Intermittent structures of intense inter-scale energy fluxes in turbulent channel flow

The phenomenology of turbulence energy cascade is believed to be well characterized by Kolmogorov’s theory of energy cascade. However, the theory becomes increasingly inaccurate at small scales because of small-scale intermittency. Recent studies have supported a causal influence of energy cascade on small-scale intermittency (Vela-Martín, A., 2022. J. Fluid Mech., 937, p.A13.). In this work, we characterize the spatial intermittency of inter-scale energy flux at various scales, down to the dissipative (Kolmogorov) scales, in a turbulent channel flow. A band-pass filter-based multiscale analysis is used for this purpose. We characterize the skewness and kurtosis of the energy flux distribution as a function of wall-normal distance and Reynolds number. Preliminary results show that kurtosis of inter-scale energy flux increases as we move towards smaller scales and also as we go away from the wall. As kurtosis is a measure of the ‘tailedness’ of distribution, this observation suggests an increased presence of intense intermittent events. We use a simple threshold to isolate structures of intense inter-scale energy flux and subsequently characterize their morphology using Minkowski functionals. We also try to establish a correlation between the intermittent structures identified across all scales.