Cloud droplets nucleate on dust particles when warm, moist air rises and cools to supersaturation vapor conditions in the upper atmosphere. The droplets initially grow by condensation until they reach a few tens of microns when coalescence takes over as the dominant mechanism for growth. Classical models in the meteorological literature assume the coalescence is predominantly driven by the differential settling of droplets of different sizes. However, the time required to reach this end stage mechanism can be much shorter than these microphysical models predict. It is believed that atmospheric turbulence could explain the acceleration of cloud formation. Turbulence impacts the droplet processes in multiple ways: (i) due to the density mismatch, droplets tend to cluster outside of vortices, increasing their collision rate; (ii) droplet relative motions are enhanced by turbulence; and (iii) turbulence increases the coalescence efficiency of droplet collisions. We will review evidence for all three mechanisms based on direct numerical simulations and experiments of droplet laden turbulence performed by us and our collaborators.
Lance Collins, Cornell University
Room number or other detail:
Friday, May 3, 2019 - 12:30pm
Lance R. Collins is serving his second term as the Joseph Silbert Dean of Engineering at Cornell University. Prior to that he was the S. C. Thomas Sze Director of the Sibley School of Mechanical & Aerospace Engineering. In 2011, he was part of the team that successfully bid to partner with New York City to build Cornell Tech, which opened its Roosevelt Island campus in 2017. In his role as dean, Collins has accelerated the college’s efforts in diversity. Since 2007, Cornell Engineering tripled the proportion of underrepresented minority students from 7 to 21 percent, and increased the percentage of undergraduate women from 28 to 50 percent, more than twice the national average. For these efforts, he received the inaugural Mosaic Medal of Distinction from Cornell Mosaic and the Edward Bouchet Legacy Award from the Bouchet Graduate Honor Society.
Collins is a professor of mechanical and aerospace engineering. His research is focused on the application of direct numerical simulation to a broad range of turbulent processes. He has been elected fellow of the American Physical Society, the American Association for the Advancement of Science, and the American Institute of Chemical Engineers. In 2014, he received the William Grimes Award from the AIChE. Collins graduated from Princeton in 1981 with high honors and holds a Ph.D. from the University of Pennsylvania, all in chemical engineering.