A conditioned volumetric view of ``superstructure'' events in turbulent boundary layers

A conditionally averaged view of ``superstructure'' type events is presented for the case of zero pressure gradient turbulent boundary layers at friction Reynolds number, $Re_{\tau} \approx 14\,000$. Detailed boundary layer traverses are acquired above a simultaneously sampled spanwise rake of 10 flush-mounted hot-film sensors, affixed to the tunnel wall with a spanwise spacing of approximately $0.08$ boundary layer thicknesses ($\delta$). The data from the traversing probes are conditioned on the occurrence of superstructure-type footprints sensed by the wall array. The resulting data give a more complete volumetric view of the large-scale meandering log-region features than has previously been afforded by hot-wire rake and PIV measurements. Such detailed views are used to further investigate the existence of an amplitude modulation effect, in which the footprints of large $\delta$- scaled structures (that typify the logarithmic region) have been observed to modulate the viscous-scaled near-wall cycle.