From: Transition in Wall-Bounded Flows Date of download: 10/12/2017 Copyright © ASME. All rights reserved. From: Transition in Wall-Bounded Flows Appl. Mech. Rev. 2008;61(3):030802-030802-21. doi:10.1115/1.2909605 Figure Legend: Left column: a few typical hydrogen-bubble photos of complex flow structures illuminated by laser sheet at different horizontal heights. The SCS (SCS↑), the secondary closed vortex (SV↑), Λ-vortex (Λ↑), and the first ring vortex (FRV↑) are shown. Right column: a three-dimensional structure reconstructed from the photos on the left column, with the corresponding laser sheets locations marked and high-density hydrogen-bubble traces sketched thereon.