Abstract
Skin-friction drag in turbulent pipe flows significantly decreases by a pulsating due to a relaminarization phenomenon. In a straight pipe flow,63% drag reduction rate has been obtained experimentally. The purpose of the present study is to investigate the drag reduction effect by the pulsating in a turbulent pipe flow with a branch. The cycleaveraged friction Reynolds number is set to be 200 before the branch. The flow rates at a main and a sub branches are set to be equal. The range of control parameters, i.e., a period of the pulsating and an acceleration parameter, that produces the drag reduction effect, is scaled with a local skin-friction velocity and a mean pressure gradient averaged for an acceleration phase. This scaling is found to be suited not only the flow before the branch, but also that after the branch. The drag reduction effect in a deceleration period mainly contributes to the drag reduction effect of pulsating.
