Abstract
Experimental investigation for a periodically converging-diverging turbulent pipe flow is performed to examine a spatial development of a drag reduction effect. A shape of the pipe is designed according to a result of a direct numerical simulation. Three periods of the converging-diverging are provided. At the bulk Reynolds numbers in the range of 3000 to 5000, the maximum drag reduction rates are 29% at the first period, 39% at the second period, and 46% at the third period respectively. Therefore, the drag reduction rate is found to develop in the downstream direction. On the other hand, the drag reduction effect is deteriorate over the bulk Reynolds number of 5000.
