A minimal flow unit of the logarithmic layer in the absence of near-wall eddies and large scales

In the vicinity of walls, turbulent flows are found to be highly organized, consisting of streamwise rolls and low- and high-speed streaks (Klebanoff et al. 1962; Kline et al. 1967; Smith & Metzler 1983; Blackwelder & Eckelmann 1979; Johansson et al. 1987) that are involved in a quasi-periodic regeneration cycle (Robinson 1991; Panton 2001; Adrian 2007; Smits et al. 2011; Jiménez 2018). Important progress regarding the study of this regeneration cycle was made using the "minimal flow unit" approach, which indicated that buffer layer streaks can self-sustain even when motions at larger scales are inhibited and that their existence, therefore, relies on an autonomous process (Jiménez & Moin 1991). The observation that the buffer and viscous layers of wall-bounded flows can be simulated in periodic boxes of minimal dimensions has been useful in understanding wall turbulence since it enables the study of individual flow features in isolation from their mutual interactions.