Impact of surface roughness on energy harvesting: Comparative study of smooth and rough cylinder

Abstract

The world is moving towards renewable energy resources as an efficient way of energy harvesting because of the depleting energy resources and the low installation cost. One of the sources of energy harvesting is the hydel source which takes advantage of the flow energy of water in oceans to generate energy. This experimental study aims to investigate the effect of surface roughness of cylindrical cylinders on the energy harvested by piezoelectric eels using low-speed water tunnels. The piezoelectric eel is placed in the wake of the cylinders with varying roughness. The experiments are performed for four different roughness (Ks/D) of 8.8 x10-5, 1.51 x 10-4, 3.62 x 10-4 and 5.08 x 10-4 of the cylinder. For each roughness, the distance between the center of the cylinder and the center of the eel is changed both in x- and y-direction. The flapping frequency, dimensionless amplitude, and optimal power of the rough cylinders are analyzed and compared with that of the smooth cylinder. The highest power is obtained on the eel at the optimal point. By increasing the surface roughness of the bluff body, the lock-in region decreases and as a result, the harvested power from that bluff body wake is reduced. Moreover, the power also decreases with increasing the distance between the cylinder and eel both in x- and y-direction.