Near-wall cycle amplitude modulation in turbulent boundary layers

A non-linear influence of the large-scale log-region motions onto the small-scale near-wall cycle is found to exist in the buffer and log-region of turbulent boundary layers. Based on recent observations of Hutchins & Marusic (2007b) in high Reynolds number turbulent boundary layers, a novel procedure is developed to evaluate the modulation effect. This is done using tools based on Hilbert transformations applied to the spectrally filtered small-scale component of fluctuating velocity signals. The procedure allows us to quantify the modulation level of small-scale motions imparted by the superstructure type-events. Further analysis shows a high degree of robustness for this method.