Multi-frequency vortex-induced vibrations of a long tensioned beam in linear and exponential shear flows

Rémi Bourguet (1) , George E. Karniadakis (2) , Michael S. Triantafyllou (3)

1 IMFT - Institut de mécanique des fluides de Toulouse
2 Brown University
3 MIT - Massachusetts Institute of Technology

The multi-frequency vortex-induced vibrations of a cylindrical tensioned beam of aspect ratio 200, free to move in the in-line and cross-flow directions within first a linearly and then an exponentially sheared current are investigated by means of direct numerical simulation, at a Reynolds number equal to 330. The shape of the inflow profile impacts the spectral content of the mixed standing traveling wave structural responses: narrowband vibrations are excited within the lock-in area, which is limited to a single region lying in the high flow velocity zone, for the linear shear case; in contrast, the lock-in condition occurs at several spanwise locations in the exponential shear case, resulting in broadband responses, containing a wide range of excited frequencies and spatial wavenumbers. The broadband in-line and cross-flow vibrations occurring for the exponential shear current have a phase difference that lies within a specific range along the entire span; this differs from the phase drift noted for narrowband responses in linear shear flow. Lower vibration amplitudes, time-averaged and fluctuating in-line force coefficients are observed for the exponential shear current. The cross-flow force coefficient has comparable magnitude for both inflow profiles along the span, except in zones where the broadband vibrations are under the lock-in condition but not the narrowband ones. As in the narrowband case, the fluid forces associated with the broadband responses are dominated by high frequencies related to high-wavenumber vibration components. Considerable variability of the effective added mass coefficients along the span is noted in both cases.

Mots clés: Vortex-induced vibrations; Narrowband and broadband multi-frequency responses; Lock-in in shear flow; Tensioned beam; Direct numerical simulation

Domaines: Mécanique des fluides [physics.class-ph]; Mécanique des structures [physics.class-ph]

Rémi Bourguet, George E. Karniadakis, Michael S. Triantafyllou. Multi-frequency vortex-induced vibrations of a long tensioned beam in linear and exponential shear flows. Journal of Fluids and Structures, 2013, 41, pp.33-42. ⟨10.1016/j.jfluidstructs.2012.07.007⟩. ⟨hal-03523318⟩