Some characteristics of the coherent structures in turbulent boundary layers
The present work describes the results of an experimental study about the kinematics of the coherent structures in an open channel flow. The coherent events, detected in the near-wall region, are analysed by an original method based on conditional-sampling. Using simple kinematic characteristics occurring during the bursting events the coherent structures are grouped into several clusters obtaining a substantial improvement over the classical conditional average. In this way different kinds of coherent structures are distinguished, and probably ascribed to different phases of the same group of coherent structures. In particular, we show experimental evidence supporting the hypothesis about coherent packets of hairpin vortices formulated by Zhou et al. 1999 even at high Reynolds number. This analysis of the near-wall region is realised by means of a new experimental technique which allows an accurate measurement of the streamwise and wall-normal turbulent velocity components (u and v respectively) in the flow field very close to the wall.
KeywordsReynolds Stress Turbulent Boundary Layer Coherent Structure Secondary Peak Open Channel Flow
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