Relationship between Turbulence Modulation and Skewness in Wall Bounded Flows

Recent investigations into wall-bounded turbulent flows have shown a nonlinear scale interaction, whereby the largescale motion amplitude modulates the small-scale structures (Hutchins & Marusic, 2007b). Mathis et al. (2009) developed a scheme to quantify the degree of modulation using a decoupling procedure, based on the Hilbert transformation applied to the filtered small-scale component of the fluctuating streamwise velocity; and highlighted the similarity between the wall-normal evolution of the degree of amplitude modulation and the skewness profile. This became the topic of study by Schlatter & Örlü (2010), who questioned this technique (at least at low Reynolds number) for unambiguously detecting and quantifying the effect of large-scale amplitude modulation of the small scales. The present study provides a complementary analysis of the relationship between the degree of amplitude modulation and the skewness using experimental and synthetic signals. It is shown that the Reynolds number trend in the skewness profile is related to the amplitude modulation of the small-scales by the large-scale signal.