Drag reduction technique of cylinder and mechanism research

The hydrogen bubble flow visualization technique has been used to study the flow around a hollow circular cylinder with several splits and the drag reduction mechanism. The experiments cover the cylinder with different number and arrangement of splits, different angle of attack. The primary criterion of drag reduces is whether the splits change wake of the hollow cylinder. According to this criterion, the experimental result indicates when the attack of a split is in the range of |α|≤60°, the cylinder possesses drag reduction characteristics, and the optimum angle of attack is 20°. Under this condition, a two-dimensional jet flow is visible in the downstream split, which affects the wake flow pattern. However, when the attack of the split is equal to 70°≤|α|≤90°, the split can hardly affect the drag of the cylinder.