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SUMMARY:Reynolds stress fluctuation properties in the inertial sublayer of
  canonical turbulent wall-flows - Joe Klewicki (University of Melbourne)
DTSTART:20220329T083000Z
DTEND:20220329T090000Z
UID:TALK171140@talks.cam.ac.uk
DESCRIPTION:Properties of the Reynolds stress fluctuations in the inertial
  sublayer of canonical turbulent boundary layer\, channel and pipe flows a
 re explored. A broader aim here is to investigate if the self-similar prop
 erties associated with the mean momentum balance (MMB) in these flows are 
 also reflected in the statistics of the turbulent motions responsible for 
 wall-normal momentum transport. Toward this aim\, a succinct summary of an
 alytical properties admitted by the MMBs associated with these flows is us
 ed to motivate the study of the $ uv $ fluctuations\, where $u$ and $v$ ar
 e the streamwise and wall-normal velocity fluctuations\, respectively. Sta
 tistical properties of primary interest are associated with the time fract
 ion that $ uv $ time series are negative (or equivalently the negative are
 a fraction in a wall-parallel planes)\, $T_{24}$\, the skewness of $uv$\, 
 S($uv$)\, and the $uv$ correlation coefficient\, $r$ -- all of which are p
 roperties associated with the underlying $uv$ probability distribution (pd
 f). These and other properties of the Reynolds stress fluctuations are exa
 mined in the inertial sublayer of fully developed channel and pipe flows a
 nd zero pressure gradient turbulent boundary layers. The data sources incl
 ude channel flow direct numerical simulations up to friction Reynolds numb
 ers\, $\\delta^+ = 8\,000$\, laboratory pipe and boundary layer experiment
 s (up to $\\delta^+ exceeding 10\,000$)\, and field measurements in the ne
 ar-neutral atmospheric surface layer\, where $\\delta^+ = O(1 \\times 10^6
 )$. The analyses indicate that\, to within the accuracy of the measurement
 s\, both $T_{24}$ and S($uv$) approach values that correlate with the simi
 larity stretching parameter revealed in the MMB analysis\, the $uv$ pdf ex
 hibits self-similarity over the entire $\\delta^+$ range\, a Gram-Charlier
  expansion based analysis of the $uv$ pdf shows that the assumption of Gau
 ssian $u$ and $v$ statistics provides a good approximation for $T_{24}$\, 
 and that $r$ (which is a key parameter in the Gram-Charlier representation
 ) exhibits an approximately $-1/4$ power-law decay with $\\delta^+$.&nbsp\
 ;
LOCATION:Seminar Room 1\, Newton Institute
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