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Exploring the connection between interfacial bulging at the edge of the turbulent boundary layer and large-scale motions near the wall

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We here explore the apparent connection between the large-scale interfacial bulging that is known to occur at the intermittent turbulent / non-turbulent interface of the turbulent boundary layer, and the very large-scale motions (or superstructures) that have been recently shown to predominate the logarithmic region of the layer. Building upon recent observations of amplitude modulation between large and small-scale structures in the turbulent boundary layer, we probe further the apparent link between superstructure events in the logarithmic region and zones of increased small scale turbulent activity at the edge of the boundary layer. Through analysis of the hotwire signals close to the outerlimit of the boundary layer, we demonstrate that increased small-scale activity at the edge of the layer is strongly associated with bulging. By conditioning these hotwire signals with simultaneously acquired fluctuating wall shear stress signals, we demonstrate that the interfacial bulging is associated with a very large-scale footprint at the wall (consistent with the scaleand arrangements that have previously been reported for very large scale motions). For the final conference presentation, this analysis will be extended to include recent large field-of-view high resolution PIV data obtained at Re_tau~=14000 in the high Reynolds number
boundary layer wind tunnel at the University of Melbourne.

Author(s):

Nicholas Hutchins    
University of Melbourne
Australia

Jason Monty    
University of Melbourne
Australia