Suppression of vortex shedding in flow around a square cylinder using control cylinder

The closeness or matching of the self-sustained vortex shedding excitation with the structural frequency of the body may cause resonance resulting in structural failures. The present study aims at the suppression of vortex shedding using a passive method, by placing a small control cylinder in the near wake of the main cylinder. Square control cylinders of sides either 20%, 25% or 30% of the main cylinder are employed to change the dynamics of the flow. Direct numerical simulation (DNS) of two-dimensional, unsteady, incompressible flow past a square cylinder at Reynolds numbers of 75, 100 and 125 has been carried out. The Navier-Stokes equations are solved using Marker and Cell (MAC) method with the second-order spatial and temporal discretizations. Computed results indicate that there exists an explicit spatial domain present on the edges of the separating shear layers in the near wake within which the placement of the control cylinder guarantees complete suppression. The mechanism of the suppression may be attributed to an effective increase in vorticity diffusion of the separating shear layer. Also, changes in the control cylinder size and Reynolds number have a considerable effect on the vortex shedding suppression. A remarkable drag reduction of the main cylinder is also achieved for partial as well as complete suppression. The study also highlights that the partial suppression of vortex shedding results in significant reductions in Strouhal number, and fluctuating lift and drag forces. The control behavior of the flow past a square cylinder surprisingly resembles that of the flow past a circular cylinder. (C) 2019 Elsevier Masson SAS. All rights reserved.