PASSIVE AND ACTIVE FLOW CONTROL BY SWIMMING FISHES AND MAMMALS

TLDR

Animals manipulate flow around their bodies and appendages both passively and actively, with passive mechanisms relying on structural and morphological features such as humpback whale tubercles and riblets. The study investigates the mechanisms animals use to control flow and enhance hydrodynamic performance. Active flow control is achieved by muscularly generated wake structures or fin stiffening to counter external loads. Fish actively control fin curvature, displacement, and area, and their tail vortex wakes differ between eel‑like species and those with a discrete body narrowing, with 3‑D effects likely influencing wake structure.

Abstract

What mechanisms of flow control do animals use to enhance hydrodynamic performance? Animals are capable of manipulating flow around the body and appendages both passively and actively. Passive mechanisms rely on structural and morphological components of the body (i.e., humpback whale tubercles, riblets). Active flow control mechanisms use appendage or body musculature to directly generate wake flow structures or stiffen fins against external hydrodynamic loads. Fish can actively control fin curvature, displacement, and area. The vortex wake shed by the tail differs between eel-like fishes and fishes with a discrete narrowing of the body in front of the tail, and three-dimensional effects may play a major role in determining wake structure in most fishes.