Hydrodynamics of ciliary propulsion

A numerical approach is developed to study the effect on a fluid of the regular oscillations of an array of flexible cilia which hinge around points on a wall. The specific application studied concerns the ctenophore Pleurobrachia pileus, a small marine invertebrate of quasi-spherical shape and diameter of the order of the centimeter which swims in water thanks to the rhythmic beating of eight rows of hair-like cilia aligned along its body. Only one row of cilia is studied here, in a three-dimensional setting. The technique presented is general enough to allow its application to a variety of fluid-structure interaction problems. The physical mechanisms of the propulsion are highlighted, by analysing the results of three-dimensional simulations. A parametric study involving natural and non-natural parameters leads to a better understanding of the propulsive characteristics of ctenophores; results show that the specific power expended increases with the increase of the beating frequency of the row of cilia, in agreement with experiments. (C) 2008 Elsevier Ltd. All rights reserved.