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An analytical investigation of particle clustering in turbulence

Event Type: 
Date and Time: 
Friday, March 17, 2017 - 16:15
CTR Conference Room 103
Event Sponsor: 
Parviz Moin, Director of Center for Turbulence Research
Dr. Mahdi Esmaily-Moghadam, CTR Postdoctoral Fellow, Center for Turbulence Research, Stanford University

Clustering of inertial particles plays a key role in the formation of rain to that of the planets in our early solar system. It has been known for decades that heavy tiny particles in a turbulent flow segregate spatially, forming clusters. The degree of clustering highly depends on the particle relaxation time relative to that of the background flow, viz. the Stokes number. While minimal clustering is observed at very large or small Stokes numbers, clustering is maximized when the two time-scales are comparable and St ≈ 1. This nonmonotonic variation, although observed experimentally and reproduced numerically, is yet to be explained theoretically. At the low Stokes number regime, our theoretical knowledge is sufficient for making a quantitative prediction, whereas, for the rest of parameter space, our knowledge is qualitative at its best. Filling this gap is the objective of this study. In this talk, Dr. Mahdi Esmaily-Moghadam will paint a picture that reveals underlying mechanisms leading to cluster formation by putting together pieces obtained from a lower dimensional analysis. This pen-and-paper analysis shows the fundamental response of particles to straining and rotating flows, reveals the existence of a lower bound on the clustering rate, predicts the requirement for trajectory crossing and the asymptotic variation of the Lyapunov exponents for the full regime of Stokes and Reynolds numbers. Quantitative comparison against direct numerical simulations, including particle-laden isotropic turbulence, confirms these findings.

Dr. Mahdi Esmaily-Moghadam received his B.Sc. and M.Sc. with high distinction from Sharif University and a second M.Sc. and Ph.D. in Mechanical Engineering from UCSD in 2014. During his doctoral studies, he developed several numerical techniques for multiscale simulation of the circulatory system and proposed a novel surgical design for single ventricle heart patients. Currently, as a postdoctoral scholar at the Center for Turbulence Research at Stanford University, he is studying the interaction of inertial particles with turbulent flows in the context of solar receivers. His research interests center around the study of emerging applications in cardiovascular mechanics and particle-laden flows and development of multiscale computational techniques for such applications.