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The Significance of Hairpin Vortices in Turbulent Boundary Layers

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The elementary question whether hairpin vortices constitute an inherent, universal structure of wall turbulence at moderate and high Reynolds numbers (Re) is addressed in this study. The downstream evolution of a single, artificial hairpin vortex is first studied in a mean shear flow to investigate possible decay and package-creation processes under high Re conditions. In a second step, hairpin-dominated flow in a transitional turbulent boundary layer is considered, whereas the lifetime of individual vortices and possible connection mechanisms are evaluated. The statistics obtained from this flow regime will be compared with reference data from turbulent-boundary-layer studies employing different transition mechanisms. Vortex eduction will be applied to comprehend the evolution from a well organized to a more chaotic state. The results could explain discrepancies in boundary-layer data close to transition and will contribute to the discussion about the relevance of hairpin-like structures in fully developed wall turbulence.

Author(s):

Georg Eitel-Amor    
Linne FLOW Centre, KTH Mechanics
Sweden

Ramis Orlu    
Linne FLOW Centre, KTH Mechanics
Sweden

Philipp Schlatter    
Linne FLOW Centre, KTH Mechanics
Sweden