The dynamics of flow-induced flutter of a thin flexible sheet

Physics of Fluids, Volume 33, Issue 3, March 2021. The dynamics of the flow-induced flutter of a thin flexible sheet attached to a streamlined support was experimentally studied in a low-speed wind tunnel. In this study, both the structural dynamics and the fluid dynamics aspects of flutter were considered. The kinematics of the oscillating sheet was investigated using high-speed imaging and the flowfield was examined using hotwire anemometry and particle image velocimetry (PIV). The small-scale perturbation in the flow over the sheet was found to induce a low-amplitude vibration, which changed to a large-amplitude flutter as the wind speed was increased to a critical value. The initiation of flutter occurs with the second mode limit cycle oscillation (LCO), bypassing the first mode, and changes to third mode LCO at a higher wind speed. Based on the behavior of the sheet, five different regimes are identified and discussed in this paper. The natural frequencies of the sheet were found to have a significant role in the initiation of the LCO and its transition to the higher modes. The PIV results show a highly accelerated flow over the curved surface of the oscillating sheet, which induces a lift force that acts as a driving force. The accelerated flow over the sheet separates at its tail and forms a large-scale undulating wake. In the LCO regimes, any large-scale flow separation over the sheet could not be observed and the flow appears to be attached even at high deflection of the sheet.