Effect of a Small Control Rod on the Aerodynamic Forces and Wake Structure of Side-by-Side Cylinders at moderate Reynolds Number

The unsteady wake interaction between two side-by-side circular cylinders often leads to significant vortex shedding and fluctuating aerodynamic forces. This numerical study investigates the effect of a small passive control rod with a rod-to-cylinder diameter ratio d/D = 0.07 on the wake dynamics and aerodynamic forces of two side-by-side circular cylinders. Two configurations are explored: one where the control rod is placed directly behind the cylinders (x/D = 0), and another where it is located downstream (x/D = 0.5). The two cylinders are arranged with a center-to-center spacing ratio T/D = 1.25. The simulations were performed at Reynolds number of 1.2X104 using the Reynolds-Averaged Navier–Stokes (RANS) equations with the (SST) k-w turbulence model in ANSYS Fluent. In the uncontrolled case, the flow exhibits unsteady flip-flopping behavior and asymmetric vortex shedding, typical of closely spaced cylinder interactions. When the control rod was positioned directly behind the two cylinders (x/D = 0), the wake instability and flip-flopping behavior were completely suppressed. This configuration led to the formation of two stable recirculation zones in the wake behind each cylinder. Consequently, the mean drag coefficient decreased by 9.4%, while the root mean square of the lift coefficient increased by 97%, relative to the uncontrolled case. Conversely, placing the control rod further downstream at (x/D = 0.5) also contributed to flow stabilization but produced larger recirculation zones. This resulted in a 9.3% increase in the mean drag coefficient and a 61% increase in the lift coefficient. These results demonstrate that the rod placed directly behind the cylinders (x/D = 0) provides more favourable aerodynamic performance and better flow stabilization