Thu September 29th 2011
16:00
HR Z109
Journal Club Single-drop fragmentation determines size distribution of raindrops
Pascal Sleutel

Details:

Although France does not enjoy as much as rain as many other countries in the world we like to study it anyway because it is such an ordinary and calming event. Next to a very nice movie we will use lots of scaling laws, weber number analysis and fancy integrals to elucidate our results. Like many natural objects, raindrops are distributed in size. By extension of what is known to occur inside the clouds, where small droplets grow by accretion of vapor and coalescence, raindrops in the falling rain at the ground level are believed to result from a complex mutual interaction with their neighbours. We show that the raindrops’ polydispersity, generically represented according to Marshall–Palmer’s law (1948), is quantitatively understood from the fragmentation products of non-interacting, isolated drops. Both the shape of the drops’ size distribution, and its parameters are related from first principles to the dynamics of a single drop deforming as it falls in air, ultimately breaking into a dispersion of smaller fragments containing the whole spectrum of sizes observed in rain. The topological change from a big drop into smaller stable fragments—the raindrops—is accomplished within a timescale much shorter than the typical collision time between the drops.




Nature Physics 20 july 2009. Emmanuel Villermaux and Benjamin Bossa
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