Modal and nonmodal stability analysis of turbulent stratified channel flows

This work aims at studying the modal and nonmodal stability of stably stratified turbulent channel flow, assessing the influence of stratification at fixed friction Reynolds number. When increasing the stratification, the energy gain for streamwise-independent perturbations increases by two orders of magnitude, and the spanwise wavenumber for which the energy gain peaks reaches values comparable to those reported in the direct numerical simulations. Moreover, for nonzero values of the streamwise and spanwise wavenumbers, {α} and {β}, the energy gain curve has two peaks, one for shorter target times and {α}>{β}, leading to a center-channel temperature peak, and another for {α}larger target times.