SWIRLING FLOWS IN CIRCULAR-TO-RECTANGULAR TRANSITION DUCTS

Swirling flows in three circular-to-rectangular transition ducts, each of them with an aspect ratio of 2.0 at the rectangular exit, have bee n studied experimentally. The swirling flows were produced by swirlers whose vane angles were at 5 degrees, 10 degrees and 20 degrees inclin ded to the incoming flow, respectively. Flow visualization experiments were made at selected cross-sectional planes in the transition ducts. Pressure and velocity measurements were obtained on the contoured duc t walls and at the rectangular exit planes, respectively. The results show that the swirling flow pattern evolves into a skewed structure at the exit plane which, in connection with the wall pressure distributi ons, is asymmetric with respect to the centerline of either the top an d bottom walls or the side walls. Moreover, an analysis based on the m ean streamwise vorticity equation with the velocity data obtained imme diately downstream of the rectangular exit plane indicates that the cr oss-stream Reynolds stress plays an important role in transporting the streamwise vorticity of the swirling flow into the surrounding fluid.