Hydrodynamic investigation of stingray self-burial and concealment behavior on seabed sediments

Stingrays rapidly self-bury by vigorously flapping their pectoral fins to stir up seabed sediments, enabling both effective predation and predator avoidance. Inspired by this behavior, this study develops a two-dimensional fluid–particle coupled model of the stingray self-burial process. An Euler–Euler multiphase flow framework is adopted to describe the interactions within the water–sediment mixture, and the effects of flapping frequency (0.2–1.8) and flapping cycles (1–10) on self-burial performance are quantitatively analyzed. Coverage ratio, average burial thickness, input power, and energy efficiency are employed as evaluation metrics to systematically reveal how motion parameters modulate vortex structures, flow-field scales, and sediment transport mechanisms. Results indicate that the core mechanism of self-burial lies in the tip vortex (TV) generated during the upstroke of the pectoral fin, which evolves into a sediment jet directed toward the dorsal surface during the downstroke. This jet drives the sediment through a periodic “entrainment–dispersal” fluidization process, ultimately depositing sand onto the stingray's back. High-frequency flapping substantially enhances vorticity and sediment transport capacity, achieving effective burial within only 2–3 cycles with higher efficiency. Meanwhile, there is an optimal range for the number of flapping cycles; excessive flapping entrains more sediment but shifts the deposition zone away from the body surface. Overall, this study elucidates the mechanism of the fluid–sediment coupling of stingray self-burial and provides theoretical insights for the design of biomimetic self-burying underwater robots.