Insights into the Effect of Confinement on Swirling Flow by PIV

Confinement with a rectangular cross-section is commonly used to simulate the role of a swirl combustor, yet its effect on swirling flows remains poorly understood. This study investigates the influence of confinement on the isothermal flow field of a counter-rotating swirler. A particle image velocimetry (PIV) system was employed to measure the swirling flow field under varying confinement ratios at an air pressure drop equivalent to 3% of atmospheric pressure. The results reveal two distinct flow patterns, delineated by a critical confinement ratio of approximately 8.92. Detailed analyses of the velocity components, contour distributions, and Reynolds shear stresses were conducted. The two flow patterns are attributed to the wall attachment effect and swirling intensity, respectively. Furthermore, the results confirm that the swirling flow field is primarily governed by the confinement ratio.