Numerical investigations of flow over wavy cylinders at sub-critical Reynolds number

Abstract

Numerical study of three-dimensional unsteady flow behind the double wavy (DW), singe wavy (SW), and smooth circular (SC) cylinders geometry at subcritical Reynolds number (Re = 3.0 x 103) using large-eddy simulations based on the finite volume method are investigated in this study. This study contributes to the understanding of the effects of geometric disturbances as a passive flow control method to reduce the hydro-dynamic forces exerted by the fluid flow on the cylinders. The DW and SW cylinders with spanwise wavelength ratios as lambda/Dm = 3.79 -6.82 and with fixed wave amplitude ratio as a/Dm = 0.152 are investigated and compared with SC cylinder in terms of flow variables such as drag, lift coefficients, Strouhal number, vortex formation length, and vorticity contours of the cylinders. Furthermore, an investigation was also carried out to quantify the differences in the fluid flow properties behind SC and SW cylinders compared to DW cylinders. When compared to the SC and SW cylinders, the findings indicated that the DW cylinder reduces drag and lift coefficients significantly for every lambda/Dm. A maximum reduction in fluid forces is observed at lambda/Dm = 6.06 for DW cylinder; 16.63% and 94.99% reduction in mean drag and lift fluctuations respectively compared to SC cylinder. The DW cylinder also showed a longer vortex formation length than SC and SW cylinders for every lambda/Dm. The flow separation angle and mean streamwise velocity distributions are also investigated and compared between the SC, SW, and DW cylinders. The present study reveals that the geometric surface waviness of the cylinder can be used to minimize force coefficients at a sub-critical flow regime. The obtained conclusions could provide some references to the engineering field for the design stage of slender marine structures.