Lift-up, Kelvin–Helmholtz and Orr mechanisms in turbulent jets

Dynamics of shear-layer coherent structures in a forced wall-bounded flow

“…Recently, these wavepackets have also been found to be one of the main sources of sound generation in turbulent jets (Cavalieri et al 2012(Cavalieri et al , 2013 especially at shallow angles, as also suggested by earlier works (Mollö-Christensen & Narasimha 1960;Mollo-Christensen 1967;Crighton 1975;Michalke & Fuchs 1975). Recent detailed characterisations of wavepackets in turbulent jets are provided by Sasaki et al (2017), Schmidt et al (2018), Pickering et al (2020), taking advantage of data from a well-validated large-eddy simulation (Brès et al 2018).…”

“…2019; Pickering et al. 2020), two coherent structures related to each other by the lift-up effect, are also present in the analysis. Nonlinear interactions leading to vortex regeneration, which is known to be one of the important processes in the self-sustained process in turbulence of wall-bounded flows (Hamilton et al.…”

“…(2018), Pickering et al. (2020), taking advantage of data from a well-validated large-eddy simulation (Brès et al. 2018).…”

The effect of streaks on the instability of jets

“…A linear analysis of the mean flow confirmed that the transient growth of these structures is caused by the lift-up effect. Pickering et al (2020) investigated the formation of streaks in developing jets, obtained from large-eddy simulation, in response to harmonic forcing input, concluding that streaks may be expected to dominate perturbations in jets at low frequencies.…”

Nonlinear input/output analysis: application to boundary layer transition

“…Trefethen et al (1993) and Jovanović & Bamieh (2005) showed that the computation of the optimal forcings and responses of the resolvent operator extracts the pseudo-resonances of a flow field, that is, the frequencies and spatial distributions of forcings that optimally trigger linear responses in a system. In a set-up where the streamwise direction is also discretised (in addition to the cross-stream direction), accurate methods to extract the optimal features from the global resolvent have first been carried out with time-stepper approaches by Blackburn, Barkley & Sherwin (2008), Åkervik et al (2008), Monokrousos et al (2010) and more recently with sparse direct LU methods by Sipp et al (2010), Brandt et al (2011), Rigas et al (2017), Schmidt et al (2018), Pickering et al (2020), among others.…”