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

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.

Automated summary

The study investigated the dynamics of flow-induced flutter of a thin flexible sheet attached to a streamlined support in a low-speed wind tunnel. The behavior of the sheet was found to change from low-amplitude vibration to large-amplitude flutter as wind speed increased, with the initiation of flutter occurring at the second mode limit cycle oscillation (LCO). The role of natural frequencies in the initiation and transition of LCO was highlighted, with PIV results showing accelerated flow over the sheet's surface inducing lift force and forming a large-scale undulating wake.