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Title: Navier-Stokes Equations Do Not Describe the Smallest Scales of Turbulence in Gases

Abstract

In turbulent flows, kinetic energy is transferred from the largest scales to progressively smaller scales, until it is ultimately converted into heat. The Navier-Stokes equations are almost universally used to study this process. Here, by comparing with molecular-gas-dynamics simulations, we show that the Navier-Stokes equations do not describe turbulent gas flows in the dissipation range because they neglect thermal fluctuations. We investigate decaying turbulence produced by the Taylor-Green vortex and find that in the dissipation range the molecular-gas-dynamics spectra grow quadratically with wave number due to thermal fluctuations, in agreement with previous predictions, while the Navier-Stokes spectra decay exponentially. Furthermore, the transition to quadratic growth occurs at a length scale much larger than the gas molecular mean free path, namely in a regime that the Navier-Stokes equations are widely believed to describe. In fact, our results suggest that the Navier-Stokes equations are not guaranteed to describe the smallest scales of gas turbulence for any positive Knudsen number.

Authors:
; ORCiD logo; ORCiD logo; ORCiD logo
Publication Date:
Research Org.:
Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA)
OSTI Identifier:
1854611
Alternate Identifier(s):
OSTI ID: 1888554
Report Number(s):
SAND2022-3088J
Journal ID: ISSN 0031-9007; PRLTAO; 114501
Grant/Contract Number:  
NA0003525
Resource Type:
Published Article
Journal Name:
Physical Review Letters
Additional Journal Information:
Journal Name: Physical Review Letters Journal Volume: 128 Journal Issue: 11; Journal ID: ISSN 0031-9007
Publisher:
American Physical Society
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; kinetic theory; turbulence

Citation Formats

McMullen, Ryan M., Krygier, Michael C., Torczynski, John R., and Gallis, Michael A. Navier-Stokes Equations Do Not Describe the Smallest Scales of Turbulence in Gases. United States: N. p., 2022. Web. doi:10.1103/PhysRevLett.128.114501.
McMullen, Ryan M., Krygier, Michael C., Torczynski, John R., & Gallis, Michael A. Navier-Stokes Equations Do Not Describe the Smallest Scales of Turbulence in Gases. United States. https://doi.org/10.1103/PhysRevLett.128.114501
McMullen, Ryan M., Krygier, Michael C., Torczynski, John R., and Gallis, Michael A. Mon . "Navier-Stokes Equations Do Not Describe the Smallest Scales of Turbulence in Gases". United States. https://doi.org/10.1103/PhysRevLett.128.114501.
@article{osti_1854611,
title = {Navier-Stokes Equations Do Not Describe the Smallest Scales of Turbulence in Gases},
author = {McMullen, Ryan M. and Krygier, Michael C. and Torczynski, John R. and Gallis, Michael A.},
abstractNote = {In turbulent flows, kinetic energy is transferred from the largest scales to progressively smaller scales, until it is ultimately converted into heat. The Navier-Stokes equations are almost universally used to study this process. Here, by comparing with molecular-gas-dynamics simulations, we show that the Navier-Stokes equations do not describe turbulent gas flows in the dissipation range because they neglect thermal fluctuations. We investigate decaying turbulence produced by the Taylor-Green vortex and find that in the dissipation range the molecular-gas-dynamics spectra grow quadratically with wave number due to thermal fluctuations, in agreement with previous predictions, while the Navier-Stokes spectra decay exponentially. Furthermore, the transition to quadratic growth occurs at a length scale much larger than the gas molecular mean free path, namely in a regime that the Navier-Stokes equations are widely believed to describe. In fact, our results suggest that the Navier-Stokes equations are not guaranteed to describe the smallest scales of gas turbulence for any positive Knudsen number.},
doi = {10.1103/PhysRevLett.128.114501},
journal = {Physical Review Letters},
number = 11,
volume = 128,
place = {United States},
year = {Mon Mar 14 00:00:00 EDT 2022},
month = {Mon Mar 14 00:00:00 EDT 2022}
}

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