, we study a continuum hydrodynamic model of an active filament suspension at densities below the nematic transition, in two and three dimensions. In two dimensions, we find that flow alignment induces weak local ordering and gives rise to net pumping flow states.