The effect of flowrate and bluff body on a confined swirling flow using Stereo-PIV

The study investigates the influence of the Reynolds number and a disc-shaped bluff body positioned along the axial direction on the average velocity of a confined swirling flow in a circular pipe. The velocity measurements show that increasing the Reynolds number from 67,000 to 103,000 raises the peak value of three mean velocity components, with the axial velocity increasing by up to 65%, tangential velocity by 60%, and radial velocity by 50%. Moreover, the two-dimensional mean radial velocity distribution in the axial plane reveals a distinctive “cat's-eye” pattern caused by the wavy radial velocity distribution near the center of the pipe. The presence of a disc-shaped bluff body alters the size, sign, and magnitude of the cat's-eye patterns, increasing the peak radial velocity by approximately 22%. Q-criterion analysis on the flow field is performed to identify coherent vortical structures and explain the impact of circular disc obstacles on the flow.