抄録
Direct numerial simulations for periodically diverging-converging turbulent pipe flows are perfromed to examine a drag reduction effect. The friction Reynolds number is set to be 110 and five different pipe shapes are examined. The maximum drag reduction rate of 14% is obtained when the ratio between the pipe length and the maximum deformation thickness is 797. The turbulent puff is observed in the pipe flow by the visualization of vortical structures.
