Drag reduction of a circular cylinder in an air-stream

To control the flow around a circular cylinder in air-stream, a rod was set upstream of the circular cylinder. The diameter of cylinder, D, was 40 mm, and the diameter of rod, d, ranged from 1 to 10 mm. The distance between the axes of the circular cylinder and rod, L, was 50–120 mm. The Reynolds number based on D ranged from 1.5×104 to 6.2×104. Two flow patterns with and without vortex shedding from the rod occurred. The flow pattern changes depending on the rod diameter, its position and the Reynolds number. The optimum conditions of the drag reduction are d/D=0.25, L/D=1.75–2.0, in these conditions, vortices do not shed from the rod and the shear layer from the rod reattaches on the front face of the circular cylinder. The reduction of the total drag including the drag of the rod is 63% compared with that of a single cylinder.