Computational analysis of hydrodynamic interactions in a high-density fish school

Abstract

Numerical simulations are employed to study hydrodynamic interactions between two-dimensional fish-like bodies under a traveling wavy lateral motion in high-density diamond-shaped fish schools. This study focuses on two different streamwise spacings, a dense school with 0.4 body length (BL) spacing and a sparse school with 2.0 BL spacing, respectively. An immersed-boundary-method-based incompressible Navier–Strokes flow solver is then employed to quantitatively simulate the resulting flow patterns and associated propulsive performance of the schools. The results suggest that a fish in the dense school achieves higher thrust production and higher propulsive efficiency than that in the sparse school due to a strong wall effect from neighboring fishes. In addition, results from changing the lateral spacing in the dense school have shown that the wall effect is enhanced as the lateral spacing decreases. Flow analyses have shown that the wake pattern of the fish swimming diagonally behind the leading fish in a dense diamond-shaped school transfers from 2S to 2P when the lateral spacing is smaller than 0.6 BL. As a result, an angled jet is produced behind the school and brings more momentum downstream. At the same time, the appearance of the trailing fish results in a stronger pressure region behind the leading fish and leads to a higher hydrodynamic performance of the leading fish in the dense school. The insights revealed from this study will contribute to understanding physical mechanisms in fish schools and providing a new swimming strategy for bio-inspired underwater swarm robots.

Bio-Inspired Propulsion: Towards Understanding the Role of Pectoral Fin Kinematics in Manta-like Swimming

“…[ 27 , 30 , 31 ]. Recent applications of the solver used in the current study for biologically-inspired swimming used in the current study include inline flapping foils, flapping foil geometry optimization, dense fish schools, and Crevalle jackfish swimming [ 32 , 33 , 34 , 35 ]. CFD is a powerful tool for studying fluid-related biological phenomena from microorganisms to larger flying and swimming animals (as with the current study).…”

The role of hydrodynamics in collective motions of fish schools and bioinspired underwater robots

“…PIV has also been applied to multiple interacting hydrofoils (figure 3d) [28,45,61,62]. Numerically, researchers have used methods such as direct numerical simulations with immersed boundaries (figure 3e) [27,44,56,66,67,[77][78][79], multi-particle collision dynamics model [57], and potential flow based solvers [50,80]. However, most existing simulations prescribe the movements of the fish bodies, and the force balance around a fish is not always strictly enforced.…”

Learning to school in dense configurations with multi-agent deep reinforcement learning

“…However, the accuracy of live fish experiments is still in debate since the behavior and energetic cost of a live fish may be influenced by social and psychological factors [14]. A variety of experiments and numerical simulations on the flapping foils and flexible bodies also support this hypothesis, since enhanced thrust or efficiency are observed in different arrangements [15][16][17][18][19][20][21][22][23][24][25]. However, the performance advantage is not evenly obtained by each individual.…”