Cut Through Thick Branches with the Wood Ranger Power Shears

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Transient development mechanisms operating on streaky shear flows are believed vital for sustaining close to-wall turbulence. Of the three particular person mechanisms current - Orr, raise-up and ‘push-over’ - Lozano-Duran et al. J. Fluid Mech. 914, A8, 2021) have lately observed that each Orr and push-over should be present to sustain turbulent fluctuations given streaky (streamwise-independent) base fields whereas lift-up does not. We present here, using Kelvin’s model of unbounded constant shear augmented by spanwise streaks, that it is because the push-over mechanism can act in concert with a ‘spanwise’ Orr mechanism to produce a lot-enhanced transient progress. Rey) instances. Our results therefore help the view that while carry-up is believed central for the roll-to-streak regenerative course of, it is Orr and push-over mechanisms that are both key for the streak-to-roll regenerative course of in close to-wall turbulence. Efforts to understand wall-bounded turbulence have naturally focussed on the wall and the (coherent) buildings which kind there (Richardson, 1922). The consensus is that there's (at the least) a close to-wall sustaining cycle (Hamilton et al., 1995; Waleffe, 1997; Jimenez & Pinelli, 1999) involving predominantly streaks and streamwise rolls (or vortices) which helps maintain the turbulence (e.g. see the opinions Robinson, 1991; Panton, 2001; Smits et al., 2011; Jimenez, 2012, 2018). The era of these streaks from the rolls is usually defined by the (linear) transient progress ‘lift-up’ mechanism (Ellingsen & Palm, 1975; Landahl, 1980), but how rolls are regenerated from the streaks has proven a little less clear attributable to the need to invoke nonlinearity at some point.

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