Mixing in Arrays of Coupled Villi-Like Actuators

This paper is concerned with computational modelling of fluid mixing by arrays of actuators. We are motivated by intestinal villi, small finger-like projections that densely line the small intestine that play a key role in digestion, by providing the site of absorption of nutrients into the bloodstream, and whose behaviour is believed to function as part of a coordinated peripheral strategy to enhance digestion via local mixing. Despite promising applications for artificial villi, such as next-generation Microbial Fuel Cells (MFCs) and swimming robots, the lack of knowledge of mixing by villi-like structures across inertial scales poses a challenge for the development of artificial prototypes. Here, we present an analysis of fluid mixing by arrays of oscillating two-dimensional villi-like actuators. We construct a two-dimensional immersed boundary method solver to solve the Navier-Stokes equations, across the transitional regime. By varying the phase-difference between adjacent villi, we show that local coupling strongly affects peripheral flow conditions, resulting in substantial differences in mixing and transport as the forcing increases.Our results provide a mapping for a range of behaviours that can be achieved through coordinated active motions of villi-like structures and is useful for informing biology and the design of other future robotics and fluidic-control systems