Pulsatile Turbulent Flow in a 90.DEG. Bend.

Abstract

Distributions of velocity and turbulence intensity in pulsatile flow through a circular-sectioned 90-degree bend when an undeveloped flow with a rectangular axial velocity distribution was introduced were examined experimentally. Measurements were made using a hot-wire probe at the axial Reynolds number based on time-mean velocity of 3×104 and the frequency parameter α(=a√(ω/ν), a : internal radius of pipe, ω : angular frequency, ν : kinematic viscosity of fluid) of 28.0 and 72.3 for a bend whose radius of the centerline curvature is 5.0 times the pipe radius. At α=28.0, axial velocities and turbulence intensities vary in time proportionally to the instantaneous volumetric flow rate. On the other hand, at α=72.3, the axial velocity profile shows a configuration differing from that of quasi-steady flow at each phase angle near the inner wall. With cyclic changes of the velocity profile, the turbulence intensities near the inner wall are also subject to a large change during one cycle, that is, they decrease during the accelerating period and increase in the decelerating one. However, they were found to exhibit only a slight change near the outer wall.