抄録
Measurements were made of mean and fluctuating velocity profiles in the wake flow of the five kinds of stepped circular cylinders varying the diameter from a big one to a small cylinder at the midpoint of the span. Furthermore, we measured vortex shedding frequencies and compared them to that of a straight cylinder. Hot-wire survey shows that mean velocity profiles were largely distorted in S-shape depending on the diameter rations of cylinders in the center line of the cylinder, moreover, having the flat-type and W-type in shape at the big cylinder underneath the step. In addition, turbulent intensity were at same regions where mean velocity profiles having the flat-type shape. This indicates that the secondary flow induced by the longitudinal vortices disturbed the velocity field of wake flow. As a result, vortex shedding frequencies decreased linearly with the diameter ratios and velocity fluctuation induced these vortices were decreased at the big cylinder.
