Mon August 5th 2013
Seminar PIV and holography measurements of particle dynamics in turbulent flows
Rene van Hout


This talk will present some of the work that is done at the Environmental Multi-Phase Flow Laboratory. The first part will discuss resuspension and saltation of near neutrally buoyant, polystyrene beads in a turbulent boundary layer in a horizontal, water channel facility (Re = 7353). Lift-off coincided with the passage of a vortex core creating an ejection-sweep cycle (“burst”) responsible for lift-off. In all cases beads left the wall when immersed in near-wall ejections and exposed to positive shear. As a consequence, a high shear induced lift force coincided with bead lift-off while the Magnus force due to bead rotation and translation induced lift were negligible. The difference between resuspension and saltation was governed by the type of coherent flow structures the beads encountered when lifted out of the viscous sublayer. The second part of the talk will discuss some work on dispersal and breakup of pollen aggregates, motivated by gene exchange by wind pollinated (anemophilous) plants. PIV measurements are presented of the flow field in the wake of a mature ragweed spike with multiple staminate flowers set up in a wind tunnel and exposed to wind speeds ranging from 1 to 2 m/s. Pollen release was imaged by high-speed, inline holographic cinematography that enabled to track the pollen in a 3D volume and identify breakup events of pollen clumps. Results showed that all ragweed pollen was released in clumps containing numbers of single pollen that range from tens to several thousand. Clumps were observed to break apart in high shear rate flow regions in the vicinity of the flowers.
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The 10th Complex Motion in Fluids 2021
Max Planck Gesellschaft
Centre for Scientific Computing