2025/03/31 by Kumar, Sushrut, McHenry, Matthew J., Seo, Jung-Hee +1
#Biological Physics (physics.bio-ph) #FOS: Physical sciences #Fluid Dynamics (physics.flu-dyn)
paper · doi:10.48550/arxiv.2503.23652
Fish swim with flexible fins that stand in stark contrast to the rigid propulsors of engineered vehicles, though it is unclear whether this flexibility endows animals with a performance advantage. Using numerical simulations of the mechanics of flow-structure interaction (FSI), we found that flexible fins are up to 70% more efficient than rigid fins. By comparing the dynamics of FSI, we find that the power requirements of rigid fins can be largely attributed to their propensity to generate high-magnitude lateral forces. In contrast, flexible fins achieve high efficiency by a mechanism known as local-force redirection where deformations orient fluid forces in fore-aft and dorso-ventral directions to reduce the power demand of generating lateral forces. These deformations occur at moments in the tail-beat cycle when large velocities and pressure differentials are generated due to the mechanics of the fin and surrounding flow.