Dolphin-inspired skin microvibrations can accelerate swimming

Research on dolphins dates back nearly 90 years to the well-known Gray's Paradox, which proposed that dolphins are capable of swimming at speeds that seemingly exceed their energetic limits. Inspired by microvibrations observed on dolphin skin, longitudinal micro-ultrasonic waves (LMUWs)-a form of dynamic skin vibration-have been shown to significantly reduce drag. This finding motivated our investigation into how these vibrations affect swimming performance under dolphin-like, tail-driven propulsion. In this study, we develop a conceptual two-dimensional computational fluid dynamics model that integrates dynamic skin microvibrations with tail fluke propulsion to systematically explore dolphin swimming dynamics. Two modes of skin vibration are examined: downstream-traveling LMUW (DTLMUW) and upstream-traveling LMUW (UTLMUW). The results demonstrate that DTLMUW enhances net thrust and accelerates swimming, whereas its cessation leads to a speed reduction. Conversely, UTLMUW causes deceleration during application but results in a speed increase once stopped. Therefore, to achieve net acceleration, a longer duration of DTLMUW but a shorter UTLMUW period is most effective. This approach aligns with the optimal interaction between skin motion and the surrounding flow. Moreover, once skin vibrations cease, the forces acting on the model quickly return to their non-vibrating baseline, allowing tail-driven propulsion to maintain the speed gains induced by LMUWs. As the frequency of vibration pulses increases, the acceleration effect becomes cumulative, further boosting overall performance. This study provides new insights into the mechanisms behind dolphins' high-speed swimming and offers valuable guidance for the design and optimization of bioinspired propulsion systems.