Journal
INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS
Volume 61, Issue 6, Pages 658-682Publisher
WILEY
DOI: 10.1002/fld.1979
Keywords
oscillating square cylinder; lock-in; vortex shedding; vortex switch; energy transfer; vorticity
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This paper reports simulation results for free-stream flow past an oscillating square cylinder at Re= 100 and 150, for oscillating-to-natural-shedding frequency ratios of 0.5 <= f(r)<= 3.0 at a fixed oscillation amplitude of 0.2 of the cylinder width. The transformed governing equations are solved in a non-inertial frame of reference using the finite volume technique. The 'lock-in' phenomena, where the vortex shedding becomes one with the oscillation frequency, is observed near the natural shedding frequency (f(r)approximate to 1). Beyond the synchronization band, downstream recovery of the wake to its stationary (natural) state (frequency) is observed in cross-stream velocity spectra. At higher forcing frequencies, a phase lag between the immediate and the far wake results in a shear layer having multi-polar vortices. A 'Vortex-switch' accompanied by a change in the direction of energy transfer is identified at the 'lock-in' boundaries. The variation of aerodynamic forces is noticed to be different in the lock-in regime. The velocity phase portrait in the far wake revealed a chaotic state of flow at higher excitation though a single (natural) frequency appears in the spectra. Copyright (C) 2008 John Wiley & Sons, Ltd.
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