POD-based study of turbulent plane Poiseuille flow: comparing structure and dynamics between quasi-linear simulations and DNS

Turbulence in the restricted nonlinear (RNL) dynamics is analysed and compared with direct numerical simulations (DNS) of Poiseuille turbulence at Reynolds number $R=1650$ . The structures are obtained by proper orthogonal decomposition (POD) analysis two components flow partition used RNL dynamics: streamwise mean fluctuations. POD indicates that dominant modes, both DNS dynamics, roll-streaks harmonic spanwise direction. However, we conclude these modes do not occur isolation but rather Fourier a coherent roll-streak structure. fluctuations reveals similar complex consisting part oblique waves collocated streak. origin identified their correspondence to predicted using stochastic model (STM). These dominated optimally growing on streak, which STM predicts correctly be sinuous wave This close between structure associated DNS, implies self-sustaining mechanism operating essentially same as has been previously optimal perturbation growth