Abstract
The reduction of drag of a circular disk of length/diameter ratio c/d=0.3 to 0.55 in axial flow was investigated. The drag coefficient of a circular disk with blunt shape of c/d=0.05 is about. 1.17 in the range Re=104 to 106. In the cases of c/d = 0.5 and 1.0, the drag coefficients are 1.13 and 0.91, respectively. To control the flow field around the circular disk, the side wall is cut to a spherical surface. Namely, the circular disk consists of two circular plane surfaces and a spherecal surface. The front and rear corners of the spherical surface located at 53°and 90°-120°from the front stagnation angle on a sphere, respectively. The surface oil-flow patterns indicated that the shear layer separated from the front corner reattaches on a spherical surface of the disk, and then the transition in the boundary layer and the turbulent separation occur. As the results, the wake width visualized by a smoke decreases drastically and the base pressure coefficient rises. The drag coefficient obtained by integrating the pressure distribution around the three circular disks with a spherical surface decreases by about a quarter of those of the three standard circular disks.
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