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Multi-Structure Turbulence in a Boundary Layer with a Uniformly Sheared Free StreamLivingston, Curtis 02 September 2020 (has links)
A turbulent boundary layer (TBL), generated in a water tunnel, extended to a highly
turbulent and anisotropic “free stream” that consisted of a uniformly sheared flow
(USF) with a mean shear that was in the opposite direction to that in the TBL. Extensive measurements of the fluctuating velocity were taken with the use of hot-film
anemometry, laser Doppler velocimetry and particle image velocimetry. On either
side of the TBL edge, defined as the location of maximum velocity, the turbulence
relaxed to its canonical structures in TBL and USF, respectively, but, in the vicinity
of the edge, the turbulence was multi-structure and exhibited strong departures from
canonical behaviour. Of particular interest was the variation of the dissipation parameter, which, in contrast to its near-constancy in well-developed canonical flows,
varied inversely proportionally to the turbulence Reynolds number. The entire flow
contained horseshoe-shaped coherent structures, whose properties, however, varied
from the TBL, across the multi-structure region and into the USF.
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