Abstract The energetic consequences of swimming within a neighboring fish’s vortex street remain a central question in collective locomotion. Recent flume experiments in which a flapping hydrofoil generated a biomimetic wake demonstrated that a trout can station-keep behind the foil while displaying kinematics markedly different from those used in uniform flow. To examine the underlying hydrodynamics, we accurately replicate the fish-foil system by first reproducing the experimentally recorded motions using a joint-based kinematic reconstruction method, and then we simulate the fluid dynamics with three-dimensional (3D) computational fluid dynamics (CFD). A companion simulation without the foil is also conducted to isolate wake effects. Relative to uniform-flow swimming, the presence of the foil wake reduces the trout’s cycle-averaged hydrodynamic power expenditure by 11.4+/-0.0003%, a benefit that arises because vortex columns shed by the foil create coherent negative-pressure corridors along the fish’s lateral surface. Power reduction is realized when the trout’s long-wavelength body wave remains phase-locked with the downstream advection of these vortex structures, enabling the fish to harvest pressure-induced thrust while minimizing added-mass losses. These findings provide a mechanistic explanation for wake exploitation in schooling fish, establish phase synchrony as a key control parameter for hydrodynamic benefit, and offer design guidelines for paired biomimetic underwater vehicles that seek to emulate schooling to improve propulsive efficiency.
Guo et al. (2025) studied this question.