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SUMMARY:The outer zone of turbulent boundary layers  - Prof. Javier Jimén
 ez
DTSTART:20160506T120000Z
DTEND:20160506T130000Z
UID:TALK64843@talks.cam.ac.uk
CONTACT:Antoine Debugne
DESCRIPTION:sing data from new simulations of the turbulent boundary layer
 \, we describe several features of the outer zone of wall-bounded flow at 
 relatively high  Reynolds numbers (Reth=6600). For example\, using two-poi
 nt velocity correlations\, we show that the size and inclination of the di
 fferent velocity components are different\, and interpret this as represen
 ting different moments in their evolution. Other features are not so well 
 understood. E.g.\, the transverse components (v and w) are similar in boun
 dary layers and channels\, but the streamwise velocity is much longer in t
 he latter\, and the outer zone of boundary layers is characterized by a la
 rge-scale oblique organization of w\, of unknown origin\, but reminiscent 
 of some of the transitional structures observed in extended Couette flow.\
 n\nWe next discuss the turbulent/nonturbulent interface\, detailing with s
 ome care the effect of how the interface is defined\, including the variab
 le being thresholded\, the thresholding details\, and the thresholding lev
 el. We note that the definition of distance between a point and a surface 
 has a profound effect on the definition of the interface and\, particularl
 y\, on the conditional analysis of the flow in its neighbourhood. We intro
 duce an appropriate distance and show that the interface undergoes a topol
 ogical transition as the threshold is increased and the interface enters t
 he turbulent core. This can be used to define a 'natural' threshold\, and 
 we show that this definition clarifies\, at least for this flow\, some of 
 the hypotheses that have been advanced about the interface structure. A si
 mple structure is proposed which roughly agrees with some of the older pro
 posals by Townsend and others.  
LOCATION:LR3B\, Inglis Building\, CUED.
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