A numerical study on the hydrodynamics of a swimming crocodile model.

This article focuses on investigating the propulsion mechanisms of a cruising crocodile (Crocodylus siamensis) through three-dimensional computational fluid dynamics (CFD) simulations. Using a simplified 3D model based on a juvenile crocodile and employing the shear-stress transport (SST) k–ω turbulence model, the study examines how undulation parameters—specifically amplitude and frequency—affect hydrodynamic forces, power consumption, pressure distributions, and wake flow structures at a cruising speed corresponding to a Reynolds number of approximately 9.95 × 10^5. Results reveal that the mean axial force and power coefficients increase with undulation frequency and amplitude, scaling well with the Strouhal number (St), with a critical St of about 0.5 marking the transition from drag- to thrust-dominated swimming. Distinct wake patterns—ranging from hairpin-like vortices to staggered vortex rings and complex entangled vortices—are associated with different swimming modes, providing insights relevant to both biological understanding and the design of biomimetic amphibious robots.