Non-linear temporal dynamics of large-scale structures and turbulence dissipation in turbulent channel flow*

The non-linear dynamics emanating from large-scale structures are explored in channel flow based on DNS datasets up to Reτ≈2000 using minimal computational box for large-scale structures (following Hwang & Cossu, Phys. Rev. Lett., 2010). Volume-averaged temporal correlations between TKE and turbulence dissipation show a well-defined average time lag similar to observations in homogeneous isotropic turbulence by Goto & Vassilicos (Phys. Lett. A, 2015). In channel flow, the TKE produced at large scales is strongly correlated with the large-scale streaks which break down with a downstream meandering motion. The correlation analysis suggests that the TKE in the intermediate layer is transported towards both the core and near-wall regions and dissipated there with a time-lag that is combined with a wall-distance lag. In the path towards the core region the wall-distance lag is equal to the time lag multiplied by the skin friction velocity, particularly if we condition on ejection events, and represents a non-linear interspace/interscale transfer process. The time lag found in the volume averaged picture ensues from both this time-space lag to the core but also from the time-space lag to the wall. The dissipation through the near-wall region has a wider spread of space-time lags and involves a non-trivial energisation of turbulence production in the near-wall and log regions.