Transient, Oscillatory and Steady Characteristics of Dean Vortex Pairs in a Curved Rectangular Channel
When Dean numbers are high enough, the flow in a curved channel is unstable to centrifugal instabilities, and secondary flows develop which eventually form into pairs of counter-rotating vortices. This flow is referred to as Dean vortex flow, and the accompanying pairs of streamwiseoriented vortices are referred to as Dean vortices. The present paper describes some transient, oscillatory, and steady characteristics of Dean vortex pairs in a curved rectangular channel with 40 to 1 aspect ratio and an inner to outer radius ratio of 0.979. In particular, attention is focussed on secondary instabilities observed in the form of oscillatory motions called twisting and undulating, and in the form of transient events consisting of splitting and merging of vortex pairs. Splitting and merging events are described from visualizations of flow in spanwise/radial planes at Dean numbers of 75 and 100 in the form of two distinctly different types of splitting events, and four distinctly different types of merging events. Even though these transient events produce fairly large amplitudes of unsteadiness, the Dean vortex pairs have preferred positions across the span of the channel about which the motion occurs. These preferred positions are evident from time-averaged distributions of streamwise velocity, which show a variety of steady vortex pair characteristics.
KeywordsSecondary Flow Streamwise Velocity Vortex Pair Concave Surface Splitting Event
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- Ligrani, P. M., Longest, J. E., Kendall, M. R., Fields, W. A., and Fuqua, S. J., 1992b, Splitting, merging and spanwise wavenumber selection of Dean vortex pairs during their initial development in a curved rectangular channel, Physics of Fluids A ,submitted.Google Scholar