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Results from a flow visualization study of Dean vortex flow are presented. These were obtained over a range of Dean numbers from 40 to 220 using a transparent channel with mild curvature, an aspect ratio of 40 to 1, and an inner to outer radius ratio of 0.979. Observations and photographs show evidence of pairs of counter-rotating Dean vortices indicated by mushroom-shaped smoke patterns for Dean numbers greater than 64 and angular positions at least 85° from the start of curvature. Photographs showing nonsymmetric Dean vortices with rocking motion are presented and believed to be evidence of a twisting mode of oscillations. Dean vortices with oscillations mostly in the radial direction are also observed, which are believed to strongly depend on the small amplitude disturbances that trigger initial vortex development. Photographic evidence of small secondary vortex pairs, and vortices with simultaneous radial and spanwise oscillations are also given along with a domain map showing the experimental conditions for different types of vortex behavior.
Ligrani et al. (Thu,) studied this question.