Hydrodynamic Scaling in Anguilliform and Carangiform Propulsion

This study explores the scaling of pressure and vorticity in anguilliform and carangiform swimming using self-propelled, wall-resolved large-eddy simulations of a lamprey and a mackerel. In anguilliform swimmers, pressure scales with fluid acceleration (local and convective), indicating propulsion dominated by unsteady added mass effects. In carangiform swimmers, pressure also scales with angle of attack, especially near the posterior body. Vorticity in the boundary layer initially follows body rotation at low speeds (scaling with Strouhal number) but is dominated by shear at high speeds (scaling with √Re). A counterintuitive drop in pressure with increased swimming speed is linked to reductions in both acceleration and angle of attack. These findings show that efficient swimming requires minimizing pressure differences—just enough to overcome viscous drag—while reducing energy loss. The study also shows that traveling wave kinematics enhance thrust generation and improve efficiency, reinforcing their evolutionary advantage in aquatic locomotion.