Flow control behind a circular cylinder by control rods in uniform stream

Flow control by rods of various sizes attached to the rearward stagnation point of a circular cylinder is investigated in a circulating water channel using a 2-frame gray level cross-correlation Particle Image Velocimetry (PIV) technique. Experiments are performed at Reynolds numbers between Re=5000 and Re=20,000, based on free stream velocity and the main circular cylinder diameter (D=50 mm). Time-mean velocity fields, turbulence intensity, and Reynolds shear stress are measured with four control rods and four step Reynolds numbers. The wake formation behind a cylinder was influenced by the interaction between the upper and lower sides of the wake, due to the effect of the control rods. Each control rod had distinctive characteristics. However, there was no one optimum control rod for all Reynolds numbers. The control rod d/D=0.3 had an outstanding effect on reducing the turbulence intensity, with vortex formation strongly suppressed by the control rod in its near wake. Strong turbulence intensity appeared within X/D=2.5 for all cases. (C) 2011 Elsevier Ltd. All rights reserved.