Study of vibration modes and strain distribution of a flow energy harvester in the wake region of different bluff bodies

Abstract

This paper aims to analyze mode shapes and corresponding strain distribution in a two-dimensional plane structure exhibiting flow-induced vibration in the wake field of four different upstream bluff bodies such as cylinder, square, triangle, and D-shape. This research is important from the point of view of flow-induced piezoelectric energy harvesting; wherein, induced strain in the structure is directly related to the amount of energy generated. Mainly, all investigations are carried out at low Reynolds number ( Re = 200); however, to widen the scope of the work, other Reynolds numbers are also considered ( Re = 300, 500, and 750 ). The results obtained indicated that the plane structure vibrates in different mode shapes under different wake fields. The square section dominantly gives rise to the fundamental mode vibration, whereas, cylinder, D-shape, and triangular bluff body induce vibration in a mix of fundamental and higher bending modes. Analysis of the corresponding flow regime shows that the position of reattachment point of the downstream shear layer plays an important role in the realization of different vibration modes. The strain distribution under different cases revealed that the wake of a cylindrical bluff body produces highest peak strain, and D-shape bluff body results in highest cumulative strain. From the aspect of energy harvesting, a quantitative comparison of strain-induced and per second charge generation have indicated that for an equivalent flow condition, the D-shape will produce higher energy per unit time than the cases of a square, cylinder, and triangular cross-sections.