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The particle image velocimetry technique was used to measure characteristics of a turbulent flow over a transitionally-rough fixed bed in an open-channel flow. These conditions are typical of flows encountered in sediment transport problems. Measurements obtained with this technique were used to investigate the distributions of velocities, turbulence intensities, Reynolds stress, and third- and fourth-order moments in a region above y + = 10. The present results are in good agreement to those previously obtained on smooth walls and provide further evidence that PIV can be applied successfully to investigate turbulence in open-channel flows over a rough bed.

[1] 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.

This paper presents an exploratory study of flow-particle interaction in a small water tunnel. Images are recorded following the Particle Image Velocimetry technique. The frames are analyzed in order to get information on flow turbulence and particles carried by the flow. The turbulence of the flow is considered in terms of the coherent structures that developed essentially in the wall region. The methods investigated allow the detection and quantitative description of these structures. Concerning the solid phase, two kinds of methods were considered: one to locate particles on the frames, and the other to track the particles. The methods are tested with simple experiments performed in a small water tunnel. Results concerning the fluid and solid phases are analyzed together. They show two kinds of particle behavior: particles that travel following coherent structures and particles that do not follow any particular turbulent structure.