Wall effects on the self-propulsion of a 3D zebrafish

Based on the finite volume method, this paper systematically investigates the hydrodynamic performance and wake evolution characteristics of a biomimetic zebrafish at different near-wall distances D * and tail-beat amplitudes A * . The results indicate that while swimming near a wall can achieve higher speed, it comes at the cost of efficiency: as D * decreases, the cruising speed and the input power increase, and the efficiency is reduced. The wall effect is particularly significant when D * ≤ 0.7 and is amplified with increasing tail-beat amplitude. When swimming close to the wall, the fish body experiences an attractive force directed toward the wall. To maintain a constant near-wall distance, a yaw angle adjustment is needed, and this angle increases with increasing tail-beat amplitude. Wake analysis reveals that near the wall, both the circulation strength and the radius of the tail vortex ring increase. Although vortex-ring expansion tends to weaken the induced backward jet, the increase in circulation strength is more pronounced, resulting in an increased Γ / R ratio, which is consistent with the observed increase in swimming speed. This study elucidates the coupling mechanism of the effects of the near-wall distance and tail-beat amplitude on the wall, providing insights for understanding the dynamic characteristics of biomimetic fish swimming in proximity to a wall.