Double wavy geometric disturbance to the bluff body flow at a subcritical Reynolds number

A double wavy (DW) disturbance is newly proposed to obtain the reduction of drag and the fluctuating lift as the passive control for the bluff body flow. The present study expanded the asymmetry of Yoon et al. (2017) and combined two optimum wavelengths in the short and long wavelength ranges of Lam and Lin (2008) and Lin et al. (2016) to realize the DW geometric disturbance. Eventually, the flow past the DW cylinder was computed at the subcritical Reynolds number of 3000 using a large eddy simulation. The DW cylinder achieved the significant reduction of drag and fluctuating lift, compared to those of the smooth cylinder. It is noted that the DW cylinder achieved more reduction of drag and lift fluctuation than the wavy cylinder with the optimum wavelength. The DW cylinder formed the common characteristics of flow which associates with the reduction of drag and the fluctuating lift. The DW cylinder showed the double wavy profile of vortex formation length, which is due to the double wavy distribution of flow. Interestingly, the DW geometry gives a shorter wavy effect on the formation length. Namely, the saddle plane forms a longer formation length than the nodal plane.