78 巻 (2012) 787 号 p. 521-530
A pulsating turbulent pipe flow has been experimentally examined for the energy saving. The rotating speed of a centrifugal pump was periodically changed for generating the pulsating flow. The cycle-averaged friction Reynolds number is set to be 110 for comparison with the previous data of direct numerical simulation (DNS) by Sasou et al.(16). In the acceleration period, the drag reduction rate increases with decreasing the amplitude of the mean pressure gradient in the acceleration phase with the longer acceleration period. As for the deceleration period, the drag reduction rate increases with larger negative mean pressure gradient in the deceleration period with the shorter deceleration period. The maximum cycle-averaged energy saving and drag reduction rates are respectively 58% and 63% when the cycle period normalized by the friction velocity and the radius is 10 and the mean pressure gradients in the acceleration and deceleration phases are respectively 4.1 and -0.93 times as large as the cycle-averaged pressure gradient.