Spontaneous Rising of a Whirling-Swimmer Driven by a Bubble

The wind-dispersed seeds can rotate and fall like small vehicles with the help of the wind to obtain a longer propagation distance. Inspired by this, we propose a novel bubble-driven three-bladed whirling-swimmer (WS) to travel in the fluid as a vehicle. Four types of WSs with blade folding angles (φ) ranging from 10 to 60° were designed, and their swimming performance was evaluated. Regardless of the WS shape, the velocity increases linearly with φ, while the angular frequency exhibits an asymptotic value. Further, both the St and rotational energy of the WS peak at 20° ≤ φ ≤ 30° for different WS shapes as well as the vertical force and the hydrodynamic torque were solved from a proposed mechanics model. This folding angle range is unexpectedly consistent with the coning angle during maple samaras' stable falling. The WS lift and drag forces greatly depend on the interaction between the leading-edge vortex and the hub vortex. The results showed that the WS-IV seems to have the highest performance. Our work may shed new light on developing unpowered wireless swimmers of high swimming performance to provide a new way for underwater information collection, information transmission, and enhanced mixing.