Enhanced velocity fluctuations in interacting swimmer suspensions

Abstract

Abstract

Concentration banding instability of a sheared bacterial suspension

“…It should be noted that the kinetic equation (2.1), that lies at the heart of this framework, does not therefore include either direct hydrodynamic or steric interactions between the swimming bacteria. While recent efforts have analysed pairwise hydrodynamic interactions in the Stokes-Smoluchowski framework, this lies beyond the scope of the current effort (Stenhammar et al 2017;Nambiar, Garg & Subramanian 2019a).…”

The hydrodynamics of slender swimmers near deformable interfaces

“…( 9) will be O(ln κ) −2 rather than leading order, and hence asymptotically smaller. A similar argument has been used recently to consider the tracer diffusivity and the velocity variance in a suspension of interacting slender swimmers in bulk [52]. Thus, to a leading order in (ln κ) −1 , one can simplify Eq.…”

“…(1a), f α , represents the forcing due to the slender swimmer and characterizes a line distribution of Stokeslets along the axial coordinate of the swimmer. For a fore-and aft-symmetric swimmer, which disturbs in the surrounding fluid medium as it moves, one may write f α as [51,52]:…”

“…Here, we consider the motion of a slender microswimmer moving in the proximity to a deformable interface that separates two Newtonian fluid regions of different viscosities. By modulating the distribution of forces along the swimmer length, we are able to model both pusher-and puller-type swimmers [51,52], hereafter referred to as pushers and pullers, respectively. Importantly, using slenderbody theory enables us to resolve the hydrodynamics in regions of order the swimmer size L owing to the weak inverse logarithmic scaling of the disturbance flow field in κ [53].…”

Density Fluctuations and Energy Spectra of 3D Bacterial Suspensions

“…This finding is in direct contrast to GNF of 2D active systems, where GNF diminishes with decreasing particle concentrations and disappears for lowconcentration samples [7][8][9][10][11]14]. Kinetic theories have predicted that, due to the long-range hydrodynamic interactions, pusher-type microswimmers in 3D active suspensions show strong spatial and temporal correlations at low concentrations well below the transition concentration to active turbulence [48,49]. Although the theories only discussed the effect of the correlation on the enhanced diffusion of passive tracers and velocity fluctuations in dilute suspensions, our experiments show that such a correlation also manifests as GNF at small length scales in low-concentration bacterial suspensions.…”