Acoustic precipitation enhancement technology uses strong low-frequency sound waves to enhance the relative motion and thus the collisional growth of cloud droplets, leading to increased rainfall. As a forward-looking technology, acoustic precipitation enhancement is viewed to be low-cost, environmentally friendly, simple to operate, and easy to promote. However, the science behind this technology, namely, turbulent cloud microphysics and dynamics under the action of sound waves, is a challenging multi-scale, multi-physics, and interdisciplinary research topic.  In this talk, I will first review previous theoretical understanding on the mechanisms of acoustic agglomeration and related collision kernels, and discuss how the magnitude of these collision kernels compared to collision kernels due to gravitational settling motion and turbulent air fluctuations. We then solve the stochastic collection equation under the combined actions of gravity and acoustic waves, to study how acoustic waves affect the collisional growth of cloud droplets. In particular, we study how the growth rate depends on the frequency, the applied duration, and intensity of sound waves. It is found that an optimal wave frequency exists and its value depends on the initial droplet size distribution, applied duration, and wave intensity. We also compare our findings with previous experimental observations and theoretical results. 

Dr. Lian-Ping Wang received a Batchelor’s degree in Mechanics from Zhejiang University, Hangzhou, China in 1984, and a PhD in Mechanical Engineering from Washington State University in 1990. He was then a Visiting Research Associate at Brown University from 1990 to 1992, after which he was a Research Associate at Pennsylvania State University from 1992 to 1994 and an Assistant Professor of Mechanical Engineering at the University of Delaware from 1994 to 2001. He became an Associate Professor in 2001 and a Professor in 2010 at the University of Delaware. In 2017, he was appointed a Chaired Professor at Southern University of Science and Technology, China.

Dr. Wang’s areas of expertise include computational fluid dynamics, turbulence, particle-laden flow and immiscible multiphase flow, and their applications to industrial and atmospheric processes. In recent years, he has focused on the mesoscopic CFD method based on Boltzmann equation and its application in direct numerical simulation of complex flows. He has published close to 200 refereed journal papers and has given over 100 invited talks.  Dr. Wang became an elected Fellow of American Physical Society in 2011 and an elected Fellow of American Society of Mechanical Engineers in 2016.  He became an Associate Editor of Journal of Fluid Mechanics in May 2022.