Modulation of flexible filaments dynamics due to attachment angle relative to the flow

This paper describes experiments carried out in a wind tunnel with three flexible silicone filaments (length to diameter ratio L/D = 50, 100, 150) hanging in crossflow in the range of reduced velocities of 7 < U* < 150 and at various attachment angles (0 ≤ α ≤ 90°) with respect to the flow direction. At low reduced velocities, due to the negligible bending stiffness, the filaments were statically reconfigured but remained mostly rectilinear along their lengths, except for the relatively small bent portion of the filaments close to the upstream fixed end. As the reduced velocity was further increased the filaments started vibrating, but in certain cases large-amplitude flapping motions were observed. Despite of the negligible role of the attachment angle at the fixed end on the static reconfiguration of the filaments, it was found that it plays a crucial role on the dynamics of the flapping motions, as it determines whether the filaments exhibit large-amplitude limit-cycle oscillation dynamics or noisy small-amplitude vibrations.