Flow Field Around Wall Mounted Circular Cylinders with Strakes

Cylinders fitted with strakes have been studied as a method to suppress vortex shedding and mitigating vortex-induced vibrations. However, the effect strakes have on the horseshoe vortex (HSV) formed on the forebody-bed junction is not fully understood. In this work, a computational fluid dynamic (CFD) study is utilized to further investigate the flow characteristics. A Reynolds averaged Navier–Stokes (RANS) k-ω shear-stress transport (SST) turbulence model was utilized to carry out the numerical study. Simulations of the flow around the cylinder with diameter (D) of 40 mm were carried out. Three models were adopted: a cylinder with no strake and two straked cylinders with strake heights of 0.1D and 0.2D. The straked cylinders were situated such that at the base, the strakes were located at 60° to the approach flow. The cylinder Reynolds number was 28,000 based on the approach flow velocity. The drag coefficient of the no-strake cylinder case agrees well with published results. Wall shear contours along the bottom wall show a larger area of decreased wall shear stress both upstream and downstream of the straked cylinders compared to the bare cylinder. Vorticity contours and visualization of 3D fluid structures show that the HSV is formed further upstream from the pier face in the straked cases than the no-strake cylinder case. It was also observed that the HSV is extended further into the wake region for the straked cylinders. It was also found that the roll-up and subsequent development of the HSV is pushed farther from the base of the cylinder in the straked cases, with the distance increasing with strake height.