Fluid dynamics of cilia on a comb jelly

Cilia are hairy structures in biological systems used to help capture prey or aid in swimming. Inspired by the efficient fluid transport and mixing by the cilia on comb jellies, specifically the inertia-dominant flows of high Reynolds number, Lim et al. investigated vortex formation and fluid transport caused by oscillating rigid plates in a channel.

The researchers simulated the flow of an incompressible fluid in a model domain consisting of two horizontal walls, each with up to five rigid plates which oscillate symmetrically. The resulting fluid motion was then studied.

When the researchers modeled one plate at each boundary, they found that an increase of the system’s Reynolds number – or as the system becomes more prone to hydrodynamic instability – the fluid particles from the two boundaries mix more quickly, breaking the flow symmetries. As vortices from the top and bottom plates meet in the center, they interact and the hydrodynamic flow in the system becomes chaotic.

Surprisingly, when the scientists increased the number of plates at each boundary to five to better model real cilia clusters, they saw a suppression of chaotic behavior, even at high Reynolds numbers. When a vortex is created between the plates, it is quickly annihilated by a counter-rotating vortex as the plates switch the direction of their stroke. With larger numbers of plates, the symmetry remains unbroken and the fluid mixing is not enhanced.

Cilia-inspired biomimetic applications are promising in achieving efficient fluid transport and mixing, but additional work needs to be done to understand their complicated dynamics. Looking ahead, the authors hope to better mimic and understand these systems by modeling flexible plates with asynchronized oscillation.

Source: “Inertia-driven flow symmetry breaking by oscillating plates,” by Daegyu Lim, Mohsen Lahooti, and Daegyoum Kim, AIP Advances (2019). The article can be accessed at https://doi.org/10.1063/1.5122966 .