Large eddy simulation of flow around wavy cylinders at a subcritical Reynolds number

The cross-flow around wavy cylinders of wavelength ratios λ/Dm from 1.136 to 3.333 are investigated at Re = 3000 using large eddy simulation (LES). The mean flow field and the near wake flow structures are presented and compared with those of a circular cylinder at the same Reynolds number. The mean pressure distributions are also calculated. The results show that the mean drag coefficients of the wavy cylinders are less than those of a corresponding circular cylinder due to a longer wake vortex formation length generated by the wavy cylinders. For a subcritical Reynolds number of 3000, a maximum drag coefficient reduction of up to 18% compared with a circular cylinder is obtained corresponding to an optimal wavelength ratio of λ/Dm around 1.9 and an amplitude ratio a/Dm of 0.152. The fluctuating lift coefficients of the wavy cylinders are also greatly reduced or even suppressed. These kinds of wavy surfaces lead to the formation of three-dimensional free shear layers which are more stable than purely two-dimensional free shear layers. Such free shear layers will only roll up into mature vortices at further downstream positions. This significantly modified the near wake structures and the pressure distribution around the cylinder. It was found that the wave amplitude to wavelength ratio a/λ plays an essential role in determining the 3D vortex structure behind the wavy cylinders which has a significant effect on the reduction of the fluctuating lift and suppression of flow-induced vibration.