Abstract
Subcritical transition to turbulence in wall-bounded shear flow is known to be characterized in terms of turbulent patches bounded by laminar regions. In circular pipe flow, it is observed that turbulence is localized only in the streamwise direction at marginal Reynolds numbers. Such a structure is a so-called turbulent puff. A turbulent puff is known to decay according to a memoryless process, so that its lifetime has an exponential probability distribution. In rectangular-duct flow, when the aspect ratio is small, i.e., As < 4, a turbulent puff is observed; however, it would exhibit difference from a usual puff as in a pipe. In this study, the decay of a turbulent puff in rectangular-duct flow is measured experimentally by using LDV(Laser Doppler Velocimeter) and PIV(Particle Image Velocimetry). It is found that the survival probability of a turbulent puff is exponential as in pipe flow, but its lifetime is very different from that at the comparable Reynolds number in pipe flow.
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