Abstract
The fluid flow and drag reduction of a circular cylinder with small grooves were investigated. The positions of upstream and downstream sides of the grooves on the cylinder, θf and θr, were 50 - 70 degrees, 55 - 74 degrees and 60 - 78 degrees from the stagnation point of the cylinder. Experiments were performed for the above three models and smooth cylinder varying the attack angle α = 0 to 45 degrees in the range of Reynolds number, Re = 104-105. The Strouhal number of the cylinder with grooves increases from 0.20 to 0.28-0.30, the base pressure coefficient rises from -1.4 to -0.8, then the drag coefficient decreases from 1.3 to 0.55 at α + θf < 80 degree, in the range of Re > 4×104. The surface oil-flow patterns show that the shear layers separated from the front of the groove reattach on the rear groove of the cylinder. This effect is due to the turbulent transition and turbulent separation. The wake width decreases and the location of the vortex formation region goes downstream.
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