Enhanced entrainment into turbulent plumes driven by suspended sediment

We present results from laboratory experiments and direct numerical simulations that examine entrainment into particle-laden turbulent plumes. Specifically, we consider a regime with dilute concentrations of small and dense particles carried by a positively buoyant plume. Within this regime, the settling velocity of the particles is smaller than and in the opposite direction to the plume velocity at all heights.

Despite the settling velocity being much smaller than the plume velocity, the presence of suspended particles is seen to enhance the entrainment of ambient fluid into the plume by approximately 30%. The increased entrainment coefficient is attributed to inertial clustering of the particles leading to regions of the plume being denser than the ambient fluid. We hypothesize that these dense regions can then be convectively unstable leading to an increased entrainment coefficient.