Wake flow modification behind a square cylinder using control rods

In the present study, flow behind a square cylinder is investigated using control rods. The control rods are placed in the shear layer and studied using particle image velocimetry, hotwire anemometry and flow visualization techniques. Experiments are conducted in a low-speed wind tunnel for three different Reynolds numbers 485, 805 and 1290. However, detailed analysis of flow is only presented at a Reynolds number of 485. The aim is to modify the wake behind a square cylinder for possible suppression of vortex Street and drag reduction. The control rod diameter is kept constant as 0.2 times of the cylinder diameter. Depending upon the gap between control rods and the cylinder, the flow structure, vortex dynamics, the distance of the shear layer roll up behind the cylinder is modified. An attempt is made to correlate the different flow structures with corresponding drag forces. Several parameters such as time-averaged drag coefficient, Strouhal number, recirculation length, fluctuating velocity, turbulence intensity, and Reynolds stress are measured. To understand the flow phenomena and its intricate structure, flow visualization images are also captured in the same setup with smoke visualization. Maximum up to 22% drag reduction is observed at a particular control rod position.