Streak meandering without streaks

Oblique velocity fluctuations in near-wall turbulence have been regarded as a consequence of streak instabilities. However, we show that they are predominant in minimal flow units obtained from DNS simulations in which long streaks are numerically damped. What we see is that flow patterns that co-exist with streaks and had been interpreted as meandering motions remain after the streaks are removed. In fact, they are responsible for most of the turbulent production in the absence of streaks, becoming even stronger than when the latter are allowed to form. A Perron-Frobenius analysis on conditional trajectories along low-dimensional state space projections show the presence of Orr burst amplification and lift-up for the oblique modes. This points to an alternative regeneration process for these motions, which is both independent from the streaks and compatible with previous studies. Results support the idea that oblique velocity fluctuations, rather than being a by-product of streaks, can take over the role of the latter in the turbulent cycle.