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Joseph Nettesheim

Department of Atmospheric and Oceanic Sciences, UW-Madison

A Numerical Study on the Aerodynamics of Freely Falling Planar Ice Crystals

Room 811 AOSS, June 14, 2017, 2:30 PM

Abstract

Fluid flow fields and fall patterns of falling planar ice crystals are studied by numerically solving the unsteady, incompressible Navier-Stokes equations using a commercially available computational fluid dynamics package. The ice crystal movement and orientation are explicitly simulated based on hydrodynamic forces and torques representing the six degrees of freedom (three in translation, three in rotation). This study extends the current framework by investigating four planar-type ice crystals: crystals with sector-like branches, crystals with broad branches, stellar crystals, and ordinary dendritic crystals. The ice crystals range from 0.1 to 0.5 and 1 to 5 mm in maximum dimension, corresponding to Reynolds number ranges 0.2 to 384. The results indicate that steady flow fields are generated for Reynolds flow less than 100; larger plates generate unsteady flow fields and exhibit horizontal translation, rotation, and oscillation. Empirical formulas for drag coefficient, terminal velocity, and ventilation effect are given. Fall trajectory, pressure distribution, wake structure, vapor field, and vorticity field are examined.



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