Hydrodynamic interactions within fish schools

Fish schooling serves several purposes including predator defense, socialization, and hydrodynamics. At the human level, understanding the hydrodynamic benefits of schooling behavior can help optimize underwater vehicles. Kelly et al. used 2D simulation to investigate high-fidelity fluid analysis within a large fish school.

To mimic fish schooling and swimming, the authors imposed wave kinematics on classical airfoil shapes that represented fish bodies. The airfoil fish were arranged in a basic dense diamond-shaped school. Utilizing high-fidelity numerical simulations, the underlying hydrodynamics of different numbers and groupings were analyzed, along with body-body interactions and wake features.

Data indicated that the arrangements of surrounding fish significantly affected the performance of individual fish. For example, the average swimming efficiency of a 10-fish school was increased by 30% over a single swimmer, and thrust production improved by 114%.

“Interestingly, we found that fish on the edge of the group performed the best, contrary to previous expectations that fish in the middle would be the best swimmers,” said author Haibo Dong.

The enhanced performance of individual fish was attributed to incoming vortex interactions, a block effect, a wall effect occurring at the front, edge, and middle of the school, and an anterior body suction effect occurring at the edge, middle, and back of the school. These groupings proved to be consistent over a range of school arrangements and Reynolds numbers.

“This study sheds light on hydrodynamic interactions in larger fish schools and provides a framework for future research,” said Dong.

Source: “Hydrodynamics of body-body interactions in dense synchronous elongated fish schools,” by John Kelly, Yu Pan, Alec Menzer, and Haibo Dong, Physics of Fluids (2023). The article can be accessed at https://doi.org/10.1063/5.0142950 .