Abstract
While cilia are generally found in viscosity-dominated regimes, those of a comb jelly, the longest motile cilia in nature, are used for propulsion and feeding in inertia-dominated flows. Motivated by the effective fluid transport of cilia at relatively high Reynolds number, the characteristics of vortex formation and fluid transport are investigated numerically for a simple two-dimensional model of rigid plates in Re = O(10 − 102). The small plates oscillate symmetrically on both walls of a channel. Under some conditions, the vortical structures generated by the plates become asymmetric notably with respect to the channel midline. In relatively narrow channels, the interaction of counter-rotating vortices shed directly from the plates near the midline causes symmetry breaking, and thus the mixing of fluid particles across the midline is enhanced greatly. Meanwhile, in relatively wide channels, the diffused weak vortices that persist after previous strokes become asymmetric first. When the number of oscillating plates on each wall increases, the vortex generated by a plate is confined between two plates, and it is annihilated by the counter-rotating vortex generated by a neighbor plate during stroke reversal, thereby keeping them from propagating toward the midline. This collective motion of multiple plates hinders the vortices from undergoing symmetry breaking even at the relatively high Reynolds number of Re = 200, and mixing is suppressed accordingly.
Highlights
Cilia are hairy structures that are commonly found in various biological systems
Den Toonder et al.9 showed that artificial cilia can generate strong flow and induce effective mixing in microfluidic channels, Fahrni, Prins, and van Ijzendoorn10 demonstrated that systems of artificial cilia can generate rotational and translational fluid motion in a microfluidic chamber, and Hussong et al.12 succeeded in producing fluid transport in a closed micro-channel using magnetically actuated artificial cilia
Motivated by biological cilia in the mouth of the comb jelly and artificial cilia in microfluidic applications, we model our fluid domain as a channel whose upper and lower boundaries are walls and whose left and right boundaries are pressure outlets [Fig. 1(c)]
Summary
Cilia are hairy structures that are commonly found in various biological systems. By their movement, motile cilia can capture prey or generate flow for swimming. As well as hydrodynamic studies, many cilia-inspired microfluidic applications have been suggested because artificial cilia are a promising means of achieving fluid transport and mixing.. Mounted in a channel or a mixer, artificial cilia can generate fluid transport and mixing. Den Toonder et al. showed that artificial cilia can generate strong flow and induce effective mixing in microfluidic channels, Fahrni, Prins, and van Ijzendoorn demonstrated that systems of artificial cilia can generate rotational and translational fluid motion in a microfluidic chamber, and Hussong et al. succeeded in producing fluid transport in a closed micro-channel using magnetically actuated artificial cilia
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