A Numerical Study on the Drag of Axial Cylinder

In this study, the numerical analysis for the flows around an axial cylinder is carried out in order to investigate the basic characteristics of drag of blunt body. A variation of drag and flow separation for the axial cylinder is investigated according to the length-diameter ratio. Also, the flow separation around the head is removed by rounding-off the front edge of the body to analyze the effect of drag reduction. Most of the drag turns out to be a pressure drag component and the variation of drag is caused by the change of pressure and velocity which is affected strongly by the flow separation at the edges of the axial cylinder. Especially, it is found that the pressure drag component acting on the back of axial cylinder, as known as the base drag, mainly changes the drag. As the length-diameter ratio of axial cylinder increases, the drag sharply decreases and the minimum is shown when the length-diameter ratio is about 2.4. Also, as the length-diameter ratio increases further above 2.4, the drag increases at a slower rate. The pressure drag is almost constant when the length-diameter ratio is greater than 8, but the increase of friction drag component is the reason for the increase of the drag. When flow separation is removed completely at the front edge of the axial cylinder, the pressure drag component is reduced to 12~17%, but the total drag is reduced to only 17%~32% due to the friction drag component that increases linearly proportional to the length-diameter ratio.