Scaling the propulsive performance of heaving flexible panels

Abstract

We present an experimental investigation of flexible panels actuated with heave oscillations at their leading edge. Results are presented from kinematic video analysis, particle image velocimetry, and direct force measurements. Both the trailing edge amplitude and the mode shapes of the panel are found to scale with dimensionless parameters originating from the Euler–Bernoulli beam equation. The time-averaged net thrust increases with heaving frequency, but experiences localized boosts near resonant frequencies where the trailing edge amplitude is maximized. These boosts correspond to local maxima in the propulsive efficiency. For a constant heave amplitude, the time-averaged net thrust coefficient is shown to be a function of Strouhal number over a wide range of conditions. It appears, therefore, that self-propelled swimming (zero net thrust) only occurs over a small range of Strouhal numbers. Under these near-constant Strouhal number conditions, the propulsive economy increases with higher flexibilities and slower swimming speeds.

Gait and speed selection in slender inertial swimmers

“…2C. These steady-state results are consistent with experiments and transient computations of thrust production in a foil that is excited at its tip (11,22,23). Indeed, the fundamental resonance frequencies of the passive sheet activated at its leading edge and those of the fully actuated swimmer are coincident, as shown in in Fig.…”

“…To further clarify this observation, we consider the case of a biomimetic swimmer: a flexible sheet that is forced at its leading edge via an oscillating torque (11,22,23). In our model this corresponds to letting m a = ða=2ÞsinðωτÞδ k ½x , where δ k ½ · is the Kronecker delta.…”

“…Indeed, when a dead fish is dragged through water it flutters and moves in a manner reminiscent of a live, swimming fish (23). Similarly, a passive flexible foil whose tip is subject to oscillations can generate thrust (11,22). These observations suggest that the nervous system can work in close conjunction with and profits from elastohydrodynamic effects.…”

“…The hydrodynamics of swimming has been the subject of a variety of studies for more than half a century from experimental (3-6), theoretical (7)(8)(9)(10)(11), and computational (12)(13)(14)(15)(16)(17)(18)(19) perspectives. Recently there has been growing interest in integrating these physical approaches with neurobiological models using coupled neuromechanical simulations (20) and biomimetic devices (21,22) to study developmental and evolutionary aspects of the problem. Indeed, when a dead fish is dragged through water it flutters and moves in a manner reminiscent of a live, swimming fish (23).…”

A fast Chebyshev method for simulating flexible-wing propulsion

“…Recently, great theoretical, experimental, and computational efforts have been directed towards advancing our understanding of flexible-wing propulsion [33,2,4,84,88,79,19,57,89,72]. These studies have demonstrated that flexibility can drastically improve propulsive performance, especially when a wing or fin is driven near resonance [51,50,21,54,69].…”