Abstract

There is a growing body of evidence that the nature of wall-bounded turbulence can be associated to a continuum of nonlinear self-sustained dynamical processes whose kinematic counterparts in the logarithmic layer are Townsend’s attached eddies. Linear energy amplification mechanisms play an important role in these dynamical processes and in the selection of the most energetic turbulent structures. I will argue that the definition of the linear operator, and in particular the inclusion (or not) of the effect of Reynolds stresses in it, has profound consequences on linear analyses of the amplifications of mean flow perturbations. It will be shown that second-order correlations can be well predicted by suitably modeling Reynolds stresses in resolvent analyses of constant-density turbulent channel flows where no information is available on forcing statistics. It will be also shown that the same type of modeling is necessary to predict the onset of turbulent large-scale convection in unstably stratified turbulent channels.