Event Date/Time
Location
Bowen Hall Rm 222
Series/Event Type
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.
Speaker Bio
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.