The 3D flow patterns of the generation and growth of the unstable streamwise vortices during the transition phase of fluid flow in a 2D curved channel were visualized by use of. the hydrogen bubble technique and a laser light sheet. The spatial development of the disturbances during the transition were recorded by means of video tapes and photographes. Based on the linear and weakly nonlinear analyses, the features of transitional flow in the curved channel such as the non-existance of the subcritical instability and the selection of wavenumber were discussed.
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