Wall proximity effects on the flow past cylinder with flexible filament

The response of thin, elastic filament attached to a circular cylinder is numerically investigated under uniform flow at different wall proximities, GD (0.5, 0.6, 0.8, 1, 1.5, 2 and 2.5). The Reynolds number based on the diameter of the cylinder is 200. Numerical simulations were conducted for a range of reduced velocities Ur (3,4,5 and 6), where Ur = U∞fnD which appropriately captures the synchronization range of vortex-induced vibration(VIV) of the structure. Ur is varied by changing the density of the material. The force coefficients, the frequency of shedding/flapping are observed to be the function of GD and Ur. The positive vortices diffuses faster as GD decreases. The skewness in the amplitude attained by the flapping filament on either side of the cylinder causes unsteady shedding of vortices. Filament flaps in frequency that is closer to its natural frequency at higher GD and at lower GD, the frequency of flaps for all Ur is similar. For lower gap ratios, 0.5 and 0.6, the modulations in flapping amplitude is observed. The modulation is predominant as the Ur increases. During the growth and damping phase of the amplitudes in each modulation cycle, the vortex shedding is observed to be oblique towards the wall. The filament flaps in single mode shape. The frequency of the flapping depends on the Ur and GD. The frequency of the flapping is in resonance with shedding frequency.