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Abstract The behavior of suspended particles in turbulent flows is a recalcitrant problem spanning wide‐ranging fields including geomorphology, hydrology, and dispersion of particulate matter in the atmosphere. One key mechanism underlying particle suspension is the difference between particle settling velocity (ws) in turbulence and its still water counterpart (wso). This difference is explored here for a range of particle‐to‐fluid densities (1–10) and particle diameter to Kolmogorov micro‐eddy sizes (0.1–10). Conventional models of particle fluxes that equatewstowsoresult in eddy diffusivities and turbulent Schmidt numbers contradictory to laboratory experiments. Incorporating virtual mass and Basset history forces resolves these inconsistencies, providing clarity as to whyws/wsois sub‐unity for the aforementioned conditions. The proposed formulation can be imminently used to model particle settling in turbulence, especially when sediment distribution outcomes over extended time scales far surpassing turbulence time scales are sought.
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Scalewise Return to Isotropy in Stratified Boundary Layer Flows
Abstract Anisotropic turbulence is ubiquitous in atmospheric and oceanic boundary layers due to differences in energy injection mechanisms. Unlike mechanical production that injects energy in the streamwise velocity component, buoyancy affects only the vertical velocity component. This anisotropy in energy sources, quantified by the flux Richardson numberRif, is compensated by a “return to isotropy” (RTI) tendency of turbulent flows. Describing RTI in Reynolds‐averaged models and across scales continues to be a challenge in stratified turbulent flows. Using phenomenological models for spectral energy transfers, the necessary conditions for which the widely‐used Rotta model captures RTI across variousRifand eddy sizes are discussed for the first time. This work unravels adjustments to the Rotta constant, withRifand scale, necessary to obtain consistency between RTI models and the measured properties of the atmospheric surface layer for planar‐homogeneous and stationary flows in the absence of subsidence. A range ofRifand eddy sizes where the usage of a conventional Rotta model is prohibited is also found. Those adjustments lay the groundwork for new closure schemes.
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- PAR ID:
- 10451025
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Atmospheres
- Volume:
- 125
- Issue:
- 16
- ISSN:
- 2169-897X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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