The subtle effect of integral scale on the drag of a circular cylinder in turbulent cross flow

The effects of Reynolds number (Re), freestream turbulence intensity (Tu) and integral length scale (A) on the drag coefficient (Cd) of a circular cylinder in cross flow were experimentally studied for 6.45 x 103 < Re < 1.82 x 104. With the help of orificed plates, Tu was fixed at approximately 0.5%, 5%, 7% and 9% and the normalized integral length scale (L/D) was varied from 0.35 to 1.05. Our turbulent results confirmed the general trend of decreasing Cd with increasing Tu. The effectiveness of Tu in reducing Cd is found to lessen with increasing A/D. Most interestingly, freestream turbulence of low Tu (~5% ) and large A/D (~1.05 ) can increase the Cd above the corresponding smooth flow value.