68th Annual Meeting of the APS Division of Fluid Dynamics (November 22, 2015 — November 24, 2015)

P0014: Pollen, Water, and Wind - Chaotic mixing in a puddle of water

  • Kaare H. Jensen, Department of Physics, Technical University of Denmark, Kgs. Lyngby, Denmark
DOI: https://doi.org/10.1103/APS.DFD.2015.GFM.P0014

Pollen from pine trees was remarkably abundant in 2012, when a largely dry spring brought more than usual. The photograph shows how pollen grains have mixed in a shallow puddle of water (width ~1 m, depth ~1 cm). The flows revealed by nature’s tracer particles may influence nutrient distribution in puddles and small ponds.

Water puddles are ubiquitous and provide habitat for a vast array of living organisms. For instance, as breeding grounds for mosquitoes of the genus Anopheles that transmits malaria, a disease responsible for the death of 584.000 people in 2013. The larvae feed on e.g. algae and bacteria in the surface layer. 

Wind blowing across a puddle causes a shear stress at the interface, which drives a flow in the liquid below. Chaotic mixing can occur if the wind direction changes over time. A fluid patch is repeatedly stretched and folded into itself, resulting in a drastic reduction of the length over which molecules have to diffuse. 

Location: Cambridge, Massachusetts, USA.

WHO Malaria Fact sheet N°94 (2015)

C. Kranenburg, J. Hydraulic Research, 30(1), 29-46 (1992)

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