Drag Reduction for Flow Past a Square Cylinder Using Rotating Control Cylinders—A Numerical Simulation

This paper investigates the effect of two control cylinders of same circular cross section on reduction of drag caused by vortex shedding phenomenon at the downstream of the flow past a square cylinder. Numerical computations are performed for a Reynolds number of 100 as this is well below the transitional flow regime where the effect of vortex shedding phenomenon is more significant. Simulations are carried out using a Finite Volume CFD solver for five different positions along with three different rotational speeds (5, 10, 20 rad/s) and directions (clockwise, anticlockwise) of control cylinders. Validation of the base case (i.e., without any control cylinder) shows a good agreement with the available literature data. The transient variations of lift and drag coefficients are monitored for each case and compared with those of the base case. The vortex shedding phenomenon and the physics behind the drag reduction are explained with the help of streamlines and drag coefficient plots. The most effective case with 4% drag reduction is identified when x_c = 0.65, y_c = 0.45 with the top cylinder rotating in the clockwise direction and the bottom cylinder rotating in the anticlockwise direction with a rotational speed of 20 rad/s.