Hydrokinetic energy conversion using compliant surfaces

Abstract

In this work, consideration is given for a novel technology based on the use of compliant surfaces (membranes) for hydrokinetic energy conversion (HEC) from residual waters where the use of traditional turbines is either not possible or strongly limited. Here, residual waters are understood as waters with a small total pressure difference relative to the surrounding environment that are not suitable to be turbined. Such waters encompass not only domestic or industrial waste water before being discharged into the sewer but also typical flows found in river waterways of small depth or even postturbined water. In summary, the proposed technology is based on the deliberated bifurcation of residual water into two streams separated by a compliant surface or membrane that equalizes the static pressure in both streams and also generates a relative velocity between them. As a result, Taylor instabilities translate into the oscillatory motion of the membrane, which can be transformed into output power. Utilizing linearized flow theory, an analytical expression for the extractable density power is derived. Experiments are carried out for a rectangular membrane, and the data obtained are quantitatively and qualitatively in good agreement with the theoretical model, where it is found that for typical residual water with a velocity of approximately 1.7 m/s, the output power density is on the order of 30 mW/cm2 based on the area of the membrane. Additional research and development is required to arrive at a reliable practical and commercial design.