Analysis of intermittent turbulence in stably stratified channel flow*

Under sufficiently strong stratification, fully developed turbulent channel flows could transition to intermittent flows where laminar and turbulent patches coexist. Intermittency complicates the conventional statistics approach when describing turbulence. Using direct numerical simulations, we analyze the turbulence quantities under the effect of intermittency. The numerical simulations cover a range of friction Reynolds and Richardson numbers, which enables us to investigate the boundary at which transitions from fully turbulent to intermittent occur in the parameter space for stably stratified channel flow. The volume fraction of turbulent patches in each simulation is quantified, based on which we attempt to predict the occurrence of intermittency in the parameter space. Our results suggest that the intermittency criterion documented for stratified plane Couette flow (Deusebio et al., J. Fluid Mech., volume 781, 2015) does not apply to channel flows. Alternative criteria for the intermittency boundary are sought.