Tracking streaks in the buffer layer of wall-bounded turbulence

Among the many organized structures observed in near-wall turbulent flows, streaks, defined as regions of slowly moving fluid elongated in the direction of the mean flow, are considered to be of major importance for their role in the regeneration of turbulent energy. Here, we identify and track individual streaks in time using time-resolved direct numerical simulation data of a low Reynolds number channel flow. The analysis of the streaks shows that there is a clear distinction between wall-attached and detached streaks and that the former can be further categorized into streaks that are contained in the buffer layer and the ones that reach the outer region. The results reveal that streaks are born in the buffer layer, coalescing with each other to create larger streaks that are still attached to the wall. These tall-attached streaks eventually split into wall-attached and wall-detached components. The wall-detached component not only has a larger wall-normal velocity compared to its wall-attached counterpart, but it also has a larger (less negative) streamwise velocity, reminiscent of ejections or burst events.