Flow Characteristics of Pulsatile Turbulent Flow in a 90° Pipe Bend

Abstract

The characteristics of pulsatile turbulent flow in a 90° pipe bend with a radius ratio of Rc=4 were investigated experimentally. Experiments were conducted with a mean Reynolds number Reta=20000, Womersley numbers of α=10 and 30, and flow ratio of η=0.5. The axial and secondary flow velocities were measured by laser Doppler velocimetry in sections from upstream to downstream of the bend. The periodic changes in their distributions were investigated and the effects of α on their transitions along the bend axis were discussed. For a low α, the flow velocities exhibited periodical changes similar to a steady flow with instantaneous Re. However, with an increase in α, they changed abruptly near the bend exit and became more complex. In particular, the axial velocity distribution at the maximum flow rate exhibited a peculiar change in the latter half of the bend, changing to a depressed shape with two maxima from a triangle, and the secondary flow velocity intensified significantly near the bend exit. Simultaneously, the turbulence intensity increased, and just behind the bend exit, the region with a large value extended to the central region.