To perform long endurance military missions, small, unattended sensor packages must generate and harvest power from their surroundings. The experiments described extend our previous studies on the possibility of using piezoelectric polymers as power generation devices. Thin flexible piezoelectric membranes, or "eels," are mounted aft of a rectangular bluff body and are excited by vortex shedding in the wake of the body. This flapping motion generates strain energy in the material that can be converted to electric power and stored in a battery to power small sensors and an acoustic modem. Here we report new experiments on the behavior of multiple eels, stacked vertically behind a single bluff body. Experiments show a range of flow regimes, ranging from poorly coupled motions, where three-dimensionality in the vortex shedding is important, to an optimally coupled state, where the membranes oscillate at the natural frequency of the undisturbed wake. The effects of membrane length are also studied.


To power small, unattended sensors during long endurance missions, it is necessary to have a renewable energy source. The aim of the current work is to develop a novel small-scale generator capable of extracting up to one watt of power from the flow in ocean currents, streams and pipes. In order to accomplish this goal, an energy-harvesting eel has been constructed from piezoelectric materials. The energy-harvesting eel is designed to extract energy from the wake of a bluff body in an ocean current (see figure 1). The basic configuration is a leading bluff body trailed by a thin flexible piezoelectric eel. The bluff body generates vortices which excite a flapping motion of the eel. The eel deformation results in strain of the piezoelectric membrane, which in turn generates a voltage across the material.

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