Documentation of the role of large-scale structures in the bursting process in turbulent boundary layers

Abstract

The scaling of the bursting frequency with Reynolds number is investigated experimentally by means of hot-wire measurements in turbulent boundary layers over the range 1580 < Reθ < 23 700. Bursting events are detected by means of the u-level technique, and the effect of filtering and the choice of the threshold are also assessed. We find that the inner scaling produces excellent collapse of the high-pass filtered data in the buffer and log regions, regardless of the cutoff frequency and the threshold. This is due to the fact that the high-pass filter attenuates the low frequency component of the streamwise velocity signal, which is associated with large-scale structures in the flow. On the other hand, the bursting frequency scales with outer variables when the time-series is low-pass filtered with very low cutoff frequencies, highlighting the connection between bursting phenomena and the outer flow.