Flow-induced vibrations of elastically-mounted C- and D-section cylinders

We numerically study the flow-induced vibration (FIV) response of an elastically-mounted cylinder in two-dimensional coordinates at Reynolds number of 100. In particular, the effects of shape of frontbody and afterbody are systematically investigated by varying the cylinder’s cross-section, keeping the mass ratio of 5 as constant. The following cross-sections are considered — circular, C-section, inverted D-section, D-section, and inverted C-section. We employ an in-house flow solver based on the sharp-interface immersed boundary method and the solver is one-way coupled with a forced harmonic oscillator equation with a single degree of freedom. We explain the FIV characteristics using displacement amplitude, spectral characteristics of displacement and force signals, and wake modes. Considering a circular cylinder as a baseline case, a modification in the shape of the frontbody from convex to flat to concave causes large amplitude vibrations. A D-section cylinder, which corresponds to the flat frontbody, shows a significant increase in the amplitude for a wide range of reduced velocity compared to the circular cylinder, explained by combined Vortex-induced vibration (VIV) galloping response. By contrast, a variation in the shape of the afterbody from convex to flat to concave results in reducing amplitude, implying VIV suppression. The suppression is explained by the reduction of unsteady pressure forcing during vortex shedding on the cylinder. We discuss wake structures and vortex shedding patterns as a function of reduced velocity for the cylinders and explain these signatures in terms of the respective FIV response. The fundamental insights reported here are potentially helpful for structural health monitoring and energy harvesting applications.