Numerical investigations on flow-induced vibration of elastically mounted cylinders in equi-triangular arrangement

The present study is a two-dimensional numerical investigation of flow-induced vibration (FIV) and energy harvesting from three identical circular cylinders positioned in an equi-triangular arrangement. The cylinders are allowed to move only in the transverse direction. Computations are carried out at a low value of Reynolds number (Re = 150), with a mass ratio of 2 and a damping ratio (ζ) of 0.01, over a range of reduced velocity (Ur) from 1 to 15. To examine the effect of angle of orientation, five different angles of flow incidence, θ = 0°, 45°, 90°, 135°, and 180°, are considered. The open source software OpenFOAM v2312 (open field operation and manipulation) has been used to solve the governing equations of fluid flow and cylinder motion. The displacement amplitude, frequency response, phase difference, and wake pattern are analyzed to characterize the FIV responses of all three cylinders. In the equi-traingular arrangement, wake-induced vibrations generally occur with high amplitude for the cylinder that is located in the wake of others. The dynamic response is further analyzed using time series, phase portraits and Poincare maps. Flow-induced forces are quantified through the mean drag and root mean square lift coefficients that are found to depend on the orientation of the equi-triangular arrangement. The nonlinear and time-varying characteristics of wake are investigated using Hilbert–Huang transform. The presence of intra- and inter-wave components in the Hilbert spectra reveals nonlinear interactions from fluid–structure coupling in the three-cylinder arrangement. In essence, this study aims to identify the incidence angle corresponding to maximum energy extraction from the elastically mounted arrangement. Moreover, a comparison of different angles of incidence shows that θ = 90° is the best choice for energy harvesting, followed by 45° and 0°.