Flow Visualization in a Circular-to-Rectangular Transition Duct

This work reports on flow behaviors near the wall and secondary flow structures in a circular-to-rectangular transition duct at Reynolds numbers of 104. Flow visualization experiments were conducted under the conditions of uniform and swirling inlet flows. As found, flow structures observed at the rectangular exit under the swirling inlet condition appear very differently from those observed under the uniform inlet condition. In the former case the secondary flows are developed due to the detachments of the swirling flow from the contoured wall, while in the latter case the secondary flows are known due to the mechanism of meanflow straining in the corner regions.