Numerical simulations on the flow past a flexible filament with two fixed ends at a low Reynolds number

Abstract

This study explores an interesting fluid-structure interaction scenario: the flow past a flexible filament fixed at two ends. The dynamic performance of the filament under various inclination angles was numerically investigated using the immersed boundary method. The motion of the filament in the - space was categorised into three flapping modes and two stationary modes, where is the ratio of filament length to the distance between its two ends. The flow fields for each mode and their transitions were introduced. A more in-depth analysis was carried out for flapping at a large angle (FLA mode), which is widely present in the - space. The maximum width of the time-averaged shape of the filament has been shown to strongly correlate with the flapping frequency. After non-dimensionalising based on, the flapping frequency shows little variation across different and. Moreover, two types of lift variation process were also identified. Finally, the total lift, drag and lift-to-drag ratio of the system were studied. Short filaments, such as those with, were shown to significantly increase lift and the lift-to-drag ratio over a wide range of compared with a rigid plate. Flow field analysis concluded that the increases in pressure difference on both sides of the filament, along with the upper part of the flexible filament having a normal direction closer to the direction, were the primary reasons for the increase in lift and lift-to-drag ratio. This study can provide some guidance for the potential applications of flexible structures.