Two regimes of dilute turbulent settling suspensions under shear

When turbulent flow is laden with negatively buoyant particles, their mean distribution over the direction of gravity can induce stable density gradients that penalize turbulent fluctuations. This effect is studied numerically for shear-driven flow with dilute non-inertial sediment. The turbulent dynamics and sediment transport depend critically on particle settling velocity $v_s$, splitting into two regimes: homogeneous weakly stratified turbulence and flow with developed turbulence atop an intermittent boundary layer. At intermediate $v_s$, neither state can be sustained and the flow laminarizes.