Document Type

Article

Author ORCID Identifier

Tim Berk https://orcid.org/0000-0002-7159-2360

Filippo Coletti https://orcid.org/0000-0001-5344-2476

Journal/Book Title/Conference

Journal of Fluid Mechanics

Volume

975

Publisher

Cambridge University Press

Publication Date

11-22-2023

Creative Commons License

Creative Commons Attribution 4.0 License
This work is licensed under a Creative Commons Attribution 4.0 License.

First Page

1

Last Page

23

Abstract

Inertial particles in wall-bounded turbulence are known to form streaks, but experimental evidence and predictive understanding of this phenomenon is lacking, especially in regimes relevant to atmospheric flows. We carry out wind tunnel measurements to investigate this process, characterizing the transport of microscopic particles suspended in turbulent boundary layers. The friction Reynolds number Re𝜏 = O(104) allows for significant scale separation and the emergence of large-scale motions, while the range of viscous Stokes number St+ = 18–870 is relevant to the transport of dust and fine sand in the atmospheric surface layer. We perform simultaneous imaging of both carrier and dispersed phases along wall-parallel planes in the logarithmic layer, demonstrating that streamwise particle streaks largely overlap with large-scale low-speed flow regions. The fluid–particle slip velocity indicates that with increasing inertia, the particle streaks outlive the low-speed fluid streaks. Moreover, two-point statistics show that the width of the particle streaks increases linearly with Stokes number, bounded by the size of the coherent flow structures. Finally, the particle-sampled flow topology suggests that particle streaks reside between the legs of hairpin packets. From these observations, we infer a conceptual view of the formation of particle streaks in the frame of the attached eddy model. A scaling for the particle streaks’ width is derived as a function of Re𝜏 and St+, which reproduces the measured trends and predicts widths O(0.1) m in the atmospheric surface layer, comparable to aeolian streamers observed in the field.

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