Unsteady Flow past slotted circular cylinders in laminar regime: Effect of slit shapes and Reynolds number

A numerical study of incompressible and unsteady flow past a slotted circular cylinder was carried out in the laminar regime. Three different-shaped slits (converging, diverging, and parallel) were installed symmetrically about the cylinder's horizontal axis. A finite volume-based open-source computational toolbox, OpenFOAM, was used to compute the flow field in the Reynolds number (Re) range 60-180. Results showed the presence of the periodic vortex shedding for all Re ranges and the slotted cylinders were effectively able to suppress it. The surface vorticity over the slotted cylinder surface increased by 16%-23% as compared to the normal cylinder. The momentum injection to the cylinder base reduced the strength of vortex shedding and shedding frequency for the slotted cylinders. Pressure recovery was improved due to an increase in the pressure coefficient which further led to a decrease in the pressure drag. The total drag coefficient for the slotted cylinders was lower than the normal cylinders for Re>70. Also, a comparatively lower Strouhal number was observed for the slotted cylinders.