Fluid-structure interaction of a flexible membrane under movement-induced excitation (MIE), extraneously induced excitation (EIE), and coupled MIE-EIE

This study comprises an extensive analysis of the fluid-structure dynamics of a flapping membrane under three different excitation mechanisms: movement-induced excitation (MIE), extraneously induced excitation (EIE), and coupled MIE-EIE. Using a data acquisition system at 51.2 kHz and a high-speed camera at 1 kHz, the temporal voltage variations and the deformation shapes of the membrane were, respectively, determined. By the analysis of voltage fluctuations, two characteristic frequencies were observed under coupled MIE-EIE, corresponding to the flapping frequency of the membrane under MIE and the shedding frequency of the cylinder wake under EIE. The EIE frequency is four times larger than the MIE frequency, which indicates that four consecutive shedding periods of the cylinder wake occur during one flapping period of the membrane. Then, three distinct flapping behaviors of the membrane were observed with different excitation mechanisms. The flapping dynamics of the membrane exhibit a second-harmonic-order shape with a single neck under MIE, but a first-order shape with a narrow flapping range under EIE. In contrast, the membrane shows a superimposed second-order behavior with a confined flapping amplitude and the backward movement of the single neck position under coupled MIE-EIE. Subsequently, the flow dynamics around the membrane were examined in terms of time-averaged and statistical flow quantities. Finally, using event-driven particle imaging velocimetry measurements, the spatiotemporal evolutions of the high-resolution flow behaviors surrounding the flapping membrane were determined. The flow dynamics behind the membrane shows that the fluid flow with high turbulence always bifurcates toward both sides under MIE or distributes in the central region under EIE, whereas under the coupled excitation it spreads evenly and widely. This study will offer an important reference for improving the performance of fluid-induced membrane vibrations in industry applications.