Resumo:
In the literature, there is scarcity of tests with combined effects of vortex-induced vibrations
(VIV) and rough surface to control drag force behaviour of bluff bodies. In this context, the
present work contributes to the limited studies on the surface roughness effects into the VIV
of a single circular cylinder. The body is forced to oscillate with respect to the free stream.
The numerical approach utilizes a purely Lagrangian description through the Discrete
Vortex Method (DVM) with surface roughness model. Previous works in the literature
have also demonstrated that two-dimensional roughness model is more sensitive than a
single turbulence modeling to capture nonlinear multi-physics phenomenon with a variety
of applications in different engineering areas. In the present results, the dimensionless
oscillation amplitude was fixed at A/D = 0.13 (D is the outer cylinder diameter) and the
body oscillation frequency varied in the range 0.04 ≤ f0 ≤ 0.80. These values were
chosen to compare with experimental data, when possible. Three relative roughness sizes
were chosen, i.e. ε/D = 0.001, 0.0045 and 0.007. The test cases with no roughness
effects, when compared to the experimental data, captured two basic antisymmetrical
modes, namely modes AI and AIV, and also the chaotic mode. The symmetric mode
with coalescence was captured. Those modes indicate that the vortex shedding frequency,
obtained from the time history curve of the drag coefficient force, is synchronized with
the body oscillation frequency at a fixed Reynolds number of 100,000. In certain tests
involving the surface roughness model, a desynchronization between the forced and vortex
shedding frequencies was observed, and significant drag force variations, representing the
main contribution of this study.
