Initial release styles have limited effects on the hydrodynamic dynamics of a self-propelled fin in the unsteady wakes

TL;DR

This study investigates how initial release styles influence the hydrodynamics of a self-propelled fin in unsteady wakes, finding that in realistic conditions, initial release styles have limited impact on fish-like swimming behavior.

Contribution

The paper demonstrates that initial release styles have minimal effects on the hydrodynamics of self-propelled fins in unsteady wakes, especially when starting from fully developed flow conditions.

Findings

Fins are more resilient to initial perturbations in schooling scenarios.

Fully developed wake conditions lead to consistent fin behavior regardless of initial release style.

Initial release styles have limited influence in natural unsteady flow environments.

Abstract

Living fish may suddenly encounter upstream obstacles, join the queue of the fish schooling, or detect upstream flow in advance, resulting in interactions with environmental vortices that can be abrupt or develop gradually from an initial state. The impact of initial conditions on fish swimming behavior in unsteady upstream vortices remains an open question. This study employs a self-propelled flexible fin model, the immersed boundary method, and direct simulation to analyze the hydrodynamics and locomotion of fish swimming behind a bluff cylinder and within the schooling, under different initial gaps and release styles. Additionally, the above tests were conducted with both quiescent flow fields and fully developed unsteady flows as initial conditions. The results indicate that schooling self-propelled fins are more resilient to initial perturbations compared to fins swimming behind a bluff body. More importantly, when simulations begin with a fully developed wake pattern, which better reflects natural environments, the characteristics of the self-propelled fins remain consistent regardless of the initial release styles. Therefore, from a hydrodynamic perspective, we conclude that initial release styles have limited effects on living fish in unsteady wakes.