Amplitude modulation and extreme events in turbulent channel flow

Abstract

Amplitude modulation of near-wall turbulence by large-scale structures in the outer layer is investigated by direct numerical simulation of turbulent channel flows at Reynolds number $$Re_{\tau } =540$$ , 1000, 2000. The effect of modulation is obvious in the two-point cross-section correlation map, and the correlation coefficients increase significantly with the Reynolds number. The influence of modulation is reflected in the tail of the probability density function of the near-wall flow signals, which expands as the Reynolds number increases. The flatness factor provides a quantitative description of the high fluctuation events due to modulation. Vortical structures associated with modulation are revealed by conditionally averaging the flow field of the near-wall extreme events, providing a depiction of how the influence of the large-scale structures penetrate towards the near-wall region.