We use a novel experimental setup to obtain the vertical velocity and acceleration statistics of snowflakes settling in atmospheric surface-layer turbulence, for Taylor microscale Reynolds numbers ( ) between 400 and 67 000, Stokes numbers (St) between 0.12 and 3.50, and a broad range of snowflake habits. Despite the complexity of snowflake structures and the non-uniform nature of the turbulence, we find that mean snowflake acceleration distributions can be uniquely determined from the value of St. Ensemble-averaged snowflake root mean square (rms) accelerations scale nearly linearly with St. Normalized by the rms value, the acceleration distribution is nearly exponential, with a scaling factor for the (exponent) of −3/2 that is independent of and St; kurtosis scales with , albeit weakly compared to fluid tracers in turbulence; gravitational drift with sweeping is observed for St < 1. Surprisingly, the same exponential distribution describes a pseudo-acceleration calculated from fluctuations of snowflake terminal fall speed in still air. This equivalence suggests an underlying connection between how turbulence determines the trajectories of particles and the microphysics determining the evolution of their shapes and sizes.
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December 2023
Research Article|
December 19 2023
A universal scaling law for Lagrangian snowflake accelerations in atmospheric turbulence
Dhiraj K. Singh
;
Dhiraj K. Singh
(Conceptualization, Formal analysis, Investigation, Methodology, Writing – original draft, Writing – review & editing)
1
Department of Mechanical Engineering, University of Utah
, Salt Lake City, Utah 84112, USA
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Eric R. Pardyjak
;
Eric R. Pardyjak
(Conceptualization, Formal analysis, Funding acquisition, Investigation, Methodology, Project administration, Resources, Supervision, Writing – original draft, Writing – review & editing)
1
Department of Mechanical Engineering, University of Utah
, Salt Lake City, Utah 84112, USA
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Timothy J. Garrett
Timothy J. Garrett
a)
(Conceptualization, Formal analysis, Funding acquisition, Investigation, Methodology, Project administration, Supervision, Writing – original draft, Writing – review & editing)
2
Department of Atmospheric Sciences, University of Utah
, Salt Lake City, Utah 84112, USA
a)Author to whom correspondence should be addressed: tim.garrett@utah.edu
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a)Author to whom correspondence should be addressed: tim.garrett@utah.edu
Physics of Fluids 35, 123336 (2023)
Article history
Received:
August 21 2023
Accepted:
November 03 2023
Citation
Dhiraj K. Singh, Eric R. Pardyjak, Timothy J. Garrett; A universal scaling law for Lagrangian snowflake accelerations in atmospheric turbulence. Physics of Fluids 1 December 2023; 35 (12): 123336. https://doi.org/10.1063/5.0173359
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