Bulk Richardson number 1 Channel flow 1 Constant flow 1 Direct-numerical-simulation 1 Eddy Diffusivities 1 Eddy viscosity 1 Flow structure 1 Impulse response 1 Large-scale flow structure 1 Linear modeling 1 Linear operators 1 Linearization 1 Mathematical operators 1 Navier Stokes 1 Navier Stokes equations Turbulent channel flows 1 Viscous flow 1