Abstract
A stepped-nose with various step lengths and heights, attached to a square cylinder, can significantly reduce the drag coefficient compared to that of the square cylinder. The underlying physics are that (1) the vortices trapped in the step regions produce the thrust forces acting on the step surfaces facing against the uniform stream which cancel the drag force acting on the front surface of the stepped-nose obstacle, and (2) the tangent reattachment of the flow separating from the front surface edges to the side surfaces of the main body decreases the suction pressure acting on the back surface of the main body. In the present study, these favorable effects of the stepped-nose are experimentally documented by presenting the measurement results of surface pressure coefficient, streamwise velocity, and turbulence intensity of side flow and flow visualization pictures. It is demonstrated that when step height takes a value of about one-tenth of the main body length, there is a rather wide range of step length, for which the net drag force acting on the stepped-nose almost vanishes and the side flow is stabilized by the stepped-nose.
