What is it about?
We present several already-reported experimental examples of turbulent starting pipe flow, in which the reported mean velocity profiles show a strangely deformed shape, when compared with equal-Reynolds-number steady-state profiles. This deformation has remained unexplained for decades. We provide an analytical explanation for the experimental profiles, and we demonstrate, mathematically, that the different patterns of deformation are due to the action of the Reynolds shear stress.
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Why is it important?
To our knowledge, this research shows, for the first time, how important is the Reynolds shear stress in determining the pattern of mean velocity that a starting turbulent flow finally attains. It is a theoretical investigation, classifiable as basic research, which explores deeply into the very foundations of unsteady turbulent flows.
Perspectives
The investigation raises the role of the Reynolds shear stress as one of the main agents in configuring the mean velocity distribution in unsteady turbulent flows, to a degree comparable with the pressure gradient. We believe it will foster the interest in measuring and reporting the Reynolds shear stress in future experimental investigations of unsteady turbulent flows.
F. Javier Garcia Garcia
Universidade da Coruna
Read the Original
This page is a summary of: On the influence of Reynolds shear stress upon the velocity patterns generated in turbulent starting pipe flow, Physics of Fluids, October 2020, American Institute of Physics,
DOI: 10.1063/5.0019180.
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