Propulsion through asymmetry: Examining flow-structure interactions of Ctenophore appendages with asymmetric stiffness

Ctenophores (or comb jellies) utilize multiple rows of flexible appendages known as ctenes for propulsion. Their unique propulsion mechanism relies on the metachronal beating of these ctenes. Unlike a rigid oar that moves back and forth in water, these ctenes exhibit an asymmetrical beating pattern that allows ctenophores to move effectively through their aquatic environments. The ctenes display a difference in flexibility during the power stroke and the recovery stroke. The ctenes are stiffer during the power stroke, enabling them to generate a stronger propulsive force. During the recovery stroke, the ctenes become more flexible, which reduces drag, allowing the ctenophore to maintain its forward momentum. This study delves into the intriguing mechanics of ctenophore propulsion, focusing on the role of asymmetric stiffness in effective propulsion. For this, we combined an existing in-house immersed-boundary-method-based flow solver with a nonlinear finite-element solid-mechanics solver for three-dimensional fluid-structure interaction (FSI) simulations. The FSI is achieved through a two-way coupling method. This study aims to provide valuable insights for bio-inspired engineering, particularly for designing underwater robots, indicating the potential to enhance propulsion efficiency through flexible and asymmetrical structures.