A self propelling clapping body

TL;DR

This study experimentally investigates the motion and wake flow of a self-propelling clapping body with two plates, analyzing how parameters like spring stiffness and initial angle influence propulsion and vortex formation.

Contribution

It provides a detailed experimental analysis of the dynamics and wake flow of a clapping propulsion system, highlighting the energy transfer mechanisms and effects of geometric and spring parameters.

Findings

Body accelerates rapidly then slows due to fluid drag.

Wake flow varies with body depth, forming different vortex structures.

Approximately 80% of stored energy transfers to fluid.

Abstract

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 $2{\theta}_0$. 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 ($m_b$), and initial separation angle ($2{\theta}_0 $= 45 and 60 deg) are varied. The body motion consists of a rapid forward acceleration to a maximum velocity followed by a slow retardation 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 variations in ${\theta}_0$ 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 $COT$ lies between 2 and 8.