Influence of Aspect Ratio of Sheets on Flutter Characteristics

Abstract Thin flexible sheets are used in numerous engineering applications, e. g. polarizing films and papers. In their manufacturing processes, the sheets subjected to high-speed fluid flow. Then, the flutter is caused to the sheet due to the interaction of fluid flow and sheet motion. The violent fluttering motion can cause serious damage to the sheet such as winkles and scattering of coated liquid on the sheet. Thus, a deeper understanding of flutter characteristics is crucial to avoid the flutter. In this study, the influence of an aspect ratio (ratio of chord and span length) of sheet, that is, three-dimensional effect on flutter characteristics (flutter velocity and amplitude) is investigated by a nonlinear analysis. A nonlinear fluid-structure interaction model is developed. The sheet is modeled as a cantilevered two-dimensional beam. The nonlinearity due to large deformation is considered in the modeling. Moreover, the fluid force acting on the sheet surface is calculated by the three-dimensional vortex-lattice method based on potential flow to consider span-wise distribution of the fluid force. Flutter amplitudes (amplitudes under limit cycle oscillation) are calculated varying the flow velocity. Following results are obtained in the present study: (1) The flutter amplitudes become large as the aspect ratio of the sheet increases. (2) The flutter velocity tends to decrease as the aspect ratio of the sheet increases.