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Abstract
The present work is on the stability of forced convection in a tightly coiled square duct of curvature ratio 0.5 in high Dean number region. Dynamic responses of multiple flows to finite random disturbances are examined by direct transient computation. It is found that physical realizable, fully developed flows evolve to chaotic oscillations at high values of Dean number. The power spectrum of these oscillating flows is constructed by empirical mode decomposition and Hilbert spectral analysis for the characteristics of chaotic oscillations. With increase of the Dean number, the temporal scale of chaotic oscillation becomes wider; high-frequency flows appear, and the energy contained in the bursts becomes stronger.
The authors are indebted to Dr. T. L. Yang for his discussion on numerical methods and computer codes. Financial support from the Research Grants Council of Hong Kong (RGC) and the Outstanding Young Researcher Award of the University of Hong Kong to L.W. is gratefully acknowledged.