Coupling performance of two tandem and side-by-side inverted piezoelectric flags in an oscillating flow

The flow-induced vibration characteristics and energy extraction performance of two flexible inverted piezoelectric flags arranged in tandem and side-by-side configurations in an oscillating flow are studied. An immersed boundary-lattice Boltzmann method is employed for Reynolds number of 100, mass ratio of 2.9 and non-dimensional bending stiffness of 0.26 which correspond to the maximum flapping amplitude for a single inverted flag in a uniform flow. 2D simulations are conducted by varying the ratio R of the frequency of the oscillating flow to the fundamental natural frequency of the flag and the horizontal velocity amplitude (Au) of the flow. Three coupling regimes at Au = 0.5 are identified for both tandem and side-by-side flags: chaotic oscillations regime I (0.1 < R < 1), large periodic and symmetric oscillation regime IIa (1.1 < R < 1.5) and IIb(2.1 < R < 3.0), and small periodic and asymmetric oscillation regime III (1.6 < R < 2). The maximum mean electrical power coefficient CP occurs in regime IIa at R = 1.5 with, alpha (piezo-mechanical coupling parameter) = 0.5, and beta (piezo-electric tuning parameter) = 1.5. CP is 0.1 for a tandem upstream flag, 0.068 for the tandem downstream flag and 0.1 for both side-by-side flags, and is respectively 120%, 300% and 213%, higher than that of the corresponding flag in the uniform flow. This improvement is attributed to the higher flapping angular amplitude (180 degrees), the higher ratio of the flapping frequency of the flags to the oscillating frequency of the flow (virtually constant at 0.5), and constructive vortex interaction in regime IIa. (c) 2023 Elsevier Ltd. All rights reserved.