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A self-propelling clapping body
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DOI：10.1017/jfm.2023.657.png)
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摘要
En 中文
We report an experimental study of the motion of a clapping body consisting of two flat plates pivoted at the leading edge by a torsion spring. Clapping motion and forward propulsion of the body are initiated by the sudden release of the plates, initially held apart at an angle 2 theta(o). Results are presented for the clapping and forward motions, and for the wake flow field for 24 cases, where depth-to-length ratio (d* = 1.5,1 and 0.5), spring stiffness per unit depth (Kt), body mass (mb) and initial separation angle (2 theta(o) = 45. and 60.) are varied. The body initially accelerates rapidly forward, then slowly retards to nearly zero velocity. Whereas the acceleration phase involves a complex interaction between plate and fluid motions, the retardation phase is simply fluid dynamic drag slowing the body. The wake consists of either a single axis-switching elliptical vortex loop (for d* = 1 and 1.5) or multiple vortex loops (for d* = 0.5). The body motion is nearly independent of d* and most affected by variation in theta(o) and Kt. Using conservation of linear momentum and conversion of spring strain energy into kinetic energy in the fluid and body, we obtain a relation for the translation velocity of the body in terms of the various parameters. Approximately 80% of the initial stored energy is transferred to the fluid, only 20% to the body. The experimentally obtained cost of transport lies between 2 and 8 J kg(-1) m(-1).
Keyword:
swimming/flying
propulsion
vortex dynamics
期刊
IF:
3.9
论文数:
2.0W
被引数:
9.4W
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