Experimental investigation of ejections and sweeps involved in particle suspension

Abstract

Experiments involving particle-laden flows were conducted to study interactions between ejections and suspended particles. Three types of beads and four hydraulic conditions are tested (10,000 < Re < 30,000). A two-dimensional Particle Image Velocimetry technique was applied to measure turbulent characteristics and particle motion simultaneously. The study also focused on the type and intensity of turbulent structures involved in bead suspension. Applying quadrant analysis to the flow in the vicinity of each moving bead, observations showed that upward particle movement is strongly correlated to the presence of ejections in the vicinity of the particle. For a given experiment, all particles surrounded by ejections with an instantaneous value of momentum flux greater than a critical value move upward with a positive vertical velocity. Once made dimensionless by the particle buoyant weight per unit area, the critical momentum flux is weakly dependent on the flow Reynolds number Re. From the statistical analysis a conceptual model of particle motion within an ejection is proposed. Copyright 2009 by the American Geophysical Union.