The Study about Drag Reduction of a Circular Cylinder with Grooves

In this study, two kinds of circular cylinders which cut grooves to the cylinder surface for the purpose of cylinder drag reduction were produced. One of which is the circular cylinder which set 2 grooves in the cylinder upstream side, and other is the circular cylinder which provided 6 grooves every 60 degrees. Experiments were performed using a wind tunnel varying an attack angel α = 0 to 60 degrees in the range of Reynolds number Re= 1×104 to 1.2×105. The relationship between a Strouhal number and Reynolds number, the pressure distribution on the surface of cylinder, the flow feature around the cylinder, and drag reduction effect were investigated. As the results of experiments, in the case of 2 groove cylinder, 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 degrees, in the range of Re > 4×104. However, it became clear that the drag reduction effect was lost as an attack angle α is attached. In order to compensate this weak point, the 6 groove cylinder was proposed, and the characteristic test was performed. It was obtained that the cylinder with the deep depth of groove is not influenced by the direction of wind. The value of drag coefficient was about 56% of value of the drag coefficient of smooth cylinder. It was shown that the wake width of the proposed cylinders narrows from the wake width of the smooth cylinder.